2017-05-08 20:47:34 -07:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								# Template Syntax
  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-30 00:03:22 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								# 模板语法
  
						 
					
						
							
								
									
										
										
										
											2017-03-30 20:04:18 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								< style >  
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								  h4 {font-size: 17px !important; text-transform: none !important;}
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  .syntax { font-family: Consolas, 'Lucida Sans', Courier, sans-serif; color: black; font-size: 85%; }
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  h4 .syntax { font-size: 100%; }
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								< / style >  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-26 15:11:02 +03:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								The Angular application manages what the user sees and can do, achieving this through the interaction of a
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								component class instance (the *component* ) and its user-facing template.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								Angular 应用管理着用户之所见和所为,并通过 Component 类的实例(*组件*)和面向用户的模板来与用户交互。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-26 15:11:02 +03:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								You may be familiar with the component/template duality from your experience with model-view-controller (MVC) or model-view-viewmodel (MVVM).
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								In Angular, the component plays the part of the controller/viewmodel, and the template represents the view.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								从使用模型-视图-控制器 (MVC) 或模型-视图-视图模型 (MVVM) 的经验中,很多开发人员都熟悉了组件和模板这两个概念。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  在 Angular 中,组件扮演着控制器或视图模型的角色,模板则扮演视图的角色。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  
							 
						 
					
						
							
								
									
										
										
										
											2017-07-10 10:01:54 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								This page is a comprehensive technical reference to the Angular template language.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								It explains basic principles of the template language and describes most of the syntax that you'll encounter elsewhere in the documentation.
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-08-04 08:47:51 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								这是一篇关于 Angular 模板语言的技术大全。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								它解释了模板语言的基本原理,并描述了我们将在文档中其它地方遇到的大部分语法。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-06-09 16:05:16 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								Many code snippets illustrate the points and concepts, all of them available
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								in the < live-example  title = "Template Syntax Live Code" > < / live-example > .
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-08-04 08:47:51 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								这里还有很多代码片段用来解释技术点和概念,它们全都在< live-example  title = "模板语法的在线例子" > < / live-example > 中。
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								{@a  html}
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								## HTML in templates
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								## 模板中的HTML
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								HTML is the language of the Angular template.
							 
						 
					
						
							
								
									
										
										
										
											2017-04-26 15:11:02 +03:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								Almost all HTML syntax is valid template syntax.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The `<script>`  element is a notable exception;
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								it is forbidden, eliminating the risk of script injection attacks.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								In practice, `<script>`  is ignored and a warning appears in the browser console.
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 15:36:40 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								See the [Security ](guide/security ) page for details.
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								HTML 是 Angular 模板的语言。几乎所有的HTML语法都是有效的模板语法。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								但值得注意的例外是`<script>` 元素,它被禁用了,以阻止脚本注入攻击的风险。(实际上,`<script>` 只是被忽略了。)
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								参见[安全 ](guide/security )页了解详情。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-26 15:11:02 +03:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								Some legal HTML doesn't make much sense in a template.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The `<html>` , `<body>` , and `<base>`  elements have no useful role.
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Pretty much everything else is fair game.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								有些合法的 HTML 被用在模板中是没有意义的。`<html>` 、`<body>` 和`<base>` 元素这个舞台上中并没有扮演有用的角色。剩下的所有元素基本上就都一样用了。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-26 15:11:02 +03:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								You can extend the HTML vocabulary of your templates with components and directives that appear as new elements and attributes.
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								In the following sections, you'll learn how to get and set DOM (Document Object Model) values dynamically through data binding.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
										 
							
							
								可以通过组件和指令来扩展模板中的 HTML 词汇。它们看上去就是新元素和属性。接下来将学习如何通过数据绑定来动态获取/设置 DOM( ) 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Begin with the first form of data binding— interpolation— to see how much richer template HTML can be.
							 
						 
					
						
							
								
									
										
										
										
											2017-07-30 12:32:56 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								我们首先看看数据绑定的第一种形式 —— 插值表达式,它展示了模板的 HTML 可以有多丰富。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-10 16:51:13 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< hr / >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								{@a  interpolation}
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								## Interpolation ( <span class="syntax">{{...}}</span> )
  
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								## 插值表达式 ( <span class="syntax">{{...}}</span> )
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								You met the double-curly braces of interpolation, `{{`  and `}}` , early in your Angular education.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								在以前的 Angular 教程中,我们遇到过由双花括号括起来的插值表达式,`{{` 和`}}` 。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.html"  region = "first-interpolation"  title = "src/app/app.component.html"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								You use interpolation to weave calculated strings into the text between HTML element tags and within attribute assignments.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								插值表达式可以把计算后的字符串插入到 HTML 元素标签内的文本或对标签的属性进行赋值。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.html"  region = "title+image"  title = "src/app/app.component.html"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								The text between the braces is often the name of a component property. Angular replaces that name with the
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								string value of the corresponding component property. In the example above, Angular evaluates the `title`  and `heroImageUrl`  properties
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								and "fills in the blanks", first displaying a bold application title and then a heroic image.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
										 
							
							
								在括号之间的“素材”, 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
										 
							
							
								  上例中, `title` 和`heroImageUrl` 属性的值,并把它们填在空白处。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  首先显示粗体的应用标题,然后显示英雄的图片。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								More generally, the text between the braces is a **template expression**  that Angular first **evaluates** 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								and then **converts to a string** . The following interpolation illustrates the point by adding the two numbers:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
										 
							
							
								一般来说,括号间的素材是一个**模板表达式**, 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  下列插值表达式通过把括号中的两个数字相加说明了这一点:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.html"  region = "sum-1"  title = "src/app/app.component.html"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								The expression can invoke methods of the host component such as `getVal()` , seen here:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
										 
							
							
								这个表达式可以调用宿主组件的方法,就像下面用的`getVal()` : 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.html"  region = "sum-2"  title = "src/app/app.component.html"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								Angular evaluates all expressions in double curly braces,
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								converts the expression results to strings, and links them with neighboring literal strings. Finally,
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								it assigns this composite interpolated result to an **element or directive property** .
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								Angular 对所有双花括号中的表达式求值,把求值的结果转换成字符串,并把它们跟相邻的字符串字面量连接起来。最后,把这个组合出来的插值结果赋给**元素或指令的属性**。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								You appear to be inserting the result between element tags and assigning it to attributes.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								It's convenient to think so, and you rarely suffer for this mistake.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Though this is not exactly true. Interpolation is a special syntax that Angular converts into a
							 
						 
					
						
							
								
									
										
										
										
											2017-04-30 22:10:32 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								[property binding ](guide/template-syntax#property-binding ), as is explained [below ](guide/template-syntax#property-binding-or-interpolation ).
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								表面上看,我们在元素标签之间插入了结果和对标签的属性进行了赋值。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								这样思考起来很方便,并且这个误解很少给我们带来麻烦。
							 
						 
					
						
							
								
									
										
										
										
											2017-07-30 12:32:56 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
										 
							
							
								但严格来讲, , 属性绑定 ](guide/template-syntax#property-binding ), 后面 ](guide/template-syntax#property-binding-or-interpolation )将会解释这一点。
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								But first, let's take a closer look at template expressions and statements.
							 
						 
					
						
							
								
									
										
										
										
											2017-07-30 17:40:53 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								讲解属性绑定之前,先深入了解一下模板表达式和模板语句。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-10 16:51:13 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< hr / >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								{@a  template-expressions}
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								## Template expressions
  
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								## 模板表达式
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								A template **expression**  produces a value.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Angular executes the expression and assigns it to a property of a binding target;
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								the target might be an HTML element, a component, or a directive.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								模板**表达式**产生一个值。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  Angular 执行这个表达式,并把它赋值给绑定目标的属性,这个绑定目标可能是 HTML 元素、组件或指令。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The interpolation braces in `{{1 + 1}}`  surround the template expression `1 + 1` .
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 15:36:40 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								In the [property binding ](guide/template-syntax#property-binding ) section below,
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								a template expression appears in quotes to the right of the  `=`  symbol as in `[property]="expression"` .
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								`{{1 + 1}}` 中所包含的模板表达式是`1 + 1` 。 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  在[属性绑定 ](guide/template-syntax#property-binding )中会再次看到模板表达式,它出现在`=` 右侧的引号中,就像这样:`[property]="expression"` 。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-31 12:23:16 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								You write these template expressions in a language that looks like JavaScript.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Many JavaScript expressions are legal template expressions, but not all.
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								编写模板表达式所用的语言看起来很像 JavaScript。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  很多 JavaScript 表达式也是合法的模板表达式,但不是全部。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-31 12:23:16 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								JavaScript expressions that have or promote side effects are prohibited,
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								including:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								JavaScript 中那些具有或可能引发副作用的表达式是被禁止的,包括:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								*  assignments (`=` , `+=` , `-=` , ...) 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  赋值 (`=` , `+=` , `-=` , ...)
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  
							 
						 
					
						
							
								
									
										
										
										
											2017-03-31 12:23:16 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								*  < code > new</ code >  
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  `new` 运算符
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  
							 
						 
					
						
							
								
									
										
										
										
											2017-03-31 12:23:16 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								*  chaining expressions with < code > ;</ code >  or < code > ,</ code >  
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  使用`;` 或`,` 的链式表达式
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								*  increment and decrement operators (`++`  and `--` ) 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								  自增或自减操作符 (`++` 和`--` )
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-31 12:23:16 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								Other notable differences from JavaScript syntax include:
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								和 JavaScript语 法的其它显著不同包括:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								*  no support for the bitwise operators `|`  and `&`  
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  不支持位运算`|` 和`&` 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  
							 
						 
					
						
							
								
									
										
										
										
											2017-05-22 13:00:38 -07:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								*  new [template expression operators ](guide/template-syntax#expression-operators ), such as `|` , `?.`  and `!` . 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-30 00:03:22 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								  具有新的[模板表达式运算符 ](guide/template-syntax#expression-operators ),比如`|` 、`?.` 和`!` 。
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								{@a  expression-context}
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								### Expression context
  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								### 表达式上下文
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The *expression context*  is typically the _component_  instance.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								In the following snippets, the `title`   within double-curly braces and the
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								`isUnchanged`  in quotes refer to properties of the `AppComponent` . 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								典型的*表达式上下文*就是这个**组件实例**,它是各种绑定值的来源。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								在下面的代码片段中,双花括号中的`title` 和引号中的`isUnchanged` 所引用的都是`AppComponent` 中的属性。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.html"  region = "context-component-expression"  title = "src/app/app.component.html"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								An expression may also refer to properties of the _template's_  context
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 15:36:40 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								such as a [template input variable ](guide/template-syntax#template-input-variable ) (`let hero` )
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								or a [template reference variable ](guide/template-syntax#ref-vars ) (`#heroInput` ).
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								表达式的上下文可以包括组件之外的对象。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  比如[模板输入变量 ](guide/template-syntax#template-input-variable ) (`let hero` )和[模板引用变量 ](guide/template-syntax#ref-vars )(`#heroInput` )就是备选的上下文对象之一。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.html"  region = "context-var"  title = "src/app/app.component.html"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								The context for terms in an expression is a blend of the _template variables_ ,
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								the directive's _context_  object (if it has one), and the component's _members_ .
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								If you reference a name that belongs to more than one of these namespaces,
							 
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								the template variable name takes precedence, followed by a name in the directive's _context_ ,
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								and, lastly, the component's member names.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								表达式中的上下文变量是由*模板变量*、指令的*上下文变量*(如果有)和组件的*成员*叠加而成的。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								如果我们要引用的变量名存在于一个以上的命名空间中,那么,模板变量是最优先的,其次是指令的上下文变量,最后是组件的成员。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								The previous example presents such a name collision. The component has a `hero` 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								property and the `*ngFor`  defines a `hero`  template variable.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The `hero`  in `{{hero.name}}` 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								refers to the template input variable, not the component's property.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								上一个例子中就体现了这种命名冲突。组件具有一个名叫`hero` 的属性,而`*ngFor` 声明了一个也叫`hero` 的模板变量。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								在`{{hero.name}}` 表达式中的`hero` 实际引用的是模板变量,而不是组件的属性。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								Template expressions cannot refer to anything in
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								the global namespace. They can't refer to `window`  or `document` . They
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								can't call `console.log`  or `Math.max` . They are restricted to referencing
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								members of the expression context.
							 
						 
					
						
							
								
									
										
										
										
											2017-07-30 17:40:53 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								模板表达式不能引用全局命名空间中的任何东西,比如`window` 或`document` 。它们也不能调用`console.log` 或`Math.max` 。
							 
						 
					
						
							
								
									
										
										
										
											2017-07-30 17:40:53 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								它们只能引用表达式上下文中的成员。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								{@a  no-side-effects}
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								{@a  expression-guidelines}
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								### Expression guidelines
  
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								### 表达式指南
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Template expressions can make or break an application.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Please follow these guidelines:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								模板表达式能成就或毁掉一个应用。请遵循下列指南:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 15:36:40 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								*  [No visible side effects ](guide/template-syntax#no-visible-side-effects ) 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  [没有可见的副作用 ](guide/template-syntax#no-visible-side-effects )
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 15:36:40 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								*  [Quick execution ](guide/template-syntax#quick-execution ) 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  [执行迅速 ](guide/template-syntax#quick-execution )
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 15:36:40 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								*  [Simplicity ](guide/template-syntax#simplicity ) 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  [非常简单 ](guide/template-syntax#simplicity )
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 15:36:40 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								*  [Idempotence ](guide/template-syntax#idempotence ) 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								  [幂等性 ](guide/template-syntax#idempotence )
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The only exceptions to these guidelines should be in specific circumstances that you thoroughly understand.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								超出上面指南外的情况应该只出现在那些你确信自己已经彻底理解的特定场景中。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								#### No visible side effects
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								#### 没有可见的副作用
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								A template expression should not change any application state other than the value of the
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								target property.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								模板表达式除了目标属性的值以外,不应该改变应用的任何状态。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								This rule is essential to Angular's "unidirectional data flow" policy.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								You should never worry that reading a component value might change some other displayed value.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The view should be stable throughout a single rendering pass.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								这条规则是 Angular “单向数据流”策略的基础。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								永远不用担心读取组件值可能改变另外的显示值。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								在一次单独的渲染过程中,视图应该总是稳定的。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								#### Quick execution
  
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								#### 执行迅速  
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Angular executes template expressions  after every change detection cycle.
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								Change detection cycles are triggered by many asynchronous activities such as
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								promise resolutions, http results, timer events, keypresses and mouse moves.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Expressions should finish quickly or the user experience may drag, especially on slower devices.
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								Consider caching values when their computation is expensive.
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								Angular 执行模板表达式比我们想象的频繁。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								它们可能在每一次按键或鼠标移动后被调用。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								表达式应该快速结束,否则用户就会感到拖沓,特别是在较慢的设备上。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								当计算代价较高时,应该考虑缓存那些从其它值计算得出的值。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								#### Simplicity
  
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								#### 非常简单  
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Although it's possible to write quite complex template expressions, you should avoid them.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								虽然也可以写出相当复杂的模板表达式,但不要那么写。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								A property name or method call should be the norm.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								An occasional Boolean negation (`!` ) is OK.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Otherwise, confine application and business logic to the component itself,
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								where it will be easier to develop and test.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								常规是属性名或方法调用。偶尔的逻辑取反 (`!` ) 也还凑合。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								其它情况下,应在组件中实现应用和业务逻辑,使开发和测试变得更容易。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								#### Idempotence
  
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								#### 幂等性
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								An [idempotent ](https://en.wikipedia.org/wiki/Idempotence ) expression is ideal because
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								it is free of side effects and improves Angular's change detection performance.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								最好使用[幂等的 ](https://en.wikipedia.org/wiki/Idempotence )表达式,因为它没有副作用,并且能提升 Angular 变更检测的性能。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								In Angular terms, an idempotent expression always returns *exactly the same thing*  until
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								one of its dependent values changes.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								在 Angular 的术语中,幂等的表达式应该总是返回*完全相同的东西*,直到某个依赖值发生改变。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								Dependent values should not change during a single turn of the event loop.
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								If an idempotent expression returns a string or a number, it returns the same string or number
							 
						 
					
						
							
								
									
										
										
										
											2017-03-31 12:23:16 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								when called twice in a row. If the expression returns an object (including an `array` ),
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								it returns the same object *reference*  when called twice in a row.
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								在单独的一次事件循环中,被依赖的值不应该改变。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  如果幂等的表达式返回一个字符串或数字,连续调用它两次,也应该返回相同的字符串或数字。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  如果幂等的表达式返回一个对象(包括`Date` 或`Array` ),连续调用它两次,也应该返回同一个对象的*引用*。
							 
						 
					
						
							
								
									
										
										
