修完了模板语法
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@ -68,7 +68,6 @@ block includes
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[为什么要加`@Injectable()`?](#injectable)
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* [Creating and registering a logger service](#logger-service)
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[创建并注册日志服务](#logger-service)
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@ -101,21 +100,16 @@ block includes
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[工厂提供商](#factory-provider)
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* [Dependency injection tokens](#dependency-injection-tokens)
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[依赖注入令牌](#dependency-injection-tokens)
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* [Non-class dependencies](#non-class-dependencies)
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[非"类"依赖](#non-class-dependencies)
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* [`InjectionToken`](#injection-token)
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[`InjectionToken`](#injection-token)
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* [Optional dependencies](#optional)
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[可选依赖](#optional)
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@ -141,7 +135,7 @@ block includes
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To understand why dependency injection is so important, consider an example without it.
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Imagine writing the following code:
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要想理解为什么依赖注入这么重要,就先来考虑不使用它的一个例子。想象下列代码:
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要理解为什么依赖注入这么重要,不妨先考虑不使用它的一个例子。想象下列代码:
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+makeExample('dependency-injection/ts/src/app/car/car-no-di.ts', 'car', 'src/app/car/car.ts (without DI)')
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@ -201,7 +195,7 @@ block includes
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Will a new instance of `Engine` make an asynchronous call to the server?
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You certainly don't want that going on during tests.
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当给`Car`类写测试的时候,我们被它那些隐藏的依赖所摆布。
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当给`Car`类写测试的时候,我们就会受制于它背后的那些依赖。
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能在测试环境中成功创建新的`Engine`吗?
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`Engine`自己又依赖什么?那些依赖本身又依赖什么?
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`Engine`的新实例会发起到服务器的异步调用吗?
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@ -228,7 +222,7 @@ block includes
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That's super easy. Change the `Car` constructor to a version with DI:
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<a id="ctor-injection"></a>
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答案超级简单。把`Car`的构造函数改造成使用 DI 的版本:
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答案非常简单。把`Car`的构造函数改造成使用 DI 的版本:
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+makeTabs(
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'dependency-injection/ts/src/app/car/car.ts, dependency-injection/ts/src/app/car/car-no-di.ts',
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@ -1496,6 +1490,6 @@ a#injection-token
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Avoid the problem altogether by defining components and services in separate files.
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在`forwardRef()`方法的帮助下,实际上也可以先定义组件,
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具体说明见这个[博客](http://blog.thoughtram.io/angular/2015/09/03/forward-references-in-angular-2.html)。
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具体说明见这篇[博客](http://blog.thoughtram.io/angular/2015/09/03/forward-references-in-angular-2.html)。
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但是为什么要先给自己找麻烦呢?
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还是通过在独立的文件中定义组件和服务,完全避免此问题吧。
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@ -317,16 +317,25 @@ a#expression-context
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the template variable name takes precedence, followed by a name in the directive's _context_,
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and, lastly, the component's member names.
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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。
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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。
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The previous example presents such a name collision. The component has a `hero`
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property and the `*ngFor` defines a `hero` template variable.
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The `hero` in `{{hero.name}}`
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refers to the template input variable, not the component's property.
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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。
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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。
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Template expressions cannot refer to anything in
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the global namespace. They can't refer to `window` or `document`. They
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can't call `console.log` or `Math.max`. They are restricted to referencing
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members of the expression context.
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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`。
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它们只能引用表达式上下文中的成员。
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a(href="#toc") back to top
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a(href="#toc") 回到顶部
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@ -1212,7 +1221,7 @@ a#one-time-initialization
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Imagine the following *malicious content*.
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假设下面的*恶毒内容*
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假设下面的*恶意内容*
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+makeExample('template-syntax/ts/src/app/app.component.ts', 'evil-title')(format=".")
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@ -1372,12 +1381,18 @@ a(href="#toc") 回到顶部
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其中后两部分是可选的。形如:`[class.class-name]`。
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The following examples show how to add and remove the application's "special" class
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with class bindings. Here's how to set the attribute without binding: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:
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with class bindings. Here's how to set the attribute without binding:
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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:
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+makeExample('template-syntax/ts/src/app/app.component.html', 'class-binding-1')(format=".")