										
											2017-07-30 22:11:36 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-10 16:51:13 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< hr / >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								{@a  template-statements}
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								## Template statements
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								## 模板语句
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								A template **statement**  responds to an **event**  raised by a binding target
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								such as an element, component, or directive.
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 15:36:40 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								You'll see template statements in the [event binding ](guide/template-syntax#event-binding ) section,
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								appearing in quotes to the right of the `=`   symbol as in `(event)="statement"` .
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								模板**语句**用来响应由绑定目标(如 HTML 元素、组件或指令)触发的**事件**。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								模板语句将在[事件绑定 ](guide/template-syntax#event-binding )一节看到,它出现在`=` 号右侧的引号中,就像这样:`(event)="statement"` 。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.html"  region = "context-component-statement"  title = "src/app/app.component.html"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								A template statement *has a side effect* .
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								That's the whole point of an event.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								It's how you update application state from user action.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								模板语句*有副作用*。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								这是事件处理的关键。因为我们要根据用户的输入更新应用状态。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Responding to events is the other side of Angular's "unidirectional data flow".
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								You're free to change anything, anywhere, during this turn of the event loop.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								响应事件是 Angular 中“单向数据流”的另一面。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								    在一次事件循环中,可以随意改变任何地方的任何东西。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-31 12:23:16 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								Like template expressions, template *statements*  use a language that looks like JavaScript.
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								The template statement parser differs from the template expression parser and
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								specifically supports both basic assignment (`=` ) and chaining expressions
							 
						 
					
						
							
								
									
										
										
										
											2017-03-31 12:23:16 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								(with < code > ;< / code >  or < code > ,< / code > ).
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								和模板表达式一样,模板*语句*使用的语言也像 JavaScript。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  模板语句解析器和模板表达式解析器有所不同,特别之处在于它支持基本赋值 (`=` ) 和表达式链 (`;` 和`,` )。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-31 12:23:16 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								However, certain JavaScript syntax is not allowed:
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								然而,某些 JavaScript 语法仍然是不允许的:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-31 12:23:16 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								*  < code > new</ code >  
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  `new` 运算符
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								*  increment and decrement operators, `++`  and `--`  
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  自增和自减运算符:`++` 和`--` 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								*  operator assignment, such as `+=`  and `-=`  
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  操作并赋值,例如`+=` 和`-=` 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								*  the bitwise operators `|`  and `&`  
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  位操作符`|` 和`&` 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 15:36:40 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								*  the [template expression operators ](guide/template-syntax#expression-operators ) 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								  [模板表达式运算符 ](guide/template-syntax#expression-operators )
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								### Statement context
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								### 语句上下文
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								As with expressions, statements can refer only to what's in the statement context
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								such as an event handling method of the component instance.
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								和表达式中一样,语句只能引用语句上下文中 —— 通常是正在绑定事件的那个**组件实例**。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								The *statement context*  is typically the component instance.
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The *deleteHero*  in `(click)="deleteHero()"`  is a method of the data-bound component.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								典型的*语句上下文*就是当前组件的实例。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								`(click)="deleteHero()"` 中的*deleteHero*就是这个数据绑定组件上的一个方法。 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.html"  region = "context-component-statement"  title = "src/app/app.component.html"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The statement context may also refer to properties of the template's own context.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								In the following examples, the template `$event`  object,
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 15:36:40 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								a [template input variable ](guide/template-syntax#template-input-variable ) (`let hero` ),
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								and a [template reference variable ](guide/template-syntax#ref-vars ) (`#heroForm` )
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								are passed to an event handling method of the component.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								语句上下文可以引用模板自身上下文中的属性。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								在下面的例子中,就把模板的`$event` 对象、[模板输入变量 ](guide/template-syntax#template-input-variable ) (`let hero` )和[模板引用变量 ](guide/template-syntax#ref-vars ) (`#heroForm` )传给了组件中的一个事件处理器方法。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.html"  region = "context-var-statement"  title = "src/app/app.component.html"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Template context names take precedence over component context names.
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								In `deleteHero(hero)`  above, the `hero`  is the template input variable,
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								not the component's `hero`  property.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								模板上下文中的变量名的优先级高于组件上下文中的变量名。在上面的`deleteHero(hero)` 中,`hero` 是一个模板输入变量,而不是组件中的`hero` 属性。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								Template statements cannot refer to anything in the global namespace. They
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								can't refer to `window`  or `document` .
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								They can't call `console.log`  or `Math.max` .
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								模板语句不能引用全局命名空间的任何东西。比如不能引用`window`  或 `document` ,也不能调用`console.log` 或`Math.max` 。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								### Statement guidelines
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								### 语句指南
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								As with expressions, avoid writing complex template statements.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								A method call or simple property assignment should be the norm.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								和表达式一样,避免写复杂的模板语句。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								常规是函数调用或者属性赋值。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Now that you have a feel for template expressions and statements,
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								you're ready to learn about the varieties of data binding syntax beyond interpolation.
							 
						 
					
						
							
								
									
										
										
										
											2017-07-30 17:40:53 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								现在,对模板表达式和语句有了一点感觉了吧。
							 
						 
					
						
							
								
									
										
										
										
											2017-07-30 17:40:53 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								  除插值表达式外,还有各种各样的数据绑定语法,是学习它们是时候了。
							 
						 
					
						
							
								
									
										
										
										
											2017-08-26 17:56:20 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								  
							 
						 
					
						
							
								
									
										
										
										
											2017-04-10 16:51:13 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< hr / >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								{@a  binding-syntax}
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								## Binding syntax: An overview
  
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								## 绑定语法:概览
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								Data binding is a mechanism for coordinating what users see, with application data values.
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								  While you could push values to and pull values from HTML,
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  the application is easier to write, read, and maintain if you turn these chores over to a binding framework.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  You simply declare bindings between binding sources and target HTML elements and let the framework do the work.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								数据绑定是一种机制,用来协调用户所见和应用数据。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  虽然我们能往 HTML 推送值或者从 HTML 拉取值,
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  但如果把这些琐事交给数据绑定框架处理,
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  应用会更容易编写、阅读和维护。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  只要简单地在绑定源和目标 HTML 元素之间声明绑定,框架就会完成这项工作。
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								Angular provides many kinds of data binding.
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								This guide covers most of them, after a high-level view of Angular data binding and its syntax.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								Angular 提供了各种各样的数据绑定,本章将逐一讨论。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								不过我们要先从高层视角来看看 Angular 数据绑定及其语法。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Binding types can be grouped into three categories distinguished by the direction of data flow:
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								from the _source-to-view_ , from _view-to-source_ , and in the two-way sequence: _view-to-source-to-view_ :
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								绑定的类型可以根据数据流的方向分成三类:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								*从数据源到视图*、*从视图到数据源*以及双向的*从视图到数据源再到视图*。
							 
						 
					
						
							
								
									
										
										
										
											2017-07-30 00:03:22 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								  
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-30 20:04:18 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-30 00:03:22 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< table  >  
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								  < tr > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								    < th > 
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								      < p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								        Data direction
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < / p > 
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								      < p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								        数据方向
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < / p > 
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								    < / th > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								    < th > 
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								      < p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								        Syntax
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < / p > 
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								      < p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								        语法
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < / p > 
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								    < / th > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								    < th > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								      < p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								        Type
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < / p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								        绑定类型
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < / p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								    < / th > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  < / tr > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  < tr > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								    < td > 
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								        One-way
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < / p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								        单向
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < / p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								        from data source
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < / p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								        从数据源
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < / p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								        to view target
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < / p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								        到视图目标
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < / p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								    < / td > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								    < td > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < code-example > 
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								        {{expression}}
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								        [target]="expression"
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								        bind-target="expression"
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < / code-example > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								    < / td > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								    < td > 
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								        Interpolation
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < / p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								        插值表达式
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < / p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								        Property
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < / p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								        Attribute
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < / p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								        Class
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < / p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								        类
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < / p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								        Style
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < / p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								        样式
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < / p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								    < / td > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-30 00:03:22 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								  < / tr >   < tr > 
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < td > 
							 
						 
					
						
							
								
									
										
										
										
											2017-07-30 00:03:22 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< p >         One-way< / p >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								      < p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								        单向
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < / p > 
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-30 00:03:22 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								      < p > from view target< / p > 
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								        从视图目标
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < / p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-30 00:03:22 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								      < p > to data source
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								      < / p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								        到数据源
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < / p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								    < / td > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < td > 
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								        < code-example > 
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								          (target)="statement"
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								          on-target="statement"
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								        < / code-example > 
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < / td > 
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-30 00:03:22 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								      < td > < p > 
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								        Event
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								      < / p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								        事件
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < / p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								    < / td > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								    < / tr > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								    < tr > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-30 00:03:22 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								      < td > < p > 
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								        Two-way
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								      < / p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								        双向
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < / p > 
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								    < / td > 
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < td > 
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								        < code-example > 
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								          [(target)]="expression"
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								          bindon-target="expression"
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								        < / code-example > 
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < / td > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-30 00:03:22 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								      < td > < p > 
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								        Two-way
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								      < / p > 
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-30 00:03:22 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								    < p > 
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								        双向
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < / p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								    < / td > 
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  < / tr > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								< / table >  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< div  class = "alert is-important" >  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								译注:由于 HTML attribute 和 DOM property 在中文中都被翻译成了“属性”,无法区分,
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								而接下来的部分重点是对它们进行比较。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								我们无法改变历史,因此,在本章的翻译中,保留了它们的英文形式,不加翻译,以免混淆。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
										 
							
							
								本章中,如果提到“属性”的地方,一定是指 property, 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								但在其它章节中,为简单起见,凡是能通过上下文明显区分开的,就仍统一译为“属性”,
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								区分不明显的,会加注英文。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								< / div >  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Binding types other than interpolation have a **target name**  to the left of the equal sign,
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								either surrounded by punctuation (`[]` , `()` ) or preceded by a prefix (`bind-` , `on-` , `bindon-` ).
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
										 
							
							
								除了插值表达式之外的绑定类型,在等号左边是**目标名**, 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  无论是包在括号中 (`[]` 、`()` ) 还是用前缀形式 (`bind-` 、`on-` 、`bindon-` ) 。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The target name is the name of a _property_ . It may look like the name of an _attribute_  but it never is.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								To appreciate the difference, you must develop a new way to think about template HTML.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
										 
							
							
								这个目标名就是*属性( ) ( ) 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								要理解它们的不同点,我们必须尝试用另一种方式来审视模板中的 HTML。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								### A new mental model
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								### 新的思维模型
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								With all the power of data binding and the ability to extend the HTML vocabulary
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								with custom markup, it is tempting to think of template HTML as *HTML Plus* .
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								数据绑定的威力和允许用自定义标记扩展 HTML 词汇的能力,容易误导我们把模板 HTML 当成 *HTML+* 。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								It really *is*  HTML Plus.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								But it's also significantly different than the HTML you're used to.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								It requires a new mental model.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								它其实*就是* HTML+。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								但它也跟我们熟悉的 HTML 有着显著的不同。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								我们需要一种新的思维模型。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								In the normal course of HTML development, you create a visual structure with HTML elements, and
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								you modify those elements by setting element attributes with string constants.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								在正常的 HTML 开发过程中,我们使用 HTML 元素创建视觉结构,
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								通过把字符串常量设置到元素的 attribute 来修改那些元素。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.html"  region = "img+button"  title = "src/app/app.component.html"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								You still create a structure and initialize attribute values this way in Angular templates.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								在 Angular 模板中,我们仍使用同样的方式来创建结构和初始化 attribute 值。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Then you learn to create new elements with components that encapsulate HTML
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								and drop them into  templates as if they were native HTML elements.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								然后,用封装了 HTML 的组件创建新元素,并把它们当作原生 HTML 元素在模板中使用。
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.html"  region = "hero-detail-1"  title = "src/app/app.component.html"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								That's HTML Plus.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								这就是HTML+。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Then you learn about data binding. The first binding you meet might look like this:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								现在开始学习数据绑定。我们碰到的第一种数据绑定是这样的:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.html"  region = "disabled-button-1"  title = "src/app/app.component.html"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								You'll get to that peculiar bracket notation in a moment. Looking beyond it,
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								your intuition suggests that you're binding to the button's `disabled`  attribute and setting
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								it to the current value of the component's `isUnchanged`  property.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								过会儿再认识那个怪异的方括号记法。直觉告诉我们,我们正在绑定按钮的`disabled`  attribute。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  并把它设置为组件的`isUnchanged` 属性的当前值。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Your intuition is incorrect! Your everyday HTML mental model is misleading.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								In fact, once you start data binding, you are no longer working with HTML *attributes* . You aren't setting attributes.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								You are setting the *properties*  of DOM elements, components, and directives.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								但我们的直觉是错的!日常的 HTML 思维模式在误导我们。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								实际上,一旦开始数据绑定,就不再跟 HTML attribute 打交道了。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
										 
							
							
								这里不是设置 attribute, 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-10 16:51:13 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< div  class = "l-sub-section" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								### HTML attribute vs. DOM property
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								### HTML attribute 与 DOM property 的对比
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The distinction between an HTML attribute and a DOM property is crucial to understanding how Angular binding works.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								要想理解 Angular 绑定如何工作,重点是搞清 HTML attribute 和 DOM property 之间的区别。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								**Attributes are defined by HTML. Properties are defined by the DOM (Document Object Model).**
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								**attribute 是由 HTML 定义的。property 是由 DOM (Document Object Model) 定义的。**
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								*  A few HTML attributes have 1:1 mapping to properties. `id`  is one example. 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								  少量 HTML attribute 和 property 之间有着 1:1 的映射,如`id` 。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								*  Some HTML attributes don't have corresponding properties. `colspan`  is one example. 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
										 
							
							
								  有些 HTML attribute 没有对应的 property, `colspan` 。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								*  Some DOM properties don't have corresponding attributes. `textContent`  is one example. 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
										 
							
							
								  有些 DOM property 没有对应的 attribute, `textContent` 。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								*  Many HTML attributes appear to map to properties ... but not in the way you might think! 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								  大量 HTML attribute看起来映射到了property…… 但却不像我们想的那样!
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								That last category is confusing until you grasp this general rule:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								最后一类尤其让人困惑…… 除非我们能理解这个普遍原则:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								**Attributes *initialize*  DOM properties and then they are done.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Property values can change; attribute values can't.**
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
										 
							
							
								**attribute *初始化*  DOM property, ; 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								For example, when the browser renders `<input type="text" value="Bob">` , it creates a
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								corresponding DOM node with a `value`  property *initialized*  to "Bob".
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								例如,当浏览器渲染`<input type="text" value="Bob">` 时,它将创建相应 DOM 节点,
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								其`value`  property 被*初始化为* “Bob”。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								When the user enters "Sally" into the input box, the DOM element `value`  *property*  becomes "Sally".
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								But the HTML `value`  *attribute*  remains unchanged as you discover if you ask the input element
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								about that attribute: `input.getAttribute('value')`  returns "Bob".
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
										 
							
							
								当用户在输入框中输入 “Sally” 时, `value`  *property*  变成了 “Sally”。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
										 
							
							
								但是这个 HTML `value`  *attribute*  保持不变。如果我们读取 input 元素的 attribute, : 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								`input.getAttribute('value') // 返回 "Bob"` 。 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The HTML attribute `value`  specifies the *initial*  value; the DOM `value`  property is the *current*  value.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
										 
							
							
								HTML attribute `value` 指定了*初始*值; `value`  property 是*当前*值。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The `disabled`  attribute is another peculiar example. A button's `disabled`  *property*  is
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								`false`  by default so the button is enabled. 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								When you add the `disabled`  *attribute* , its presence alone initializes the  button's `disabled`  *property*  to `true` 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								so the button is disabled.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								`disabled`  attribute 是另一个古怪的例子。按钮的`disabled`  *property*  是`false` ,因为默认情况下按钮是可用的。 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								当我们添加`disabled`  *attribute*  时,只要它出现了按钮的`disabled`  *property*  就初始化为`true` ,于是按钮就被禁用了。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Adding and removing the `disabled`  *attribute*  disables and enables the button. The value of the *attribute*  is irrelevant,
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								which is why you cannot enable a button by writing `<button disabled="false">Still Disabled</button>` .
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								添加或删除`disabled`  *attribute*会禁用或启用这个按钮。但 *attribute*  的值无关紧要,这就是我们为什么没法通过
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								`<button disabled="false">仍被禁用</button>` 这种写法来启用按钮。 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Setting the button's `disabled`  *property*   (say, with an Angular binding) disables or enables the button.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The value of the *property*  matters.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								设置按钮的`disabled`  *property* (如,通过 Angular 绑定)可以禁用或启用这个按钮。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								这就是 *property*  的价值。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								**The HTML attribute and the DOM property are not the same thing, even when they have the same name.**
							 
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
										 
							
							
								**就算名字相同, 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-10 16:51:13 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / div >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								This fact bears repeating:
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								这句话值得再强调一次:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								**Template binding works with *properties*  and *events* , not *attributes* .**
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								**模板绑定是通过 *property*  和*事件*来工作的,而不是 *attribute* 。**
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-10 16:51:13 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< div  class = "callout is-helpful" >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								< header >  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  A world without attributes
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								< / header >  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< header >  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  没有 attribute 的世界
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								< / header >  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								In the world of Angular, the only role of attributes is to initialize element and directive state.
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								When you write a data binding, you're dealing exclusively with  properties and eventsof the target object.
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								HTML attributes effectively disappear.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
										 
							
							
								在 Angular 的世界中, 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								当进行数据绑定时,只是在与元素和指令的 property 和事件打交道,而 attribute 就完全靠边站了。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-10 16:51:13 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / div >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								With this model firmly in mind, read on to learn about binding targets.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								把这个思维模型牢牢的印在脑子里,接下来,学习什么是绑定目标。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								### Binding targets
  
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								### 绑定目标
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The **target of a data binding**  is something in the DOM.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Depending on the binding type, the target can be an
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								(element | component | directive) property, an
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								(element | component | directive) event, or (rarely) an attribute name.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The following table summarizes:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								**数据绑定的目标**是 DOM 中的某些东西。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
										 
							
							
								这个目标可能是(元素 | 组件 | 指令的) ( 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								下面是的汇总表:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-30 20:04:18 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								< style >  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  td, th {vertical-align: top}
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								< / style >  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								< table  width = "100%" >  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  < col  width = "10%" > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  < / col > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  < col  width = "15%" > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  < / col > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  < col  width = "75%" > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  < / col > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  < tr > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								    < th > 
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								        Type
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < / p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								        绑定类型
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < / p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								    < / th > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								    < th > 
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								        Target
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < / p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								        目标
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < / p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								    < / th > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								    < th > 
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								        Examples
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < / p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								        范例
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < / p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								    < / th > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  < / tr > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  < tr > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								    < td > 
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								        Property
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < / p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								    < / td > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								    < td > 
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								        Element  property
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < / p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								        元素的 property
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < / p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								        Component  property
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < / p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								        组件的 property
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < / p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								        Directive  property
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < / p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								        指令的 property
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < / p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								    < / td > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								    < td > 
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								      < code-example  path = "template-syntax/src/app/app.component.html"  region = "property-binding-syntax-1"  title = "src/app/app.component.html"  linenums = "false" > 
							 
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								      < / code-example > 
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								    < / td > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  < / tr > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  < tr > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								    < td > 
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								        Event
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < / p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								        事件
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < / p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								    < / td > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								    < td > 
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								        Element  event
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < / p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								        元素的事件
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < / p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								        Component  event
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < / p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								        组件的事件
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < / p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								        Directive  event
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < / p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								        指令的事件
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < / p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								    < / td > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								    < td > 
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								      < code-example  path = "template-syntax/src/app/app.component.html"  region = "event-binding-syntax-1"  title = "src/app/app.component.html"  linenums = "false" > 
							 
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								      < / code-example > 
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								    < / td > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  < / tr > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  < tr > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								    < td > 
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								        Two-way
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < / p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								        双向
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < / p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								    < / td > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								    < td > 
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								        Event and property
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < / p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								        事件与 property
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < / p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								    < / td > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								    < td > 
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								      < code-example  path = "template-syntax/src/app/app.component.html"  region = "2-way-binding-syntax-1"  title = "src/app/app.component.html"  linenums = "false" > 
							 
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								      < / code-example > 
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								    < / td > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  < / tr > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  < tr > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								    < td > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      Attribute
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								    < / td > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								    < td > 
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								        Attribute (the  exception)
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < / p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
										 
							
							
								        attribute( ) 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < / p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								    < / td > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								    < td > 
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								      < code-example  path = "template-syntax/src/app/app.component.html"  region = "attribute-binding-syntax-1"  title = "src/app/app.component.html"  linenums = "false" > 
							 
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								      < / code-example > 
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								    < / td > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  < / tr > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  < tr > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								    < td > 
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								        Class
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < / p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								        CSS 类
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < / p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								    < / td > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								    < td > 
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								        < code > class< / code >  property
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < / p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								    < / td > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								    < td > 
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								      < code-example  path = "template-syntax/src/app/app.component.html"  region = "class-binding-syntax-1"  title = "src/app/app.component.html"  linenums = "false" > 
							 
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								      < / code-example > 
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								    < / td > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  < / tr > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  < tr > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								    < td > 
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								        Style
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < / p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								        样式
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < / p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								    < / td > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								    < td > 
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								        < code > style< / code >  property
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								      < / p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								    < / td > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								    < td > 
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								      < code-example  path = "template-syntax/src/app/app.component.html"  region = "style-binding-syntax-1"  title = "src/app/app.component.html"  linenums = "false" > 
							 
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								      < / code-example > 
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								    < / td > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  < / tr > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								< / table >  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								With this broad view in mind, you're ready to look at binding types in detail.
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								放开眼界,我们来看看每种绑定类型的具体情况。
							 
						 
					
						
							
								
									
										
										
										
											2017-07-30 22:11:36 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-10 16:51:13 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< hr / >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								{@a  property-binding}
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								## Property binding ( <span class="syntax">[property]</span> )
  
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								## 属性绑定 ( <span class="syntax">[属性名]</span> )
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Write a template **property binding**  to set a property of a view element.
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 15:36:40 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								The binding sets the property to the value of a [template expression ](guide/template-syntax#template-expressions ).
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								当要把视图元素的属性 (property) 设置为[模板表达式 ](guide/template-syntax#template-expressions )时,就要写模板的**属性 (property) 绑定**。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The most common property binding sets an element property to a component property value. An example is
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								binding the `src`  property of an image element to a component's `heroImageUrl`  property:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								最常用的属性绑定是把元素属性设置为组件属性的值。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
										 
							
							
								下面这个例子中, `src` 属性会被绑定到组件的`heroImageUrl` 属性上:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.html"  region = "property-binding-1"  title = "src/app/app.component.html"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Another example is disabling a button when the component says that it `isUnchanged` :
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								另一个例子是当组件说它`isUnchanged` (未改变)时禁用按钮:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.html"  region = "property-binding-2"  title = "src/app/app.component.html"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Another is setting a property of a directive:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								另一个例子是设置指令的属性:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.html"  region = "property-binding-3"  title = "src/app/app.component.html"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Yet another is setting the model property of a custom component (a great way
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								for parent and child components to communicate):
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								还有另一个例子是设置自定义组件的模型属性(这是父子组件之间通讯的重要途径):
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.html"  region = "property-binding-4"  title = "src/app/app.component.html"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								### One-way *in*
  
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								### 单向*输入*
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								People often describe property binding as *one-way data binding*  because it flows a value in one direction,
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								from a component's data property into a target element property.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								人们经常把属性绑定描述成*单向数据绑定*,因为值的流动是单向的,从组件的数据属性流动到目标元素的属性。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								You cannot use property binding to pull values *out*  of the target element.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								You can't bind to a property of the target element to _read_  it. You can only _set_  it.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								不能使用属性绑定来从目标元素拉取值,也不能绑定到目标元素的属性来读取它。只能设置它。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-10 16:51:13 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< div  class = "l-sub-section" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Similarly, you cannot use property binding to *call*  a method on the target element.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								也不能使用属性 绑定 来*调用*目标元素上的方法。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 15:36:40 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								If the element raises events, you can listen to them with an [event binding ](guide/template-syntax#event-binding ).
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								如果这个元素触发了事件,可以通过[事件绑定 ](guide/template-syntax#event-binding )来监听它们。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								If you must read a target element property or call one of its methods,
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								you'll need a different technique.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								See the API reference for
							 
						 
					
						
							
								
									
										
										
										
											2017-04-30 22:10:32 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								[ViewChild ](api/core/ViewChild ) and
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								[ContentChild ](api/core/ContentChild ).
							 
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								如果必须读取目标元素上的属性或调用它的某个方法,得用另一种技术。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								参见 API 参考手册中的
							 
						 
					
						
							
								
									
										
										
										
											2017-07-30 00:03:22 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								[ViewChild ](api/core/ViewChild ) 和
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								[ContentChild ](api/core/ContentChild )。
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-10 16:51:13 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / div >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								### Binding target
  
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								### 绑定目标  
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								An element property between enclosing square brackets identifies the target property. The target property in the following code is the image element's `src`  property.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								包裹在方括号中的元素属性名标记着目标属性。下列代码中的目标属性是 image 元素的`src` 属性。
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.html"  region = "property-binding-1"  title = "src/app/app.component.html"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Some people prefer the `bind-`  prefix alternative, known as the *canonical form* :
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
										 
							
							
								有些人喜欢用`bind-` 前缀的可选形式,并称之为*规范形式*: 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.html"  region = "property-binding-5"  title = "src/app/app.component.html"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								The target name is always the name of a property, even when it appears to be the name of something else.
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								You see `src`  and may think it's the name of an attribute. No. It's the name of an image element property.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								目标的名字总是 property 的名字。即使它看起来和别的名字一样。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
										 
							
							
								看到`src` 时,可能会把它当做 attribute。不! ! 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Element properties may be the more common targets,
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								but Angular looks first to see if the name is a property of a known directive,
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								as it is in the following example:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								元素属性可能是最常见的绑定目标,但 Angular 会先去看这个名字是否是某个已知指令的属性名,就像下面的例子中一样:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.html"  region = "property-binding-3"  title = "src/app/app.component.html"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-10 16:51:13 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< div  class = "l-sub-section" >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 15:36:40 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								Technically, Angular is matching the name to a directive [input ](guide/template-syntax#inputs-outputs ),
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								one of the property names listed in the directive's `inputs`  array or a property decorated with `@Input()` .
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								Such inputs map to the directive's own properties.
							 
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
										 
							
							
								严格来说, 输入属性 ](guide/template-syntax#inputs-outputs )的名字。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								这个名字是指令的`inputs` 数组中所列的名字,或者是带有`@Input()` 装饰器的属性。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								这些输入属性被映射为指令自己的属性。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-10 16:51:13 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / div >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								If the name fails to match a property of a known directive or element, Angular reports an “unknown directive” error.
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
										 
							
							
								如果名字没有匹配上已知指令或元素的属性, 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								### Avoid side effects
  
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								### 消除副作用
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								As mentioned previously, evaluation of a template expression should have no visible side effects.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The expression language itself does its part to keep you safe.
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								You can't assign a value to anything in a property binding expression nor use the increment and decrement operators.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								正如以前讨论过的,模板表达式的计算不能有可见的副作用。表达式语言本身可以提供一部分安全保障。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  不能在属性绑定表达式中对任何东西赋值,也不能使用自增、自减运算符。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								Of course, the expression might invoke a property or method that has side effects.
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								  Angular has no way of knowing that or stopping you.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								当然,表达式可能会调用具有副作用的属性或方法。但 Angular 没法知道这一点,也没法阻止我们。
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The expression could call something like `getFoo()` . Only you know what `getFoo()`  does.
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								If `getFoo()`  changes something and you happen to be binding to that something, you risk an unpleasant experience.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Angular may or may not display the changed value. Angular may detect the change and throw a warning error.
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								In general, stick to data properties and to methods that return values and do no more.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								表达式中可以调用像`getFoo()` 这样的方法。只有我们知道`getFoo()` 干了什么。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								如果`getFoo()` 改变了某个东西,恰好又绑定到个这个东西,我们就可能把自己坑了。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Angular 可能显示也可能不显示变化后的值。Angular 还可能检测到变化,并抛出警告型错误。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								一般建议是,只绑定数据属性和那些只返回值而不做其它事情的方法。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								### Return the proper type
  
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								### 返回恰当的类型
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The template expression should evaluate to the type of value expected by the target property.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Return a string if the target property expects a string.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Return a number if the target property expects a number.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Return an object if the target property expects an object.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								模板表达式应该返回目标属性所需类型的值。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								如果目标属性想要个字符串,就返回字符串。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								如果目标属性想要个数字,就返回数字。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								如果目标属性想要个对象,就返回对象。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The `hero`  property of the `HeroDetail`  component expects a `Hero`  object, which is exactly what you're sending in the property binding:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								`HeroDetail` 组件的`hero` 属性想要一个`Hero` 对象,那就在属性绑定中精确地给它一个`Hero` 对象: 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.html"  region = "property-binding-4"  title = "src/app/app.component.html"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								### Remember the brackets
  
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								### 别忘了方括号
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The brackets tell Angular to evaluate the template expression.
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								If you omit the brackets, Angular treats the string as a constant
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								and *initializes the target property*  with that string.
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								It does *not*  evaluate the string!
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								方括号告诉 Angular 要计算模板表达式。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
										 
							
							
								如果忘了加方括号, 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								它*不会*计算这个字符串。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Don't make the following mistake:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								不要出现这样的失误:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.html"  region = "property-binding-6"  title = "src/app/app.component.html"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								{@a  one-time-initialization}
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								### One-time string initialization
  
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								### 一次性字符串初始化
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								You *should*  omit the brackets when all of the following are true:
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								当满足下列条件时,*应该*省略括号:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								*  The target property accepts a string value. 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  目标属性接受字符串值。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								*  The string is a fixed value that you can bake into the template. 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  字符串是个固定值,可以直接合并到模块中。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								*  This initial value never changes. 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								  这个初始值永不改变。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								You routinely initialize attributes this way in standard HTML, and it works
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								just as well for directive and component property initialization.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The following example initializes the `prefix`  property of the `HeroDetailComponent`  to a fixed string,
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								not a template expression. Angular sets it and forgets about it.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
										 
							
							
								我们经常这样在标准 HTML 中用这种方式初始化 attribute, 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
										 
							
							
								下面这个例子把`HeroDetailComponent` 的`prefix` 属性初始化为固定的字符串, 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.html"  region = "property-binding-7"  title = "src/app/app.component.html"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The `[hero]`  binding, on the other hand, remains a live binding to the component's `currentHero`  property.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								作为对比,`[hero]` 绑定是组件的`currentHero` 属性的活绑定,它会一直随着更新。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-30 22:10:32 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								{@a  property-binding-or-interpolation}
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								### Property binding or interpolation?
  
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								### 属性绑定还是插值表达式?
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								You often have a choice between interpolation and property binding.
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The following binding pairs do the same thing:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								我们通常得在插值表达式和属性绑定之间做出选择。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								下列这几对绑定做的事情完全相同:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.html"  region = "property-binding-vs-interpolation"  title = "src/app/app.component.html"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								_Interpolation_ is a convenient alternative to _property binding_  in many cases.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								在多数情况下,插值表达式是更方便的备选项。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
										 
							
							
								实际上, , 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								When rendering data values as strings, there  is no technical reason to prefer one form to the other.
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								You lean toward readability, which tends to favor interpolation.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								You suggest establishing coding style rules and choosing the form that
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								both conforms to the rules and feels most natural for the task at hand.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								当要渲染的数据类型是字符串时,没有技术上的理由证明哪种形式更好。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								我们倾向于可读性,所以倾向于插值表达式。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								建议建立代码风格规则,选择一种形式,
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								这样,既遵循了规则,又能让手头的任务做起来更自然。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								When setting an element property to a non-string data value, you must use _property binding_ .
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								但数据类型不是字符串时,就必须使用*属性绑定*了。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								#### Content security
  
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								#### 内容安全
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Imagine the following *malicious content* .
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								假设下面的*恶意内容*
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.ts"  region = "evil-title"  title = "src/app/app.component.ts"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Fortunately, Angular data binding is on alert for dangerous HTML.
							 
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								It [*sanitizes* ](guide/security#sanitization-and-security-contexts ) the values before displaying them.
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								It **will not**  allow HTML with script tags to leak into the browser, neither with interpolation
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								nor property binding.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
										 
							
							
								幸运的是, 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								在显示它们之前,它对内容先进行*消毒*。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								不管是插值表达式还是属性绑定,都**不会**允许带有 script 标签的 HTML 泄漏到浏览器中。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.html"  region = "property-binding-vs-interpolation-sanitization"  title = "src/app/app.component.html"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Interpolation handles the script tags differently than property binding but both approaches render the
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								content harmlessly.
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								插值表达式处理 script 标签与属性绑定有所不同,但是二者都只渲染没有危害的内容。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-30 20:04:18 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-05-09 23:53:32 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< figure >  
						 
					
						
							
								
									
										
										
										
											2017-05-11 21:44:22 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								  < img  src = 'generated/images/guide/template-syntax/evil-title.png'  alt = "evil title made safe" > 
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								< / figure >  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-31 08:48:00 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< a  href = " #top -of-page" > 回到顶部</ a >  
						 
					
						
							
								
									
										
										
										
											2017-03-30 20:04:18 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-10 16:51:13 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< hr / >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								{@a  other-bindings}
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								## Attribute, class, and style bindings
  
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								## attribute、class 和 style 绑定
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The template syntax provides specialized one-way bindings for scenarios less well suited to property binding.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								模板语法为那些不太适合使用属性绑定的场景提供了专门的单向数据绑定形式。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								### Attribute binding
  
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								### attribute 绑定
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								You can set the value of an attribute directly with an **attribute binding** .
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								可以通过**attribute 绑定**来直接设置 attribute 的值。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-10 16:51:13 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< div  class = "l-sub-section" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								This is the only exception to the rule that a binding sets a target property.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								This is the only binding that creates and sets an attribute.
							 