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:marked
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You can replace that with a binding to a string of the desired class names; this is an all-or-nothing, replacement binding.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。
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You can replace that with a binding to a string of the desired class names; this is an all-or-nothing, replacement binding.
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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。
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(译注:即当 badCurly 有值时 class 这个 attribute 设置的内容会被完全覆盖)
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+makeExample('template-syntax/ts/src/app/app.component.html', 'class-binding-2')(format=".")
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:marked
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@ -1421,7 +1436,10 @@ a(href="#toc") 回到顶部
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+makeExample('template-syntax/ts/src/app/app.component.html', 'style-binding-1')(format=".")
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:marked
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Some style binding styles have aunit 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。
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Some style binding styles have a unit extension. The following example conditionally sets the font size in “em” and “%” units.
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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。
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+makeExample('template-syntax/ts/src/app/app.component.html', 'style-binding-2')(format=".")
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.l-sub-section
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@ -1937,7 +1955,10 @@ a#ngStyle
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+makeExample('template-syntax/ts/src/app/app.component.ts', 'setStyles')(format=".")
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:marked
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Adding an `ngStyle` property binding to `currentStyles` sets the element's styles accordingly:把`NgStyle`属性绑定到`currentStyles`,以据此设置此元素的样式:
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Adding an `ngStyle` property binding to `currentStyles` sets the element's styles accordingly:
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把`NgStyle`属性绑定到`currentStyles`,以据此设置此元素的样式:
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+makeExample('template-syntax/ts/src/app/app.component.html', 'NgStyle-2')(format=".")
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.l-sub-section
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@ -1954,32 +1975,49 @@ a#ngModel
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:marked
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### NgModel - Two-way binding to form elements with <span class="syntax">[(ngModel)]</span>
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### NgModel - 使用<span class="syntax">[(ngModel)]</span>双向绑定到表单元素
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When developing data entry forms, you often both display a data property and
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update that property when the user makes changes.
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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。
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Two-way data binding with the `NgModel` directive makes that easy. Here's an example:
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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:
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+makeExcerpt('src/app/app.component.html', 'NgModel-1', '')
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:marked
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#### _FormsModule_ is required to use _ngModel_
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#### 使用 `ngModel` 时需要 `FormsModule`
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Before using the `ngModel` directive in a two-way data binding,
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you must import the `FormsModule` and add it to the Angular module's `imports` list.
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Learn more about the `FormsModule` and `ngModel` in the
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[Forms](../guide/forms.html#ngModel) guide.
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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。
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要了解`FormsModule`和`ngModel`的更多知识,参见[表单](../guide/forms.html#ngModel)一章。
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Here's how to import the `FormsModule` to make `[(ngModel)]` available.
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导入`FormsModule`并让`[(ngModel)]`可用的代码如下:
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+makeExcerpt('src/app/app.module.1.ts (FormsModule import)', '')
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:marked
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#### Inside <span class="syntax">[(ngModel)]</span>
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#### <span class="syntax">[(ngModel)]</span>内幕
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Looking back at the `name` binding, note that
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you could have achieved the same result with separate bindings to
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the `<input>` element's `value` property and `input` event.
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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。
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+makeExample('template-syntax/ts/src/app/app.component.html', 'without-NgModel')(format=".")
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:marked
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@ -1987,8 +2025,13 @@ a#ngModel
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How do you extract the currently displayed text from the input box so you can update the data property?
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Who wants to look that up each time?
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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?
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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?
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That `ngModel` directive hides these onerous details behind its own `ngModel` input and `ngModelChange` output properties.
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`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。
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+makeExample('template-syntax/ts/src/app/app.component.html', 'NgModel-3')(format=".")
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.l-sub-section
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@ -1996,6 +2039,8 @@ a#ngModel
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The `ngModel` data property sets the element's value property and the `ngModelChange` event property
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listens for changes to the element's value.
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`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。
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The details are specific to each kind of element and therefore the `NgModel` directive only works for an element
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supported by a [ControlValueAccessor](../api/forms/index/ControlValueAccessor-interface.html)
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that adapts an element to this protocol.
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Angular provides *value accessors* for all of the basic HTML form elements and the
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[_Forms_](forms.html) guide shows how to bind to them.
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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/index/ControlValueAccessor-interface.html)的元素,
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它们能让元素适配本协议。
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`<input>`输入框正是其中之一。
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Angular为所有的基础HTML表单都提供了*值访问器(Value accessor)*,[*表单*](forms.html)一章展示了如何绑定它们。
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You can't apply `[(ngModel)]` to a non-form native element or a third-party custom component
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until you write a suitable *value accessor*,
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a technique that is beyond the scope of this guide.
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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。
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You don't need a _value accessor_ for an Angular component that you write because you
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can name the value and event properties
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to suit Angular's basic [two-way binding syntax](#two-way) and skip `NgModel` altogether.
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The [`sizer` shown above](#two-way) is an example of this technique.
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我们自己写的Angular组件不需要*值访问器*,因为我们可以让值和事件的属性名适应Angular基本的[双向绑定语法](#two-way),而不使用`NgModel`。
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[前面看过的`sizer`](#two-way)就是使用这种技巧的例子。
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:marked
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Separate `ngModel` bindings is an improvement over binding to the element's native properties. You can do better.
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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。
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You shouldn't have to mention the data property twice. Angular should be able to capture
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the component's data property and set it
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with a single declaration, which it can with the `[(ngModel)]` syntax:
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我们不用被迫两次引用这个数据属性,Angular可以捕获该元素的数据属性,并且通过一个简单的声明来设置它,这样它就可以使用`[(ngModel)]`语法了。
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+makeExample('template-syntax/ts/src/app/app.component.html', 'NgModel-1')(format=".")
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:marked
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Is `[(ngModel)]` all you need? Is there ever a reason to fall back to its expanded form?
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`[(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?
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The `[(ngModel)]` syntax can only _set_ a data-bound property.
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If you need to do something more or something different, you can write the expanded form.
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`[(ngModel)]`语法只能*设置*数据绑定属性。
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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。
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The following contrived example forces the input value to uppercase:
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下面这个生造的例子强制输入框的内容变成大写:
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+makeExample('template-syntax/ts/src/app/app.component.html', 'NgModel-4')(format=".")
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:marked
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Here are all variations in action, including the uppercase version:
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这里是所有这些变体的动画,包括这个大写转换的版本:
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figure.image-display
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img(src='/resources/images/devguide/template-syntax/ng-model-anim.gif' alt="NgModel variations")
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:marked
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## Built-in _structural_ directives
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## 内置*结构型*指令
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Structural directives are responsible for HTML layout.
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They shape or reshape the DOM's _structure_, typically by adding, removing, and manipulating
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the host elements to which they are attached.
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结构型指令的职责是HTML布局。
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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。
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The deep details of structural directives are covered in the
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[_Structural Directives_](structural-directives.html) guide
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where you'll learn:
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关于结构型指令的详情参见[*结构型指令*](structural-directives.html)一章,在那里我们将学到:
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* why you
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[_prefix the directive name with an asterisk_ (\*)](structural-directives.html#asterisk "The * in *ngIf").
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为什么要[给结构型指令的名字加上(\*)前缀?](structural-directives.html#asterisk "The * in *ngIf")
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* to use [`<ng-container>`](structural-directives.html#ngcontainer "<ng-container>")
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to group elements when there is no suitable host element for the directive.
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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。
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* how to write your own structural directive.
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如何写自己的结构型指令。
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* that you can only apply [one structural directive](structural-directives.html#one-per-element "one per host element") to an element.