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								这是“绑定到目标属性 (property)”这条规则中唯一的例外。这是唯一的能创建和设置 attribute 的绑定形式。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-10 16:51:13 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / div >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								This guide stresses repeatedly that setting an element property with a property binding
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								is always preferred to setting the attribute with a string. Why does Angular offer attribute binding?
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								本章中,通篇都在说通过属性绑定来设置元素的属性总是好于用字符串设置 attribute。为什么 Angular 还提供了 attribute 绑定呢?
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								**You must use attribute binding when there is no element property to bind.**
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								**因为当元素没有属性可绑的时候,就必须使用 attribute 绑定。**
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Consider the [ARIA ](https://developer.mozilla.org/en-US/docs/Web/Accessibility/ARIA ),
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								[SVG ](https://developer.mozilla.org/en-US/docs/Web/SVG ), and
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								table span attributes. They are pure attributes.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								They do not correspond to element properties, and they do not set element properties.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								There are no property targets to bind to.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
										 
							
							
								考虑 [ARIA ](https://developer.mozilla.org/en-US/docs/Web/Accessibility/ARIA ), 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  [SVG ](https://developer.mozilla.org/en-US/docs/Web/SVG ) 和 table 中的 colspan/rowspan 等 attribute。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
										 
							
							
								  它们是纯粹的 attribute, 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								This fact becomes painfully obvious when you write something like this.
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								如果想写出类似下面这样的东西,现状会令我们痛苦:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-30 20:04:18 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  language = "html" >  
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								  < tr> < td colspan="{{1 + 1}}"> Three-Four< /td> < /tr> 
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								And you get this error:
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								会得到这个错误:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-30 20:04:18 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  format = "nocode" >  
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								  Template parse errors:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  Can't bind to 'colspan' since it isn't a known native property
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								  (模板解析错误:不能绑定到 'colspan',因为它不是已知的原生属性)
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								As the message says, the `<td>`  element does not have a `colspan`  property.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								It has the "colspan" *attribute* , but
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								interpolation and property binding can set only *properties* , not attributes.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								正如提示中所说,`<td>` 元素没有`colspan` 属性。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  但是插值表达式和属性绑定只能设置*属性*,不能设置 attribute。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								You need attribute bindings to create and bind to such attributes.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								我们需要 attribute 绑定来创建和绑定到这样的 attribute。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Attribute binding syntax resembles property binding.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Instead of an element property between brackets, start with the prefix ** `attr` **,
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								followed by a dot (`.` ) and the name of the attribute.
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								You then set the attribute value, using an expression that resolves to a string.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								attribute 绑定的语法与属性绑定类似。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  但方括号中的部分不是元素的属性名,而是由**`attr` **前缀,一个点 (`.` ) 和 attribute 的名字组成。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  可以通过值为字符串的表达式来设置 attribute 的值。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Bind `[attr.colspan]`  to a calculated value:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								这里把`[attr.colspan]` 绑定到一个计算值:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.html"  region = "attrib-binding-colspan"  title = "src/app/app.component.html"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Here's how the table renders:
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								这里是表格渲染出来的样子:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								< table  border = "1px" >  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  < tr > < td  colspan = "2" > One-Two< / td > < / tr > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  < tr > < td > Five< / td > < td > Six< / td > < / tr > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								 < / table > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								One of the primary use cases for attribute binding
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								is to set ARIA attributes, as in this example:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
										 
							
							
								attribute 绑定的主要用例之一是设置 ARIA attribute( : , ) , 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								就像这个例子中一样:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.html"  region = "attrib-binding-aria"  title = "src/app/app.component.html"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-30 22:11:36 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-10 16:51:13 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< hr / >  
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								### Class binding
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								### CSS 类绑定
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								You can add and remove CSS class names from an element's `class`  attribute with
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								a **class binding** .
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								借助 **CSS 类绑定** ,可以从元素的`class`  attribute 上添加和移除 CSS 类名。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Class binding syntax resembles property binding.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Instead of an element property between brackets, start with the prefix `class` ,
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								optionally followed by a dot (`.` ) and the name of a CSS class: `[class.class-name]` .
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								CSS 类绑定绑定的语法与属性绑定类似。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								但方括号中的部分不是元素的属性名,而是由**`class` **前缀,一个点 (`.` )和 CSS 类的名字组成,
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								其中后两部分是可选的。形如:`[class.class-name]` 。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The following examples show how to add and remove the application's "special" class
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								with class bindings.  Here's how to set the attribute without binding:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								下列例子示范了如何通过 CSS 类绑定来添加和移除应用的 "special" 类。不用绑定直接设置 attribute 时是这样的:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.html"  region = "class-binding-1"  title = "src/app/app.component.html"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								You can replace that with a binding to a string of the desired class names; this is an all-or-nothing, replacement binding.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								可以把它改写为绑定到所需 CSS 类名的绑定;这是一个或者全有或者全无的替换型绑定。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								(译注:即当 badCurly 有值时 class 这个 attribute 设置的内容会被完全覆盖)
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.html"  region = "class-binding-2"  title = "src/app/app.component.html"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Finally, you can bind to a specific class name.
							 
						 
					
						
							
								
									
										
										
										
											2017-03-31 12:23:16 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								Angular adds the class when the template expression evaluates to truthy.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								It removes the class when the expression is falsy.
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								最后,可以绑定到特定的类名。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
										 
							
							
								  当模板表达式的求值结果是真值时, 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-30 20:04:18 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.html"  region = "class-binding-3"  title = "src/app/app.component.html"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-10 16:51:13 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< div  class = "l-sub-section" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								While this is a fine way to toggle a single class name,
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 15:36:40 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								the [NgClass directive ](guide/template-syntax#ngClass ) is usually preferred when managing multiple class names at the same time.
							 
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								虽然这是切换单一类名的好办法,但我们通常更喜欢使用 [NgClass指令 ](guide/template-syntax#ngClass ) 来同时管理多个类名。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-10 16:51:13 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / div >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-10 16:51:13 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< hr / >  
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								### Style binding
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								### 样式绑定
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								You can set inline styles with a **style binding** .
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								通过**样式绑定**,可以设置内联样式。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Style binding syntax resembles property binding.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Instead of an element property between brackets, start with the prefix `style` ,
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								followed by a dot (`.` ) and the name of a CSS style property: `[style.style-property]` .
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								样式绑定的语法与属性绑定类似。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								但方括号中的部分不是元素的属性名,而由**`style` **前缀,一个点 (`.` )和 CSS 样式的属性名组成。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								形如:`[style.style-property]` 。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.html"  region = "style-binding-1"  title = "src/app/app.component.html"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								Some style binding styles have a unit extension. The following example conditionally sets the font size in  “em” and “%” units.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								有些样式绑定中的样式带有单位。在这里,以根据条件用 “em” 和 “%” 来设置字体大小的单位。
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.html"  region = "style-binding-2"  title = "src/app/app.component.html"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-10 16:51:13 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< div  class = "l-sub-section" >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								While this is a fine way to set a single style,
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 15:36:40 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								the [NgStyle directive ](guide/template-syntax#ngStyle ) is generally preferred when setting several inline styles at the same time.
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								虽然这是设置单一样式的好办法,但我们通常更喜欢使用 [NgStyle指令 ](guide/template-syntax#ngStyle ) 来同时设置多个内联样式。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-10 16:51:13 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / div >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-10 16:51:13 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< div  class = "l-sub-section" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Note that a _style property_  name can be written in either
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								[dash-case ](guide/glossary#dash-case ), as shown above, or
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								[camelCase ](guide/glossary#camelcase ), such as `fontSize` .
							 
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
										 
							
							
								注意, 中线命名法 ](guide/glossary#dash-case ),像上面的一样
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								    也可以用[驼峰式命名法 ](guide/glossary#camelcase ),如`fontSize` 。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-10 16:51:13 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / div >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-10 16:51:13 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< hr / >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								{@a  event-binding}
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								## Event binding  ( <span class="syntax">(event)</span> )
  
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								## 事件绑定  ( <span class="syntax">(事件名)</span> )
  
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The bindings directives you've met so far flow data in one direction: **from a component to an element** .
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								前面遇到的绑定的数据流都是单向的:**从组件到元素**。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Users don't just stare at the screen. They enter text into input boxes. They pick items from lists.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								They click buttons. Such user actions may result in a flow of data in the opposite direction:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								**from an element to a component**.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								但用户不会只盯着屏幕看。他们会在输入框中输入文本。他们会从列表中选取条目。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								他们会点击按钮。这类用户动作可能导致反向的数据流:*从元素到组件*。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The only way to know about a user action is to listen for certain events such as
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								keystrokes, mouse movements, clicks, and touches.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								You declare your interest in user actions through Angular event binding.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								知道用户动作的唯一方式是监听某些事件,如按键、鼠标移动、点击和触摸屏幕。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								可以通过 Angular 事件绑定来声明对哪些用户动作感兴趣。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								Event binding syntax consists of a **target event**  name
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								within parentheses on the left of an equal sign, and a quoted
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 15:36:40 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								[template statement ](guide/template-syntax#template-statements ) on the right.
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								The following event binding listens for the button's click events, calling
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								the component's `onSave()`  method whenever a click occurs:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								事件绑定语法由等号左侧带圆括号的**目标事件**和右侧引号中的[模板语句 ](guide/template-syntax#template-statements )组成。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								下面事件绑定监听按钮的点击事件。每当点击发生时,都会调用组件的`onSave()` 方法。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.html"  region = "event-binding-1"  title = "src/app/app.component.html"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								### Target event
  
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								### 目标事件
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								A **name between parentheses**  —  for example, `(click)`  — 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								identifies the target event. In the following example, the target is the button's click event.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								**圆括号中的名称** —— 比如`(click)`  —— 标记出目标事件。在下面例子中,目标是按钮的 click 事件。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.html"  region = "event-binding-1"  title = "src/app/app.component.html"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Some people prefer the `on-`  prefix alternative, known as the **canonical form** :
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
										 
							
							
								有些人更喜欢带`on-` 前缀的备选形式,称之为**规范形式**: 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.html"  region = "event-binding-2"  title = "src/app/app.component.html"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Element events may be the more common targets, but Angular looks first to see if the name matches an event property
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								of a known directive, as it does in the following example:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								元素事件可能是更常见的目标,但 Angular 会先看这个名字是否能匹配上已知指令的事件属性,就像下面这个例子:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.html"  region = "event-binding-3"  title = "src/app/app.component.html"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-10 16:51:13 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< div  class = "l-sub-section" >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The `myClick`  directive is further described in the section
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 15:36:40 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								on [aliasing input/output properties ](guide/template-syntax#aliasing-io ).
							 
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								更多关于该`myClick` 指令的解释,见[给输入/输出属性起别名 ](guide/template-syntax#aliasing-io )。
							 
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-10 16:51:13 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / div >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								If the name fails to match an element event or an output property of a known directive,
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Angular reports an “unknown directive” error.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
										 
							
							
								如果这个名字没能匹配到元素事件或已知指令的输出属性, 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								### *$event* and event handling statements
  
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								### *$event* 和事件处理语句
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								In an event binding, Angular sets up an event handler for the target event.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
										 
							
							
								在事件绑定中, 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								When the event is raised, the handler executes the template statement.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The template statement typically involves a receiver, which performs an action
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								in response to the event, such as storing a value from the HTML control
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								into a model.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								当事件发生时,这个处理器会执行模板语句。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								典型的模板语句通常涉及到响应事件执行动作的接收器,例如从 HTML 控件中取得值,并存入模型。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The binding conveys information about the event, including data values, through
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								an **event object named `$event`** .
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								绑定会通过**名叫`$event` 的事件对象**传递关于此事件的信息(包括数据值)。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The shape of the event object is determined by the target event.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								If the target event is a native DOM element event, then `$event`  is a
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								[DOM event object ](https://developer.mozilla.org/en-US/docs/Web/Events ),
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								with properties such as `target`  and `target.value` .
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								事件对象的形态取决于目标事件。如果目标事件是原生 DOM 元素事件,
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								`$event` 就是 [DOM事件对象 ](https://developer.mozilla.org/en-US/docs/Web/Events ),它有像`target` 和`target.value` 这样的属性。 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Consider this example:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								考虑这个范例:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.html"  region = "without-NgModel"  title = "src/app/app.component.html"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								This code sets the input box `value`  property by binding to the `name`  property.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								To listen for changes to the value, the code binds to the input box's `input`  event.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								When the user makes changes, the `input`  event is raised, and the binding executes
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								the statement within a context that includes the DOM event object, `$event` .
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								上面的代码在把输入框的`value` 属性绑定到`firstName` 属性。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								要监听对值的修改,代码绑定到输入框的`input` 事件。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								当用户造成更改时,`input` 事件被触发,并在包含了 DOM 事件对象 (`$event` ) 的上下文中执行这条语句。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								To update the `name`  property, the changed text is retrieved by following the path `$event.target.value` .
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								要更新`firstName` 属性,就要通过路径`$event.target.value` 来获取更改后的值。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								If the event belongs to a directive (recall that components are directives),
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								`$event`  has whatever shape the directive decides to produce. 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								如果事件属于指令(回想一下,组件是指令的一种),那么`$event` 具体是什么由指令决定。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								{@a  eventemitter}
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								{@a  custom-event}
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								### Custom events with <span class="syntax">EventEmitter</span>
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								### 使用 <span class="syntax">EventEmitter</span> 实现自定义事件
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-30 22:10:32 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								Directives typically raise custom events with an Angular [EventEmitter ](api/core/EventEmitter ).
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The directive creates an `EventEmitter`  and exposes it as a property.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The directive calls `EventEmitter.emit(payload)`  to fire an event, passing in a message payload, which can be anything.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Parent directives listen for the event by binding to this property and accessing the payload through the `$event`  object.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-30 12:32:56 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								通常,指令使用 Angular [EventEmitter ](api/core/EventEmitter ) 来触发自定义事件。
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								指令创建一个`EventEmitter` 实例,并且把它作为属性暴露出来。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								指令调用`EventEmitter.emit(payload)` 来触发事件,可以传入任何东西作为消息载荷。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								父指令通过绑定到这个属性来监听事件,并通过`$event` 对象来访问载荷。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Consider a `HeroDetailComponent`  that presents hero information and responds to user actions.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Although the `HeroDetailComponent`  has a delete button it doesn't know how to delete the hero itself.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The best it can do is raise an event reporting the user's delete request.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								假设`HeroDetailComponent` 用于显示英雄的信息,并响应用户的动作。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								虽然`HeroDetailComponent` 包含删除按钮,但它自己并不知道该如何删除这个英雄。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								最好的做法是触发事件来报告“删除用户”的请求。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								Here are the pertinent excerpts from that `HeroDetailComponent` :
							 
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
										 
							
							
								下面的代码节选自`HeroDetailComponent` : 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/hero-detail.component.ts"  linenums = "false"  title = "src/app/hero-detail.component.ts (template)"  region = "template-1" >  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/hero-detail.component.ts"  linenums = "false"  title = "src/app/hero-detail.component.ts (deleteRequest)"  region = "deleteRequest" >  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								The component defines a `deleteRequest`  property that returns an `EventEmitter` .
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								When the user clicks *delete* , the component invokes the `delete()`  method,
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								telling the `EventEmitter`  to emit a `Hero`  object.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								组件定义了`deleteRequest` 属性,它是`EventEmitter` 实例。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								当用户点击*删除*时,组件会调用`delete()` 方法,让`EventEmitter` 发出一个`Hero` 对象。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Now imagine a hosting parent component that binds to the `HeroDetailComponent` 's `deleteRequest`  event.
							 
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								现在,假设有个宿主的父组件,它绑定了`HeroDetailComponent` 的`deleteRequest` 事件。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.html"  linenums = "false"  title = "src/app/app.component.html (event-binding-to-component)"  region = "event-binding-to-component" >  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								When the `deleteRequest`  event fires, Angular calls the parent component's `deleteHero`  method,
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								passing the *hero-to-delete*  (emitted by `HeroDetail` ) in the `$event`  variable.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
										 
							
							
								当`deleteRequest` 事件触发时, `deleteHero` 方法,
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								在`$event` 变量中传入*要删除的英雄*(来自`HeroDetail` )。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								### Template statements have side effects
  
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								### 模板语句有副作用
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The `deleteHero`  method has a side effect: it deletes a hero.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Template statement side effects are not just OK, but expected.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								`deleteHero` 方法有副作用:它删除了一个英雄。 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								模板语句的副作用不仅没问题,反而正是所期望的。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Deleting the hero updates the model, perhaps triggering other changes
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								including queries and saves to a remote server.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								These changes percolate through the system and are ultimately displayed in this and other views.
							 
						 
					
						
							
								
									
										
										
										
											2017-07-30 17:40:53 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								删除这个英雄会更新模型,还可能触发其它修改,包括向远端服务器的查询和保存。
							 
						 
					
						
							
								
									
										
										
										
											2017-07-30 17:40:53 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								这些变更通过系统进行扩散,并最终显示到当前以及其它视图中。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-10 16:51:13 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< hr / >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								{@a  two-way}
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								## Two-way binding ( <span class="syntax">[(...)]</span> )
  
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								## 双向数据绑定 ( <span class="syntax">[(...)]</span> )
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								You often want to both display a data property and update that property when the user makes changes.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								我们经常需要显示数据属性,并在用户作出更改时更新该属性。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								On the element side that takes a combination of setting a specific element property
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								and listening for an element change event.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								在元素层面上,既要设置元素属性,又要监听元素事件变化。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Angular offers a special _two-way data binding_  syntax for this purpose, ** `[(x)]` **.
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								The `[(x)]`  syntax combines the brackets
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								of _property binding_ , `[x]` , with the parentheses of _event binding_ , `(x)` .
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
										 
							
							
								Angular 为此提供一种特殊的_双向数据绑定_语法: `[(x)]` **。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								`[(x)]` 语法结合了_属性绑定_的方括号`[x]` 和_事件绑定_的圆括号`(x)` 。 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-10 16:51:13 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< div  class = "callout is-important" >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								< header >  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  [( )] = banana in a box
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								< / header >  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< header >  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  [( )] = 盒子里的香蕉
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								< / header >  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Visualize a *banana in a box*  to remember that the parentheses go _inside_  the brackets.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								想象*盒子里的香蕉*来记住方括号套圆括号。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-10 16:51:13 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / div >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The `[(x)]`  syntax is easy to demonstrate when the element has a settable property called `x` 
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								and a corresponding event named `xChange` .
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Here's a `SizerComponent`  that fits the pattern.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								It has a `size`  value property and a companion `sizeChange`  event:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								当一个元素拥有可以设置的属性`x` 和对应的事件`xChange` 时,解释`[(x)]` 语法就容易多了。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								下面的`SizerComponent` 符合这个模式。它有`size` 属性和伴随的`sizeChange` 事件:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/sizer.component.ts"  title = "src/app/sizer.component.ts" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The initial `size`  is an input value from a property binding.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Clicking the buttons increases or decreases the `size` , within min/max values constraints,
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								and then raises (_emits_) the `sizeChange`  event with the adjusted size.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
										 
							
							
								`size` 的初始值是一个输入值,来自属性绑定。(译注:注意`size` 前面的`@Input` )  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								点击按钮,在最小/最大值范围限制内增加或者减少`size` 。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								然后用调整后的`size` 触发`sizeChange` 事件。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Here's an example in which the `AppComponent.fontSizePx`  is two-way bound to the `SizerComponent` :
							 
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
										 
							
							
								下面的例子中,`AppComponent.fontSize` 被双向绑定到`SizerComponent` : 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.html"  linenums = "false"  title = "src/app/app.component.html (two-way-1)"  region = "two-way-1" >  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The `AppComponent.fontSizePx`  establishes the initial `SizerComponent.size`  value.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Clicking the buttons updates the `AppComponent.fontSizePx`  via the two-way binding.
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								The revised `AppComponent.fontSizePx`  value flows through to the _style_  binding,
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								making the displayed text bigger or smaller.
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								`SizerComponent.size` 初始值是`AppComponent.fontSizePx` 。 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								点击按钮时,通过双向绑定更新`AppComponent.fontSizePx` 。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
										 
							
							
								被修改的`AppComponent.fontSizePx` 通过_样式_绑定, 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The two-way binding syntax is really just syntactic sugar for a _property_  binding and an _event_  binding.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Angular _desugars_  the `SizerComponent`  binding into this:
							 
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								双向绑定语法实际上是_属性_绑定和_事件绑定_的语法糖。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Angular将`SizerComponent` 的绑定分解成这样:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.html"  linenums = "false"  title = "src/app/app.component.html (two-way-2)"  region = "two-way-2" >  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The `$event`  variable contains the payload of the `SizerComponent.sizeChange`  event.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Angular assigns the `$event`  value to the `AppComponent.fontSizePx`  when the user clicks the buttons.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								`$event` 变量包含了`SizerComponent.sizeChange` 事件的荷载。 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
										 
							
							
								当用户点击按钮时, `$event` 赋值给`AppComponent.fontSizePx` 。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Clearly the two-way binding syntax is a great convenience compared to separate property and event bindings.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								显然,比起单独绑定属性和事件,双向数据绑定语法显得非常方便。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								It would be convenient to use two-way binding with HTML form elements like `<input>`  and `<select>` .
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								However, no native HTML element follows the `x`  value and `xChange`  event pattern.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								我们希望能在像`<input>` 和`<select>` 这样的 HTML 元素上使用双向数据绑定。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								可惜,原生 HTML 元素不遵循`x` 值和`xChange` 事件的模式。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 15:36:40 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								Fortunately, the Angular [_NgModel_ ](guide/template-syntax#ngModel ) directive is a bridge that enables two-way binding to form elements.
							 
						 
					
						
							
								
									
										
										
										
											2017-07-30 22:11:36 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
										 
							
							
								幸运的是, _NgModel_ ](guide/template-syntax#ngModel ) 指令为桥梁,允许在表单元素上使用双向数据绑定。
							 
						 
					
						
							
								
									
										
										
										
											2017-08-26 17:56:20 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-10 16:51:13 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< hr / >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								{@a  directives}
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								## Built-in directives
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								## 内置指令
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Earlier versions of Angular included over seventy built-in directives.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The community contributed many more, and countless private directives
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								have been created for internal applications.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								上一版本的 Angular 中包含了超过 70 个内置指令。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  社区贡献了更多,这还没算为内部应用而创建的无数私有指令。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								You don't need many of those directives in Angular.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								You can often achieve the same results with the more capable and expressive Angular binding system.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Why create a directive to handle a click when you can write a simple binding such as this?
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								在新版的 Angular 中不需要那么多指令。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  使用更强大、更富有表现力的 Angular 绑定系统,其实可以达到同样的效果。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  如果能用简单的绑定达到目的,为什么还要创建指令来处理点击事件呢?
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.html"  region = "event-binding-1"  title = "src/app/app.component.html"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								You still benefit from directives that simplify complex tasks.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Angular still ships with built-in directives; just not as many.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								You'll write your own directives, just not as many.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								我们仍然可以从简化复杂任务的指令中获益。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Angular 发布时仍然带有内置指令,只是没那么多了。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								我们仍会写自己的指令,只是没那么多了。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								This segment reviews some of the most frequently used built-in directives,
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 15:36:40 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								classified as either [_attribute_ directives ](guide/template-syntax#attribute-directives ) or [_structural_ directives ](guide/template-syntax#structural-directives ).
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								下面来看一下那些最常用的内置指令。它们可分为[*属性型*指令 ](guide/template-syntax#attribute-directives ) 或 [*结构型*指令 ](guide/template-syntax#structural-directives )。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-30 20:04:18 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-10 16:51:13 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< hr / >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								{@a  attribute-directives}
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								## Built-in _attribute_ directives
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								## 内置*属性型*指令
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Attribute directives listen to and modify the behavior of
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								other HTML elements, attributes, properties, and components.
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								They are usually applied to elements as if they were HTML attributes, hence the name.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
										 
							
							
								属性型指令会监听和修改其它HTML元素或组件的行为、元素属性( ) ( ) 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								它们通常会作为HTML属性的名称而应用在元素上。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 15:36:40 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								Many details are covered in the [_Attribute Directives_ ](guide/attribute-directives ) guide.
							 
						 
					
						
							
								
									
										
										
										
											2017-08-18 13:52:38 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								Many NgModules such as the [`RouterModule` ](guide/router "Routing and Navigation" )
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								and the [`FormsModule` ](guide/forms "Forms" ) define their own attribute directives.
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								This section is an introduction to the most commonly used attribute directives:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								更多的细节参见[_属性型指令_ ](guide/attribute-directives )一章。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
										 
							
							
								很多Angular模块, `RouterModule` ](guide/router "Routing and Navigation" )和[`FormsModule` ](guide/forms "Forms" )都定义了自己的属性型指令。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								本节将会介绍几个最常用的属性型指令:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 15:36:40 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								*  [`NgClass` ](guide/template-syntax#ngClass ) - add and remove a set of CSS classes 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  [`NgClass` ](guide/template-syntax#ngClass ) - 添加或移除一组CSS类
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 15:36:40 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								*  [`NgStyle` ](guide/template-syntax#ngStyle ) - add and remove a set of HTML styles 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  [`NgStyle` ](guide/template-syntax#ngStyle ) - 添加或移除一组CSS样式
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 15:36:40 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								*  [`NgModel` ](guide/template-syntax#ngModel ) - two-way data binding to an HTML form element 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  [`NgModel` ](guide/template-syntax#ngModel ) - 双向绑定到HTML表单元素
							 
						 
					
						
							
								
									
										
										
										
											2017-07-30 22:11:36 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-10 16:51:13 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< hr / >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								{@a  ngClass}
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								### NgClass
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-08-04 14:06:15 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								### NgClass 指令
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								You typically control how elements appear
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								by adding and removing CSS classes dynamically.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								You can bind to the `ngClass`  to add or remove several classes simultaneously.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								我们经常用动态添加或删除 CSS 类的方式来控制元素如何显示。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								通过绑定到`NgClass` ,可以同时添加或移除多个类。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 15:36:40 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								A [class binding ](guide/template-syntax#class-binding ) is a good way to add or remove a *single*  class.
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								[CSS 类绑定 ](guide/template-syntax#class-binding ) 是添加或删除*单个*类的最佳途径。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.html"  region = "class-binding-3a"  title = "src/app/app.component.html"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								To add or remove *many*  CSS classes at the same time, the `NgClass`  directive may be the better choice.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								当想要同时添加或移除*多个* CSS 类时,`NgClass` 指令可能是更好的选择。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-31 12:23:16 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								Try binding `ngClass`  to a key:value control object.
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								Each key of the object is a CSS class name; its value is `true`  if the class should be added,
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								`false`  if it should be removed. 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								试试把`ngClass` 绑定到一个 key:value 形式的控制对象。这个对象中的每个 key 都是一个 CSS 类名,如果它的 value 是`true` ,这个类就会被加上,否则就会被移除。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								Consider a `setCurrentClasses`  component method that sets a component property,
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								`currentClasses`  with an object that adds or removes three classes based on the 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								`true` /`false`  state of three other component properties: 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								组件方法`setCurrentClasses` 可以把组件的属性`currentClasses` 设置为一个对象,它将会根据三个其它组件的状态为`true` 或`false` 而添加或移除三个类。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.ts"  region = "setClasses"  title = "src/app/app.component.ts"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								Adding an `ngClass`  property binding to `currentClasses`  sets the element's classes accordingly:  
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
										 
							
							
								把`NgClass` 属性绑定到`currentClasses` , : 
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.html"  region = "NgClass-1"  title = "src/app/app.component.html"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-10 16:51:13 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< div  class = "l-sub-section" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								It's up to you to call `setCurrentClassess()` , both initially and when the dependent properties change.
							 
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								你既可以在初始化时调用`setCurrentClassess()` ,也可以在所依赖的属性变化时调用。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-10 16:51:13 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / div >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-10 16:51:13 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< hr / >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								{@a  ngStyle}
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								### NgStyle
  
						 
					
						
							
								
									
										
										
										
											2017-08-04 14:06:15 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								### NgStyle 指令
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								You can set inline styles dynamically, based on the state of the component.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								With `NgStyle`  you can set many inline styles simultaneously.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								我们可以根据组件的状态动态设置内联样式。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								`NgStyle` 绑定可以同时设置多个内联样式。 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 15:36:40 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								A [style binding ](guide/template-syntax#style-binding ) is an easy way to set a *single*  style value.
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								[样式绑定 ](guide/template-syntax#style-binding )是设置*单一*样式值的简单方式。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.html"  region = "NgStyle-1"  title = "src/app/app.component.html"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								To set *many*  inline styles at the same time, the `NgStyle`  directive may be the better choice.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								如果要同时设置*多个*内联样式,`NgStyle` 指令可能是更好的选择。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-31 12:23:16 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								Try binding `ngStyle`  to a key:value control object.
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Each key of the object is a style name; its value is whatever is appropriate for that style.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								`NgStyle` 需要绑定到一个 key:value 控制对象。 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  对象的每个 key 是样式名,它的 value 是能用于这个样式的任何值。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Consider a `setCurrentStyles`  component method that sets a component property, `currentStyles` 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								with an object that defines three styles, based on the state of three other component propertes:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								来看看组件的`setCurrentStyles` 方法,它会根据另外三个属性的状态把组件的`currentStyles` 属性设置为一个定义了三个样式的对象:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.ts"  region = "setStyles"  title = "src/app/app.component.ts"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Adding an `ngStyle`  property binding to `currentStyles`  sets the element's styles accordingly:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								把`NgStyle` 属性绑定到`currentStyles` ,以据此设置此元素的样式:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.html"  region = "NgStyle-2"  title = "src/app/app.component.html"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-10 16:51:13 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< div  class = "l-sub-section" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								It's up to you to call `setCurrentStyles()` , both initially and when the dependent properties change.
							 
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								你既可以在初始化时调用`setCurrentStyles()` ,也可以在所依赖的属性变化时调用。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-10 16:51:13 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / div >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-10 16:51:13 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< hr / >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								{@a  ngModel}
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								### NgModel - Two-way binding to form elements with <span class="syntax">[(ngModel)]</span>
  
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								### NgModel - 使用<span class="syntax">[(ngModel)]</span>双向绑定到表单元素
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								When developing data entry forms, you often both display a data property and
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								update that property when the user makes changes.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								当开发数据输入表单时,我们通常都要既显示数据属性又根据用户的更改去修改那个属性。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								Two-way data binding with the `NgModel`  directive makes that easy. Here's an example:
							 
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								使用`NgModel` 指令进行双向数据绑定可以简化这种工作。例子如下:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.html"  linenums = "false"  title = "src/app/app.component.html (NgModel-1)"  region = "NgModel-1" >  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-31 12:23:16 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								#### _FormsModule_ is required to use _ngModel_
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								#### 使用 `ngModel` 时需要 `FormsModule`
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-31 12:23:16 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								Before using the `ngModel`  directive in a two-way data binding,
							 
						 
					
						
							
								
									
										
										
										
											2017-07-11 18:05:20 -04:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								you must import the `FormsModule`  and add it to the NgModule's `imports`  list.
							 
						 
					
						
							
								
									
										
										
										
											2017-03-31 12:23:16 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								Learn more about the `FormsModule`  and `ngModel`  in the
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								[Forms ](guide/forms#ngModel ) guide.
							 
						 
					
						
							
								
									
										
										
										
											2017-03-31 12:23:16 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								在使用`ngModel` 指令进行双向数据绑定之前,我们必须导入`FormsModule` 并把它添加到Angular模块的`imports` 列表中。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								要了解`FormsModule` 和`ngModel` 的更多知识,参见[表单 ](guide/forms#ngModel )一章。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-31 12:23:16 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								Here's how to import the `FormsModule`  to make `[(ngModel)]`  available.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-08-04 07:39:15 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								导入`FormsModule` 并让`[(ngModel)]` 可用的代码如下:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.module.1.ts"  linenums = "false"  title = "src/app/app.module.ts (FormsModule import)"  >  
						 
					
						
							
								
									
										
										
										
											2017-03-31 12:23:16 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								#### Inside <span class="syntax">[(ngModel)]</span>
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								#### <span class="syntax">[(ngModel)]</span>内幕
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								Looking back at the `name`  binding, note that
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								you could have achieved the same result with separate bindings to
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								the `<input>`  element's  `value`  property and `input`  event.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								回头看看`name` 绑定,注意,你可以通过分别绑定到`<input>` 元素的`value` 属性和`input` 事件来达到同样的效果。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.html"  region = "without-NgModel"  title = "src/app/app.component.html"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								That's cumbersome. Who can remember which element property to set and which element event emits user changes?
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								How do you extract the currently displayed text from the input box so you can update the data property?
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Who wants to look that up each time?
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								那样显得很笨重,谁会记得该设置哪个元素属性以及当用户修改时触发哪个事件?
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								你该如何提取输入框中的文本并且更新数据属性?谁会希望每次都去查资料来确定这些?
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								That `ngModel`  directive hides these onerous details behind its own  `ngModel`  input and `ngModelChange`  output properties.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								`ngModel` 指令通过自己的输入属性`ngModel` 和输出属性`ngModelChange` 隐藏了那些细节。 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.html"  region = "NgModel-3"  title = "src/app/app.component.html"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-10 16:51:13 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< div  class = "l-sub-section" >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The `ngModel`  data property sets the element's value property and the `ngModelChange`  event property
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								listens for changes to the element's value.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								`ngModel` 输入属性会设置该元素的值,并通过`ngModelChange` 的输出属性来监听元素值的变化。 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								The details are specific to each kind of element and therefore the `NgModel`  directive only works for an element
							 
						 
					
						
							
								
									
										
										
										
											2017-04-30 22:10:32 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								supported by a [ControlValueAccessor ](api/forms/ControlValueAccessor )
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								that adapts an element to this protocol.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The `<input>`  box is one of those elements.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Angular provides *value accessors*  for all of the basic HTML form elements and the
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 15:36:40 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								[_Forms_ ](guide/forms ) guide shows how to bind to them.
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-30 12:32:56 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								各种元素都有很多特有的处理细节,因此`NgModel` 指令只支持实现了[ControlValueAccessor ](api/forms/ControlValueAccessor )的元素,
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								它们能让元素适配本协议。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								`<input>` 输入框正是其中之一。 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
										 
							
							
								Angular为所有的基础HTML表单都提供了*值访问器( ) , *表单* ](guide/forms )一章展示了如何绑定它们。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								You can't apply `[(ngModel)]`  to a non-form native element or a third-party custom component
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								until you write a suitable *value accessor* ,
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								a technique that is beyond the scope of this guide.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								我们不能把`[(ngModel)]` 用到非表单类的原生元素或第三方自定义组件上,除非写一个合适的*值访问器*,这种技巧超出了本章的范围。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								You don't need a _value accessor_  for an Angular component that you write because you
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								can name the value and event properties
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 15:36:40 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								to suit Angular's basic [two-way binding syntax ](guide/template-syntax#two-way ) and skip `NgModel`  altogether.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The [`sizer` shown above ](guide/template-syntax#two-way ) is an example of this technique.
							 
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
										 
							
							
								我们自己写的Angular组件不需要*值访问器*, 双向绑定语法 ](guide/template-syntax#two-way ),而不使用`NgModel` 。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								[前面看过的`sizer` ](guide/template-syntax#two-way )就是使用这种技巧的例子。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-10 16:51:13 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / div >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Separate `ngModel`  bindings is an improvement over binding to the element's native properties. You can do better.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								使用独立的`ngModel` 绑定优于绑定到该元素的原生属性,那样我们可以做得更好。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								You shouldn't have to mention the data property twice. Angular should be able to capture
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								the component's data property and set it
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								with a single declaration, which it can with the `[(ngModel)]`  syntax:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
										 
							
							
								我们不用被迫两次引用这个数据属性, , , `[(ngModel)]` 语法了。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.html"  region = "NgModel-1"  title = "src/app/app.component.html"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Is `[(ngModel)]`  all you need? Is there ever a reason to fall back to its expanded form?
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								`[(ngModel)]` 就是你需要的一切吗?有没有什么理由回退到它的展开形式? 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The `[(ngModel)]`  syntax can only _set_  a data-bound property.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								If you need to do something more or something different, you can write the expanded form.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								`[(ngModel)]` 语法只能*设置*数据绑定属性。 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								如果要做更多或者做点不一样的事,也可以写它的展开形式。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The following contrived example forces the input value to uppercase:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								下面这个生造的例子强制输入框的内容变成大写:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.html"  region = "NgModel-4"  title = "src/app/app.component.html"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Here are all variations in action, including the uppercase version:
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-30 20:04:18 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-08-04 09:27:48 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								这里是所有这些变体的动画,包括这个大写转换的版本:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								< figure  >  
						 
					
						
							
								
									
										
										
										
											2017-05-09 23:53:32 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								  < img  src = 'generated/images/guide/template-syntax/ng-model-anim.gif'  alt = "NgModel variations" > 
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								< / figure >  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-10 16:51:13 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< hr / >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								{@a  structural-directives}
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								## Built-in _structural_ directives
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								## 内置*结构型*指令
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Structural directives are responsible for HTML layout.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								They shape or reshape the DOM's _structure_ , typically by adding, removing, and manipulating
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								the host elements to which they are attached.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								结构型指令的职责是HTML布局。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								它们塑造或重塑DOM的*结构*,这通常是通过添加、移除和操纵它们所附加到的宿主元素来实现的。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								The deep details of structural directives are covered in the
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 15:36:40 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								[_Structural Directives_ ](guide/structural-directives ) guide
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								where you'll learn:
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								关于结构型指令的详情参见[*结构型指令* ](guide/structural-directives )一章,在那里我们将学到:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								*  why you 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								[_prefix the directive name with an asterisk_ (\*) ](guide/structural-directives#asterisk "The * in *ngIf" ).
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  为什么要[给结构型指令的名字加上(\*)前缀? ](guide/structural-directives#asterisk "The * in *ngIf" )
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								*  to use [`<ng-container>` ](guide/structural-directives#ngcontainer "<ng-container>" ) 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								to group elements when there is no suitable host element for the directive.
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  当没有合适的宿主元素防止指令时,可用`<ng-container>` ](structural-directives.html#ngcontainer  "< ng-container > 对元素进行分组。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								*  how to write your own structural directive. 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  如何写自己的结构型指令。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								*  that you can only apply [one structural directive ](guide/structural-directives#one-per-element "one per host element" ) to an element. 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								  我们只能往一个元素上应用[一个结构型指令 ](guide/structural-directives#one-per-element "one per host element" )。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								_This_ section is an introduction to the common structural directives:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								*本节*是对常见结构型指令的简介:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 15:36:40 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								*  [`NgIf` ](guide/template-syntax#ngIf ) - conditionally add or remove an element from the DOM 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  [`NgIf` ](guide/template-syntax#ngIf ) - 根据条件把一个元素添加到DOM中或从DOM移除
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 15:36:40 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								*  [`NgSwitch` ](guide/template-syntax#ngSwitch ) - a set of directives that switch among alternative views 
						 
					
						
							
								
									
										
										
										
											2017-08-17 11:40:46 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								*  [NgForOf ](guide/template-syntax#ngFor ) - repeat a template for each item in a list 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								  [`NgSwitch` ](guide/template-syntax#ngSwitch ) - 一组指令,用于切换一组视图
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-10-01 11:40:31 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								*  [NgForOf ](guide/template-syntax#ngFor ) - repeat a template for each item in a list 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  [NgForOf ](guide/template-syntax#ngFor ) - 对列表中的每个条目重复套用同一个模板
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-30 20:04:18 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-10 16:51:13 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< hr / >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								{@a  ngIf}
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								### NgIf
  
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-08-04 14:06:15 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								### NgIf 指令
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								You can add or remove an element from the DOM by applying an `NgIf`  directive to
							 
						 
					
						
							
								
									
										
										
										
											2017-07-06 09:43:21 -07:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								that element (called the _host element_ ).
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Bind the directive to a condition expression like `isActive`  in this example.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
										 
							
							
								通过把`NgIf` 指令应用到元素上(称为*宿主元素*) , 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								在下面的例子中,该指令绑定到了类似于`isActive` 这样的条件表达式。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.html"  region = "NgIf-1"  title = "src/app/app.component.html"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-10 16:51:13 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< div  class = "alert is-critical" >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Don't forget the asterisk (`*` ) in front of `ngIf` .
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								别忘了`ngIf` 前面的星号(`*` )。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-10 16:51:13 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / div >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-31 12:23:16 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								When the `isActive`  expression returns a truthy value, `NgIf`  adds the `HeroDetailComponent`  to the DOM.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								When the expression is falsy, `NgIf`  removes the `HeroDetailComponent` 
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								from the DOM, destroying that component and all of its sub-components.
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
										 
							
							
								当`isActive` 表达式返回真值时,`NgIf` 把`HeroDetailComponent` 添加到DOM中; , `NgIf` 会从DOM中移除`HeroDetailComponent` ,并销毁该组件及其所有子组件。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								#### Show/hide is not the same thing
  
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								#### 这和显示/隐藏不是一回事
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								You can control the visibility of an element with a
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 15:36:40 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								[class ](guide/template-syntax#class-binding ) or [style ](guide/template-syntax#style-binding ) binding:
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								我们也可以通过[类绑定 ](guide/template-syntax#class-binding )或[样式绑定 ](guide/template-syntax#style-binding )来显示或隐藏一个元素。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.html"  region = "NgIf-3"  title = "src/app/app.component.html"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Hiding an element is quite different from removing an element with `NgIf` .
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								但隐藏子树和用`NgIf` 排除子树是截然不同的。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								When you hide an element, that element and all of its descendents remain in the DOM.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								All components for those elements stay in memory and
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Angular may continue to check for changes.
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								You could be holding onto considerable computing resources and degrading performance,
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								for something the user can't see.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								当隐藏子树时,它仍然留在 DOM 中。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								子树中的组件及其状态仍然保留着。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
										 
							
							
								即使对于不可见属性, 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								子树可能占用相当可观的内存和运算资源。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								When `NgIf`  is `false` , Angular removes the element and its descendents from the DOM.
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								It destroys their components, potentially freeing up substantial resources,
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								resulting in a more responsive user experience.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
										 
							
							
								当`NgIf` 为`false` 时, 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								它销毁了子树中的组件及其状态,也潜在释放了可观的资源,最终让用户体验到更好的性能。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The show/hide technique is fine for a few elements with few children.
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								You should be wary when hiding large component trees; `NgIf`  may be the safer choice.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								显示/隐藏的技术对于只有少量子元素的元素是很好用的,但要当心别试图隐藏大型组件树。相比之下,`NgIf` 则是个更安全的选择。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								#### Guard against null
  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								#### 防范空指针错误
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								The `ngIf`  directive is often used to guard against null.
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Show/hide is useless as a guard.
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								Angular will throw an error if a nested expression tries to access a property of `null` .
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								`ngIf` 指令通常会用来防范空指针错误。 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
										 
							
							
								而显示/隐藏的方式是无法防范的, , 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								Here we see `NgIf`  guarding two `<div>` s.
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The `currentHero`  name will appear only when there is a `currentHero` .
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The `nullHero`  will never be displayed.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								这里我们用`NgIf` 来保护了两个`<div>` 防范空指针错误。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								`currentHero` 的名字只有当存在`currentHero` 时才会显示出来。 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								而`nullHero` 永远不会显示。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.html"  region = "NgIf-2"  title = "src/app/app.component.html"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-10 16:51:13 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< div  class = "l-sub-section" >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								See also the
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 15:36:40 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								[_safe navigation operator_ ](guide/template-syntax#safe-navigation-operator "Safe naviation operator (?. )")
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								described below.
							 
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								参见稍后的[_安全导航操作符_ ](guide/template-syntax#safe-navigation-operator "Safe naviation operator (?. )")部分。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-10 16:51:13 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / div >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-10 16:51:13 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< hr / >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								{@a  ngFor}
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-08-17 11:40:46 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								### NgForOf
  
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-08-04 14:06:15 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								### NgFor 指令
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-08-17 11:40:46 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								`NgForOf`  is a _repeater_  directive —  a way to present a list of items. 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								You define a block of HTML that defines how a single item should be displayed.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								You tell Angular to use that block as a template for rendering each item in the list.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								`NgFor` 是一个_重复器_指令 —— 自定义数据显示的一种方式。 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								我们的目标是展示一个由多个条目组成的列表。首先定义了一个 HTML 块,它规定了单个条目应该如何显示。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								再告诉 Angular 把这个块当做模板,渲染列表中的每个条目。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-08-17 11:40:46 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								Here is an example of `NgForOf`  applied to a simple `<div>` :
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								下例中,`NgFor` 应用在一个简单的`<div>` 上:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.html"  region = "NgFor-1"  title = "src/app/app.component.html"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-08-17 11:40:46 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								You can also apply an `NgForOf`  to a component element, as in this example:
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								也可以把`NgFor` 应用在一个组件元素上,就下例这样:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.html"  region = "NgFor-2"  title = "src/app/app.component.html"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-10 16:51:13 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< div  class = "alert is-critical" >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Don't forget the asterisk (`*` ) in front of `ngFor` .
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								不要忘了`ngFor` 前面的星号 (`*` )。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-10 16:51:13 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / div >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The text assigned to `*ngFor`  is the instruction that guides the repeater process.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								赋值给`*ngFor` 的文本是用于指导重复器如何工作的指令。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								{@a  microsyntax}
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								#### *ngFor microsyntax
  
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								#### NgFor 微语法
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 15:36:40 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								The string assigned to `*ngFor`  is not a [template expression ](guide/template-syntax#template-expressions ).
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								It's a *microsyntax*  —  a little language of its own that Angular interprets.
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The string `"let hero of heroes"`  means:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								赋值给`*ngFor` 的字符串不是[模板表达式 ](guide/template-syntax#template-expressions )。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								它是一个*微语法* —— 由 Angular 自己解释的小型语言。在这个例子中,字符串`"let hero of heroes"` 的含义是:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-31 12:23:16 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								>  *Take each hero in the `heroes` array, store it in the local `hero` looping variable, and
  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								make it available to the templated HTML for each iteration.*
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								>  *取出`heroes`数组中的每个英雄,把它存入局部变量`hero`中,并在每次迭代时对模板 HTML 可用*
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-12 21:53:18 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								Angular translates this instruction into a `<ng-template>`  around the host element,
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								then uses this template repeatedly to create a new set of elements and bindings for each `hero` 
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								in the list.
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								Angular 把这个指令翻译成了一个`<ng-template>` 包裹的宿主元素,然后使用这个模板重复创建出一组新元素,并且绑定到列表中的每一个`hero` 。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								Learn about the _microsyntax_  in the [_Structural Directives_ ](guide/structural-directives#microsyntax ) guide.
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								要了解*微语法*的更多知识,参见[_结构型指令_ ](guide/structural-directives#microsyntax )一章。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								{@a  template-input-variable}
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								{@a  template-input-variables}
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								### Template input variables
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								### 模板输入变量
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The `let`  keyword before `hero`  creates a _template input variable_  called `hero` .
							 
						 
					
						
							
								
									
										
										
										
											2017-08-17 11:40:46 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								The `NgForOf`  directive iterates over the `heroes`  array returned by the parent component's `heroes`  property
							 
						 
					
						
							
								
									
										
										
										
											2017-03-31 12:23:16 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								and sets `hero`  to the current item from the array during each iteration.
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								`hero` 前的`let` 关键字创建了一个名叫`hero` 的*模板输入变量*。 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								`ngFor` 指令在由父组件的`heroes` 属性返回的`heroes` 数组上迭代,每次迭代都从数组中把当前元素赋值给`hero` 变量。 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-08-17 11:40:46 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								You reference the `hero`  input variable within the `NgForOf`  host element
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								(and within its descendents) to access the hero's properties.
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Here it is referenced first in an interpolation
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								and then passed in a binding to the `hero`  property of the `<hero-detail>`  component.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								我们可以在`ngFor` 的宿主元素(及其子元素)中引用模板输入变量`hero` ,从而访问该英雄的属性。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								这里它首先在一个插值表达式中被引用到,然后通过一个绑定把它传给了`<hero-detail>` 组件的`hero` 属性。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.html"  region = "NgFor-1-2"  title = "src/app/app.component.html"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								Learn more about _template input variables_  in the
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								[_Structural Directives_ ](guide/structural-directives#template-input-variable ) guide.
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								要了解更多*模板输入变量*的知识,参见[*结构型指令* ](guide/structural-directives#template-input-variable )一章。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								#### *ngFor with _index_
  
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								#### 带索引的`*ngFor`
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-08-17 11:40:46 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								The `index`  property of the `NgForOf`  directive context returns the zero-based index of the item in each iteration.
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								You can capture the `index`  in a template input variable and use it in the template.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								`NgFor` 指令上下文中的`index` 属性返回一个从零开始的索引,表示当前条目在迭代中的顺序。 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								我们可以通过模板输入变量捕获这个`index` 值,并把它用在模板中。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The next example captures the `index`  in a variable named `i`  and displays it with the hero name like this.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								下面这个例子把`index` 捕获到了`i` 变量中,并且把它显示在英雄名字的前面。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.html"  region = "NgFor-3"  title = "src/app/app.component.html"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-10 16:51:13 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< div  class = "l-sub-section" >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-09-27 18:25:41 -04:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								`NgFor`  is implemented by the `NgForOf`  directive. Read more about the other `NgForOf`  context values such as `last` , `even` , 
						 
					
						
							
								
									
										
										
										
											2017-08-17 11:40:46 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								and `odd`  in the [NgForOf API reference ](api/common/NgForOf ).
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-10-01 11:40:31 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								要学习更多的*类似 index* 的值,例如`last` 、`even` 和`odd` ,请参阅 [NgFor API 参考 ](api/common/NgForOf )。
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-10 16:51:13 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / div >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								{@a  trackBy}
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								#### *ngFor with _trackBy_
  
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								#### 带`trackBy`的`*ngFor`
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-08-17 11:40:46 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								The `NgForOf`  directive may perform poorly, especially with large lists.
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								A small change to one item, an item removed, or an item added can trigger a cascade of DOM manipulations.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								`ngFor` 指令有时候会性能较差,特别是在大型列表中。 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								对一个条目的一丁点改动、移除或添加,都会导致级联的 DOM 操作。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								For example, re-querying the server could reset the list with all new hero objects.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								例如,我们可以通过重新从服务器查询来刷新英雄列表。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  刷新后的列表可能包含很多(如果不是全部的话)以前显示过的英雄。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Most, if not all, are previously displayed heroes.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								*You* know this because the `id`  of each hero hasn't changed.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								But Angular sees only a fresh list of new object references.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								It has no choice but to tear down the old DOM elements and insert all new DOM elements.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-09-19 18:25:56 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								他们中的绝大多数(如果不是所有的话)都是以前显示过的英雄。*我们*知道这一点,是因为每个英雄的`id` 没有变化。
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								  但在 Angular 看来,它只是一个由新的对象引用构成的新列表,
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  它没有选择,只能清理旧列表、舍弃那些 DOM 元素,并且用新的 DOM 元素来重建一个新列表。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Angular can avoid this churn with `trackBy` .
							 
						 
					
						
							
								
									
										
										
										
											2017-08-17 11:40:46 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								Add a method to the component that returns the value `NgForOf`  _should_  track.
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								In this case, that value is the hero's `id` .
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
										 
							
							
								如果给它指定一个`trackBy` , 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  我们往组件中添加一个方法,它会返回`NgFor` *应该*追踪的值。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  在这里,这个值就是英雄的`id` 。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.ts"  region = "trackByHeroes"  title = "src/app/app.component.ts"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								In the microsyntax expression, set `trackBy`  to this method.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								在微语法中,把`trackBy` 设置为该方法。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.html"  region = "trackBy"  title = "src/app/app.component.html"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Here is an illustration of the _trackBy_  effect.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								"Reset heroes" creates new heroes with the same `hero.id` s.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								"Change ids" creates new heroes with new `hero.id` s.
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								这里展示了`trackBy` 的效果。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								"Reset heroes"会创建一个具有相同`hero.id` 的新英雄。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								"Change ids"则会创建一个具有新`hero.id` 的新英雄。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								*  With no `trackBy` , both buttons trigger complete DOM element replacement. 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
										 
							
							
								  如果没有`trackBy` , 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								*  With `trackBy` , only changing the `id`  triggers element replacement. 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-30 20:04:18 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-08-04 09:27:48 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								有了`trackBy` ,则只有修改了`id` 的按钮才会触发元素替换。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								< figure  >  
						 
					
						
							
								
									
										
										
										
											2017-05-09 23:53:32 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								  < img  src = "generated/images/guide/template-syntax/ng-for-track-by-anim.gif"  alt = "trackBy" > 
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								< / figure >  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-30 00:03:22 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< a  href = " #top -of-page" > 回到顶部</ a >  
						 
					
						
							
								
									
										
										
										
											2017-03-30 20:04:18 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-10 16:51:13 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< hr / >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								{@a  ngSwitch}
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								### The _NgSwitch_ directives
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								### `NgSwitch`指令
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								*NgSwitch* is like the JavaScript `switch`  statement.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								It can display _one_  element from among several possible elements, based on a _switch condition_ .
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Angular puts only the *selected*  element into the DOM.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								`NgSwitch` 指令类似于JavaScript的`switch` 语句。 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								它可以从多个可能的元素中根据*switch条件*来显示某一个。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Angular只会把*选中的*元素放进DOM中。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								*NgSwitch* is actually a set of three, cooperating directives:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								`NgSwitch` , `NgSwitchCase` , and `NgSwitchDefault`  as seen in this example. 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								`NgSwitch` 实际上包括三个相互协作的指令:`NgSwitch` 、`NgSwitchCase`  和 `NgSwitchDefault` ,例子如下: 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.html"  region = "NgSwitch"  title = "src/app/app.component.html"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-05-09 23:53:32 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< figure >  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  < img  src = "generated/images/guide/template-syntax/switch-anim.gif"  alt = "trackBy" > 
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								< / figure >  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								`NgSwitch`  is the controller directive. Bind it to an expression that returns the *switch value* . 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The `emotion`  value in this example is a string, but the switch value can be of any type.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								`NgSwitch` 是主控指令,要把它绑定到一个返回*候选值*的表达式。 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								本例子中的`emotion` 是个字符串,但实际上这个候选值可以是任意类型。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								**Bind to `[ngSwitch]` **. You'll get an error if you try to set `*ngSwitch`  because
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								`NgSwitch`  is an *attribute*  directive, not a *structural*  directive. 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								It changes the behavior of its companion directives.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								It doesn't touch the DOM directly.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								**绑定到`[ngSwitch]` **。如果试图用`*ngSwitch` 的形式使用它就会报错,这是因为`NgSwitch` 是一个*属性型*指令,而不是*结构型指令*。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
										 
							
							
								它要修改的是所在元素的行为, 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								**Bind to `*ngSwitchCase`  and `*ngSwitchDefault` **.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The `NgSwitchCase`  and `NgSwitchDefault`  directives are _structural_  directives
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								because they add or remove elements from the DOM.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								**绑定到`*ngSwitchCase` 和`*ngSwitchDefault` **
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
										 
							
							
								`NgSwitchCase`  和 `NgSwitchDefault`  指令都是*结构型指令*,  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								*  `NgSwitchCase`  adds its element to the DOM when its bound value equals the switch value. 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
										 
							
							
								  `NgSwitchCase` 会在它绑定到的值等于候选值时, 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								*  `NgSwitchDefault`  adds its element to the DOM when there is no selected `NgSwitchCase` . 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								  `NgSwitchDefault` 会在没有任何一个`NgSwitchCase` 被选中时把它所在的元素加入DOM中。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The switch directives are particularly useful for adding and removing *component elements* .
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								This example switches among four "emotional hero" components defined in the `hero-switch.components.ts`  file.
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 15:36:40 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								Each component has a `hero`  [input property ](guide/template-syntax#inputs-outputs "Input property" )
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								which is bound to the `currentHero`  of the parent component.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								这组指令在要添加或移除*组件元素*时会非常有用。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								这个例子会在`hero-switch.components.ts` 中定义的四个“感人英雄”组件之间选择。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								每个组件都有一个[输入属性 ](guide/template-syntax#inputs-outputs "Input property" )`hero` ,它绑定到父组件的`currentHero` 上。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Switch directives work as well with native elements and web components too.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								For example, you could replace the `<confused-hero>`  switch case with the following.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								这组指令在原生元素和< a  href = "https://developer.mozilla.org/en-US/docs/Web/Web_Components"  target = "_blank"  title = "MDN: Web Components" > Web Component< / a > 上都可以正常工作。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								比如,你可以把`<confused-hero>` 分支改成这样:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.html"  region = "NgSwitch-div"  title = "src/app/app.component.html"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-10 16:51:13 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< hr / >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								{@a  template-reference-variable}
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								{@a  ref-vars}
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								{@a  ref-var}
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								## Template reference variables ( <span class="syntax">#var</span> )
  
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								## 模板引用变量 ( <span class="syntax">#var</span> )
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								A **template reference variable**  is often a reference to a DOM element within a template.
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								It can also be a reference to an Angular component or directive or a
							 
						 
					
						
							
								
									
										
										
										
											2017-04-24 20:23:45 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< a  href = "https://developer.mozilla.org/en-US/docs/Web/Web_Components"  title = "MDN: Web Components" > web component< / a > . 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
										 
							
							
								**模板引用变量**通常用来引用模板中的某个DOM元素, < a  href = "https://developer.mozilla.org/en-US/docs/Web/Web_Components"  target = "_blank"  title = "MDN: Web Components" > Web Component< / a > 。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Use the hash symbol (#) to declare a reference variable.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The `#phone`  declares a `phone`  variable on an `<input>`  element.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								使用井号 (#) 来声明引用变量。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								`#phone` 的意思就是声明一个名叫`phone` 的变量来引用`<input>` 元素。 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.html"  region = "ref-var"  title = "src/app/app.component.html"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								You can refer to a template reference variable _anywhere_  in the template.
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								The `phone`  variable declared on this `<input>`  is
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								consumed in a `<button>`  on the other side of the template
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								我们可以在模板中的任何地方引用模板引用变量。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								比如声明在`<input>` 上的`phone` 变量就是在模板另一侧的`<button>` 上使用的。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.html"  region = "ref-phone"  title = "src/app/app.component.html"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-05-08 20:47:34 -07:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< h3  class = "no-toc" > How a reference variable gets its value< / h3 >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								### 模板引用变量怎么得到它的值?
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								In most cases, Angular sets the reference variable's value to the element on which it was declared.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								In the previous example, `phone`  refers to the _phone number_  `<input>`  box.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The phone button click handler passes the _input_  value to the component's `callPhone`  method.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								But a directive can change that behavior and set the value to something else, such as itself.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The `NgForm`  directive does that.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
										 
							
							
								大多数情况下, 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								在上一个例子中,`phone` 引用的是表示*电话号码*的`<input>` 框。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								"拨号"按钮的点击事件处理器把这个*input*值传给了组件的`callPhone` 方法。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								不过,指令也可以修改这种行为,让这个值引用到别处,比如它自身。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								`NgForm` 指令就是这么做的。 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 15:36:40 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								The following is a *simplified*  version of the form example in the [Forms ](guide/forms ) guide.
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								下面是[表单 ](guide/forms )一章中表单范例的*简化版*。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/hero-form.component.html"  title = "src/app/hero-form.component.html"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								A template reference variable, `heroForm` , appears three times in this example, separated
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								by a large amount of HTML.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								What is the value of `heroForm` ?
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
										 
							
							
								模板引用变量`heroForm` 在这个例子中出现了三次, 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								`heroForm` 的值是什么? 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								If Angular hadn't taken it over when you imported the `FormsModule` ,
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								it would be the [HTMLFormElement ](https://developer.mozilla.org/en-US/docs/Web/API/HTMLFormElement ).
							 
						 
					
						
							
								
									
										
										
										
											2017-04-30 22:10:32 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								The `heroForm`  is actually a reference to an Angular [NgForm ](api/forms/NgForm "API: NgForm" )
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								directive with the ability to track the value and validity of every control in the form.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
										 
							
							
								如果你没有导入过`FormsModule` , , HTMLFormElement ](https://developer.mozilla.org/en-US/docs/Web/API/HTMLFormElement )实例。
							 
						 
					
						
							
								
									
										
										
										
											2017-07-30 12:32:56 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								这里的`heroForm` 实际上是一个Angular [NgForm ](api/forms/NgForm "API: NgForm" ) 指令的引用,
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								因此具备了跟踪表单中的每个控件的值和有效性的能力。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The native `<form>`  element doesn't have a `form`  property.
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								But the `NgForm`  directive does, which explains how you can disable the submit button
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								if the `heroForm.form.valid`  is invalid and pass the entire form control tree
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								to the parent component's `onSubmit`  method.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								原生的`<form>` 元素没有`form` 属性,但`NgForm` 指令有。这就解释了为何当`heroForm.form.valid` 是无效时我们可以禁用提交按钮,
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								并能把整个表单控件树传给父组件的`onSubmit` 方法。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-05-08 20:47:34 -07:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< h3  class = "no-toc" > Template reference variable warning notes< / h3 >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-30 00:03:22 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< h3  class = "no-toc" > 关于模板引用变量的提醒< / h3 >  
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								A template _reference_  variable (`#phone` ) is _not_  the same as a template _input_  variable (`let phone` )
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 15:36:40 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								such as you might see in an [`*ngFor` ](guide/template-syntax#template-input-variable ).
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								Learn the difference in the [_Structural Directives_ ](guide/structural-directives#template-input-variable ) guide.
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								模板*引用*变量 (`#phone` ) 和[`*ngFor` ](guide/template-syntax#template-input-variable )部分看到过的模板*输入*变量 (`let phone` ) 是不同的。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								要了解详情,参见[结构型指令 ](guide/structural-directives#template-input-variable )一章。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The scope of a reference variable is the _entire template_ .
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Do not define the same variable name more than once in the same template.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The runtime value will be unpredictable.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								模板引用变量的作用范围是*整个模板*。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								不要在同一个模板中多次定义同一个变量名,否则它在运行期间的值是无法确定的。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								You can use the `ref-`  prefix alternative to `#` .
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								This example declares the `fax`  variable as `ref-fax`  instead of `#fax` .
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								我们也可以用`ref-` 前缀代替`#` 。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								下面的例子中就用把`fax` 变量声明成了`ref-fax` 而不是`#fax` 。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.html"  region = "ref-fax"  title = "src/app/app.component.html"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-10 16:51:13 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< hr / >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								{@a  inputs-outputs}
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								## Input and output properties ( <span class="syntax">@Input</span> and <span class="syntax">@Output</span> )
  
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								## 输入输出属性 ( <span class="syntax">@Input</span> 和 <span class="syntax">@Output</span> )
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								So far, you've focused mainly on binding to component members within template expressions and statements
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								that appear on the *right side of the binding declaration* .
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								A member in that position is a data binding **source** .
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								迄今为止,我们主要聚焦在*绑定声明的右侧*,学习如何在模板表达式和模板语句中绑定到组件成员。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								当成员出现在这个位置上,则称之为数据绑定的**源**。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								This section concentrates on binding to **targets** , which are directive
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								properties on the *left side of the binding declaration* .
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								These directive properties must be declared as **inputs**  or **outputs** .
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								本节则专注于绑定到的**目标**,它位于*绑定声明中的左侧*。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								这些指令的属性必须被声明成**输入**或**输出**。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-10 16:51:13 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< div  class = "alert is-important" >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Remember: All **components**  are **directives** .
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								记住:所有**组件**皆为**指令**。
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-10 16:51:13 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / div >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-10 16:51:13 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< div  class = "l-sub-section" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								Note the important distinction between a data binding **target**  and a data binding **source** .
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								我们要重点突出下绑定**目标**和绑定**源**的区别。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The *target*  of a binding is to the *left*  of the `=` .
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The *source*  is on the *right*  of the `=` .
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								绑定的*目标*是在`=` *左侧*的部分,
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								*源*则是在`=` *右侧*的部分。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The *target*  of a binding is the property or event inside the binding punctuation: `[]` , `()`  or `[()]` .
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The *source*  is either inside quotes (`" "` ) or within an interpolation (`{{}}` ).
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								绑定的*目标*是绑定符:`[]` 、`()` 或`[()]` 中的属性或事件名,
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								*源*则是引号 (`" "` ) 中的部分或插值符号 (`{{}}` ) 中的部分。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Every member of a **source**  directive is automatically available for binding.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								You don't have to do anything special to access a directive member in a template expression or statement.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								**源**指令中的每个成员都会自动在绑定中可用。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								    不需要特别做什么,就能在模板表达式或语句中访问指令的成员。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								You have *limited*  access to members of a **target**  directive.
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								You can only bind to properties that are explicitly identified as *inputs*  and *outputs* .
							 
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								访问**目标**指令中的成员则*受到限制*。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								    只能绑定到那些显式标记为*输入*或*输出*的属性。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-10 16:51:13 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / div >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								In the following snippet, `iconUrl`  and `onSave`  are data-bound members of the `AppComponent` 
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								and are referenced within quoted syntax to the _right_  of the equals  (`=` ).
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								在下面的例子中,`iconUrl` 和`onSave` 是组件的成员,它们在`=` 右侧引号语法中被引用了。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.html"  region = "io-1"  title = "src/app/app.component.html"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								They are *neither inputs nor outputs*  of the component. They are **sources**  for their bindings.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The targets are the native `<img>`  and `<button>`  elements.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								它们既不是组件的*输入*也不是*输出*。它们是绑定的数据源。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								Now look at a another snippet in which the `HeroDetailComponent` 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								is the **target**  of a binding on the _left_  of the equals  (`=` ).
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
										 
							
							
								现在,看看`HeroDetailComponent` 中的另一个片段,等号(`=` ) 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.html"  region = "io-2"  title = "src/app/app.component.html"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Both `HeroDetailComponent.hero`  and `HeroDetailComponent.deleteRequest`  are on the **left side**  of binding declarations.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								`HeroDetailComponent.hero`  is inside brackets; it is the target of a property binding. 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								`HeroDetailComponent.deleteRequest`  is inside parentheses; it is the target of an event binding. 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								`HeroDetailComponent.hero` 和`HeroDetailComponent.deleteRequest` 都在绑定声明的**左侧**。 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								`HeroDetailComponent.hero` 在方括号中,它是属性绑定的目标。 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								`HeroDetailComponent.deleteRequest` 在圆括号中,它是事件绑定的目标。 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								### Declaring input and output properties
  
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								### 声明输入和输出属性
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Target properties must be explicitly marked as inputs or outputs.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								目标属性必须被显式的标记为输入或输出。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								In the `HeroDetailComponent` , such properties are marked as input or output properties using decorators.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								在`HeroDetailComponent` 内部,这些属性被装饰器标记成了输入和输出属性。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/hero-detail.component.ts"  region = "input-output-1"  title = "src/app/hero-detail.component.ts"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-10 16:51:13 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< div  class = "l-sub-section" >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-31 12:23:16 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								Alternatively, you can identify members in the `inputs`  and `outputs`  arrays
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								of the directive metadata, as in this example:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								另外,还可以在指令元数据的`inputs` 或`outputs` 数组中标记出这些成员。比如这个例子:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/hero-detail.component.ts"  region = "input-output-2"  title = "src/app/hero-detail.component.ts"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-31 12:23:16 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								You can specify an input/output property either with a decorator or in a metadata array.
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								Don't do both!
							 
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								既可以通过装饰器,也可以通过元数据数组来指定输入/输出属性。但别同时用!
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-10 16:51:13 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / div >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								### Input or output?
  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								### 输入还是输出?
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								*Input* properties usually receive data values.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								*Output* properties expose event producers, such as `EventEmitter`  objects.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								*输入*属性通常接收数据值。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								*输出*属性暴露事件生产者,如`EventEmitter` 对象。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The terms _input_  and _output_  reflect the perspective of the target directive.
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-08-04 09:27:48 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								_输入_和_输出_这两个词是从目标指令的角度来说的。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								< figure  >  
						 
					
						
							
								
									
										
										
										
											2017-05-09 23:53:32 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								  < img  src = "generated/images/guide/template-syntax/input-output.png"  alt = "Inputs and outputs" > 
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								< / figure >  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								`HeroDetailComponent.hero`  is an **input**  property from the perspective of `HeroDetailComponent`  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								because data flows *into*  that property from a template binding expression.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								从`HeroDetailComponent` 角度来看,`HeroDetailComponent.hero` 是个**输入**属性,
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								因为数据流从模板绑定表达式流*入*那个属性。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								`HeroDetailComponent.deleteRequest`  is an **output**  property from the perspective of `HeroDetailComponent`  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								because events stream *out*  of that property and toward the handler in a template binding statement.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								从`HeroDetailComponent` 角度来看,`HeroDetailComponent.deleteRequest` 是个**输出**属性,
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								因为事件从那个属性流*出*,流向模板绑定语句中的处理器。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-30 20:04:18 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								< h3  id = 'aliasing-io' >  
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  < p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								     Aliasing input/output properties
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  < / p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  < p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								     给输入/输出属性起别名
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  < / p > 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								< / h3 >  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Sometimes the public name of an input/output property should be different from the internal name.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								有时需要让输入/输出属性的公开名字不同于内部名字。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 15:36:40 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								This is frequently the case with [attribute directives ](guide/attribute-directives ).
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Directive consumers expect to bind to the name of the directive.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								For example, when you apply a directive with a `myClick`  selector to a `<div>`  tag,
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								you expect to bind to an event property that is also called `myClick` .
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								这是使用 [attribute 指令 ](guide/attribute-directives )时的常见情况。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								指令的使用者期望绑定到指令名。例如,在`<div>` 上用`myClick` 选择器应用指令时,
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								希望绑定的事件属性也叫`myClick` 。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.html"  region = "myClick"  title = "src/app/app.component.html"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								However, the directive name is often a poor choice for the name of a property within the directive class.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The directive name rarely describes what the property does.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The `myClick`  directive name is not a good name for a property that emits click messages.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								然而,在指令类中,直接用指令名作为自己的属性名通常都不是好的选择。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								指令名很少能描述这个属性是干嘛的。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								`myClick` 这个指令名对于用来发出 click 消息的属性就算不上一个好名字。 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Fortunately, you can have a public name for the property that meets conventional expectations,
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								while using a different name internally.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								In the example immediately above, you are actually binding *through the*  `myClick`  *alias*  to
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								the directive's own `clicks`  property.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								幸运的是,可以使用约定俗成的公开名字,同时在内部使用不同的名字。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								在上面例子中,实际上是把`myClick` 这个别名指向了指令自己的`clicks` 属性。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								You can specify the alias for the property name by passing it into the input/output decorator like this:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								把别名传进@Input/@Output装饰器 ,就可以为属性指定别名,就像这样:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/click.directive.ts"  region = "output-myClick"  title = "src/app/click.directive.ts"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-10 16:51:13 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< div  class = "l-sub-section" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-31 12:23:16 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								You can also alias property names in the `inputs`  and `outputs`  arrays.
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								You write a colon-delimited (`:` ) string with
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								the directive property name on the *left*  and the public alias on the *right* :
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								也可在`inputs` 和`outputs` 数组中为属性指定别名。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								可以写一个冒号 (`:` ) 分隔的字符串,*左侧*是指令中的属性名,*右侧*则是公开的别名。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/click.directive.ts"  region = "output-myClick2"  title = "src/app/click.directive.ts"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-10 16:51:13 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / div >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-10 16:51:13 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< hr / >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								{@a  expression-operators}
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								## Template expression operators
  
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								## 模板表达式操作符
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-31 12:23:16 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								The template expression language employs a subset of JavaScript syntax supplemented with a few special operators
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								for specific scenarios. The next sections cover two of these operators: _pipe_  and _safe navigation operator_ .
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								模板表达式语言使用了 JavaScript 语法的子集,并补充了几个用于特定场景的特殊操作符。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
										 
							
							
								  下面介绍其中的两个: 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								{@a  pipe}
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								### The pipe operator ( <span class="syntax">|</span> )
  
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								### 管道操作符 ( | )
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The result of an expression might require some transformation before you're ready to use it in a binding.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								For example, you might display a number as a currency, force text to uppercase, or filter a list and sort it.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								在绑定之前,表达式的结果可能需要一些转换。例如,可能希望把数字显示成金额、强制文本变成大写,或者过滤列表以及进行排序。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 15:36:40 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								Angular [pipes ](guide/pipes ) are a good choice for small transformations such as these.
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Pipes are simple functions that accept an input value and return a transformed value.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								They're easy to apply within template expressions, using the **pipe operator (`|`)** :
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								Angular [管道 ](guide/pipes )对像这样的小型转换来说是个明智的选择。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								管道是一个简单的函数,它接受一个输入值,并返回转换结果。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								它们很容易用于模板表达式中,只要使用**管道操作符 (`|` ) **就行了。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.html"  region = "pipes-1"  title = "src/app/app.component.html"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The pipe operator passes the result of an expression on the left to a pipe function on the right.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								管道操作符会把它左侧的表达式结果传给它右侧的管道函数。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								You can chain expressions through multiple pipes:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								还可以通过多个管道串联表达式:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.html"  region = "pipes-2"  title = "src/app/app.component.html"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								And you can also [apply parameters ](guide/pipes#parameterizing-a-pipe ) to a pipe:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								还能对它们使用参数:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.html"  region = "pipes-3"  title = "src/app/app.component.html"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								The `json`  pipe is particularly helpful for debugging bindings:
							 
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								`json` 管道对调试绑定特别有用: 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.html"  linenums = "false"  title = "src/app/app.component.html (pipes-json)"  region = "pipes-json" >  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								The generated output would look something like this
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								它生成的输出是这样的:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-30 20:04:18 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  language = "json" >  
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								  { "id": 0, "name": "Hercules", "emotion": "happy",
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								    "birthdate": "1970-02-25T08:00:00.000Z",
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								    "url": "http://www.imdb.com/title/tt0065832/",
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								    "rate": 325 }
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-10 16:51:13 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< hr / >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								{@a  safe-navigation-operator}
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								### The safe navigation operator ( <span class="syntax">?.</span> ) and null property paths
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								### 安全导航操作符 ( ?. ) 和空属性路径
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								The Angular **safe navigation operator (`?.`)**  is a fluent and convenient way to
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								guard against null and undefined values in property paths.
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Here it is, protecting against a view render failure if the `currentHero`  is null.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								Angular 的**安全导航操作符 (`?.` ) **是一种流畅而便利的方式,用来保护出现在属性路径中 null 和 undefined 值。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								下例中,当`currentHero` 为空时,保护视图渲染器,让它免于失败。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.html"  region = "safe-2"  title = "src/app/app.component.html"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								What happens when the following data bound `title`  property is null?
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								如果下列数据绑定中`title` 属性为空,会发生什么?
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.html"  region = "safe-1"  title = "src/app/app.component.html"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The view still renders but the displayed value is blank; you see only "The title is" with nothing after it.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								That is reasonable behavior. At least the app doesn't crash.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
										 
							
							
								这个视图仍然被渲染出来,但是显示的值是空;只能看到 “The title is”, 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								这是合理的行为。至少应用没有崩溃。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Suppose the template expression involves a property path, as in this next example
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								that displays the `name`  of a null hero.
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								假设模板表达式涉及属性路径,在下例中,显示一个空 (null) 英雄的`firstName` 。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-30 20:04:18 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  language = "html" >  
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								  The null hero's name is {{nullHero.name}}
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								JavaScript throws a null reference error, and so does Angular:
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
										 
							
							
								JavaScript 抛出了空引用错误, 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								  
							 
						 
					
						
							
								
									
										
										
										
											2017-03-30 20:04:18 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  format = "nocode" >  
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								  TypeError: Cannot read property 'name' of null in [null].
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Worse, the *entire view disappears* .
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								晕,*整个视图都不见了*。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								This would be reasonable behavior if the `hero`  property could never be null.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								If it must never be null and yet it is null,
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								that's a programming error that should be caught and fixed.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Throwing an exception is the right thing to do.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								如果确信`hero` 属性永远不可能为空,可以声称这是合理的行为。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								如果它必须不能为空,但它仍然是空值,实际上是制造了一个编程错误,它应该被捕获和修复。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								这种情况应该抛出异常。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								On the other hand, null values in the property path may be OK from time to time,
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								especially when the data are null now and will arrive eventually.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								另一方面,属性路径中的空值可能会时常发生,特别是当我们知道数据最终会出现。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								While waiting for data, the view should render without complaint, and
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								the null property path should display as blank just as the `title`  property does.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								当等待数据的时候,视图渲染器不应该抱怨,而应该把这个空属性路径显示为空白,就像上面`title` 属性那样。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Unfortunately, the app crashes when the `currentHero`  is null.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								不幸的是,当`currentHero` 为空的时候,应用崩溃了。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 15:36:40 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								You could code around that problem with [*ngIf ](guide/template-syntax#ngIf ).
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								可以通过用[NgIf ](guide/template-syntax#ngIf )代码环绕它来解决这个问题。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.html"  region = "safe-4"  title = "src/app/app.component.html"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								You could try to chain parts of the property path with `&&` , knowing that the expression bails out
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								when it encounters the first null.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								或者可以尝试通过`&&` 来把属性路径的各部分串起来,让它在遇到第一个空值的时候,就返回空。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.html"  region = "safe-5"  title = "src/app/app.component.html"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								These approaches have merit but can be cumbersome, especially if the property path is long.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Imagine guarding against a null somewhere in a long property path such as `a.b.c.d` .
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								这些方法都有价值,但是会显得笨重,特别是当这个属性路径非常长的时候。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								想象一下在一个很长的属性路径(如`a.b.c.d` )中对空值提供保护。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The Angular safe navigation operator (`?.` ) is a more fluent and convenient way to guard against nulls in property paths.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The expression bails out when it hits the first null value.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								The display is blank, but the app keeps rolling without errors.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								Angular 安全导航操作符 (`?.` ) 是在属性路径中保护空值的更加流畅、便利的方式。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								表达式会在它遇到第一个空值的时候跳出。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								显示是空的,但应用正常工作,而没有发生错误。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-03-11 13:44:25 +00:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.html"  region = "safe-6"  title = "src/app/app.component.html"  linenums = "false" >  
						 
					
						
							
								
									
										
										
										
											2017-03-27 16:08:53 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								It works perfectly with long property paths such as `a?.b?.c?.d` .
							 
						 
					
						
							
								
									
										
										
										
											2017-06-09 16:05:16 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-30 00:03:22 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								在像`a?.b?.c?.d` 这样的长属性路径中,它工作得很完美。< a  href = " #top -of-page" > back to top</ a > 
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-10 16:51:13 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< hr / >  
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-05-22 13:00:38 -07:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								{@a  non-null-assertion-operator}
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-05-22 13:00:38 -07:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								### The non-null assertion operator ( <span class="syntax">!</span> )
  
						 
					
						
							
								
									
										
										
										
											2017-03-30 20:04:18 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-08-05 12:47:14 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
										 
							
							
								### 非空断言操作符(<span class="syntax">!</span>)   
						 
					
						
							
								
									
										
										
										
											2017-08-04 14:06:15 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-06-12 12:50:47 -07:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								As of Typescript 2.0, you can enforce [strict null checking ](http://www.typescriptlang.org/docs/handbook/release-notes/typescript-2-0.html "Strict null checking in TypeScript" ) with the `--strictNullChecks`  flag. TypeScript then ensures that no variable is _unintentionally_  null or undefined.
							 
						 
					
						
							
								
									
										
										
										
											2017-05-22 13:00:38 -07:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-08-05 12:47:14 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								在 TypeScript 2.0 中,我们可以使用`--strictNullChecks` 标志强制开启[严格空值检查 ](http://www.typescriptlang.org/docs/handbook/release-notes/typescript-2-0.html "Strict null checking in TypeScript" )。TypeScript就会确保不存在意料之外的null或undefined。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-06-12 12:50:47 -07:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								In this mode, typed variables disallow null and undefined by default. The type checker throws an error if you leave a variable unassigned or try to assign null or undefined to a variable whose type disallows null and undefined.
							 
						 
					
						
							
								
									
										
										
										
											2017-05-22 13:00:38 -07:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-08-05 12:47:14 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
										 
							
							
								在这种模式下, , , , 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-10 10:01:54 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								The type checker also throws an error if it can't determine whether a variable will be null or undefined at runtime.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								You may know that can't happen but the type checker doesn't know.
							 
						 
					
						
							
								
									
										
										
										
											2017-06-12 12:50:47 -07:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								You tell the type checker that it can't happen by applying the post-fix
							 
						 
					
						
							
								
									
										
										
										
											2017-07-10 10:01:54 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								[_non-null assertion operator (!)_ ](http://www.typescriptlang.org/docs/handbook/release-notes/typescript-2-0.html#non-null-assertion-operator "Non-null assertion operator" ).
							 
						 
					
						
							
								
									
										
										
										
											2017-06-12 12:50:47 -07:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-08-05 12:47:14 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
										 
							
							
								如果类型检查器在运行期间无法确定一个变量是null或undefined, 
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								我们自己可能知道它不会为空,但类型检查器不知道。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								所以我们要告诉类型检查器,它不会为空,这时就要用到[*非空断言操作符* ](http://www.typescriptlang.org/docs/handbook/release-notes/typescript-2-0.html#non-null-assertion-operator "Non-null assertion operator" )。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-10 10:01:54 +01:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								The _Angular_  **non-null assertion operator (`!`)**  serves the same purpose in an Angular template.
							 
						 
					
						
							
								
									
										
										
										
											2017-04-01 01:57:13 +02:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-08-05 12:47:14 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								*Angular* 模板中的**非空断言操作符(`!` )也是同样的用途。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-06-12 12:50:47 -07:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								For example, after you use [*ngIf ](guide/template-syntax#ngIf ) to check that `hero`  is defined, you can assert that
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								`hero`  properties are also defined. 
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-08-05 12:47:14 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								例如,在用[*ngIf ](guide/template-syntax#ngIf )来检查过`hero` 是已定义的之后,就可以断言`hero` 属性一定是已定义的。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-05-22 13:00:38 -07:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								< code-example  path = "template-syntax/src/app/app.component.html"  region = "non-null-assertion-1"  title = "src/app/app.component.html"  linenums = "false" >  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								< / code-example >  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-06-12 12:50:47 -07:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								When the Angular compiler turns your template into TypeScript code,
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								it prevents TypeScript from reporting that `hero.name`  might be null or undefined.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-08-05 12:47:14 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								在 Angular 编译器把你的模板转换成 TypeScript 代码时,这个操作符会防止 TypeScript 报告 "`hero.name` 可能为null或undefined"的错误。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-06-12 12:50:47 -07:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								Unlike the [_safe navigation operator_ ](guide/template-syntax#safe-navigation-operator "Safe naviation operator (?. )"),
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								the **non-null assertion operator**  does not guard against null or undefined.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								Rather it tells the TypeScript type checker to suspend strict null checks for a specific property expression.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-08-05 12:47:14 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								与[_安全导航操作符_ ](guide/template-syntax#safe-navigation-operator "Safe naviation operator (?. )")不同的是,**非空断言操作符**不会防止出现null或undefined。
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								它只是告诉 TypeScript 的类型检查器对特定的属性表达式,不做 "严格空值检测"。
							 
						 
					
						
							
								
									
										
										
										
											2017-06-12 12:50:47 -07:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-08-05 12:47:14 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								You'll need this template operator when you turn on strict null checks. It's optional otherwise.
							 
						 
					
						
							
								
									
										
										
										
											2017-05-22 13:00:38 -07:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-08-05 12:47:14 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								如果我们打开了严格控制检测,那就要用到这个模板操作符,而其它情况下则是可选的。
							 
						 
					
						
							
								
									
										
										
										
											2017-07-30 22:11:36 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								< a  href = " #top -of-page" > back to top</ a >  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								< a  href = " #top -of-page" > 回到顶部</ a >  
						 
					
						
							
								
									
										
										
										
											2017-06-09 16:05:16 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								< hr / >  
						 
					
						
							
								
									
										
										
										
											2017-02-22 18:09:39 +00:00 
										
									 
								 
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								## Summary
  
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								## 小结
  
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-04-26 15:11:02 +03:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								You've completed this survey of template syntax.
							 
						 
					
						
							
								
									
										
										
										
											2017-07-23 11:51:25 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								Now it's time to put that knowledge to work on your own components and directives.
							 
						 
					
						
							
								
							 
							
								
							 
							
								 
							
								
									
								 
							
							
								
							 
						 
					
						
							
								
									
										
										
										
											2017-07-30 00:03:22 +08:00 
										
									 
								 
							 
							
								
									
										 
								
							 
							
								 
							
								
									
								 
							
							
								我们完成了模板语法的概述。现在,该把如何写组件和指令的知识投入到实际工作当中了。