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我们只能往一个元素上应用[一个结构型指令](structural-directives.html#one-per-element "one per host element")。
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_This_ section is an introduction to the common structural directives:
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*本节*是对常见结构型指令的简介:
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* [`NgIf`](#ngIf) - conditionally add or remove an element from the DOM
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[`NgIf`](#ngIf) - 根据条件把一个元素添加到DOM中或从DOM移除
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* [`NgFor`](#ngFor) - repeat a template for each item in a list
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[`NgFor`](#ngFor) - 对列表中的每个条目重复套用一个模板
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* [`NgSwitch`](#ngSwitch) - a set of directives that switch among alternative views
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[`NgSwitch`](#ngSwitch) - 一组指令,用于切换一组视图
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.l-hr
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a#ngIf
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:marked
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@ -2076,6 +2172,9 @@ a#ngIf
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that element (called the _host elment_).
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Bind the directive to a condition expression like `isActive` in this example.
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通过把`NgIf`指令应用到元素上(称为*宿主元素*),我们可以往DOM中添加或从DOM中移除这个元素。
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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。
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+makeExample('template-syntax/ts/src/app/app.component.html', 'NgIf-1')(format=".")
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.alert.is-critical
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||||
|
@ -2089,6 +2188,8 @@ a#ngIf
|
|||
When the expression is falsy, `NgIf` removes the `HeroDetailComponent`
|
||||
from the DOM, destroying that component and all of its sub-components.
|
||||
|
||||
当`isActive`表达式返回真值时,`NgIf`把`HeroDetailComponent`添加到DOM中;为假时,`NgIf`会从DOM中移除`HeroDetailComponent`,并销毁该组件及其所有子组件。
|
||||
|
||||
#### Show/hide is not the same thing
|
||||
|
||||
#### 这和显示/隐藏不是一回事
|
||||
|
@ -2126,6 +2227,8 @@ a#ngIf
|
|||
The show/hide technique is fine for a few elements with few children.
|
||||
You should be wary when hiding large component trees; `NgIf` may be the safer choice.
|
||||
|
||||
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。
|
||||
|
||||
#### Guard against null
|
||||
|
||||
#### 防范空指针错误
|
||||
|
@ -2234,24 +2337,39 @@ a#template-input-variables
|
|||
The `ngFor` directive iterates over the `heroes` array returned by the parent component's `heroes` property
|
||||
and sets `hero` to the current item from the array during each iteration.
|
||||
|
||||
`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。
|
||||
|
||||
You reference the `hero` input variable within the `ngFor` host element
|
||||
(and within its descendents) to access the hero's properties.
|
||||
Here it is referenced first in an interpolation
|
||||
and then passed in a binding to the `hero` property of the `<hero-detail>` component.
|
||||
|
||||
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。
|
||||
|
||||
+makeExample('template-syntax/ts/src/app/app.component.html', 'NgFor-1-2')(format=".")
|
||||
|
||||
:marked
|
||||
Learn more about _template input variables_ in the
|
||||
[_Structural Directives_](structural-directives.html#template-input-variable) guide.
|
||||
|
||||
要了解更多*模板输入变量*的知识,参见[*结构型指令*](structural-directives.html#template-input-variable)一章。
|
||||
|
||||
#### *ngFor with _index_
|
||||
|
||||
#### 带索引的`*ngFor`
|
||||
|
||||
The `index` property of the `NgFor` directive context returns the zero-based index of the item in each iteration.
|
||||
You can capture the `index` in a template input variable and use it in the template.
|
||||
|
||||
`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。
|
||||
|
||||
The next example captures the `index` in a variable named `i` and displays it with the hero name like this.
|
||||
|
||||
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。
|
||||
|
||||
+makeExample('template-syntax/ts/src/app/app.component.html', 'NgFor-3')(format=".")
|
||||
|
||||
.l-sub-section
|
||||
|
@ -2265,6 +2383,8 @@ a#trackBy
|
|||
:marked
|
||||
#### *ngFor with _trackBy_
|
||||
|
||||
#### 带`trackBy`的`*ngFor`
|
||||
|
||||
|
||||
The `NgFor` directive may perform poorly, especially with large lists.
|
||||
A small change to one item, an item removed, or an item added can trigger a cascade of DOM manipulations.
|
||||
|
@ -2331,13 +2451,21 @@ a#ngSwitch
|
|||
:marked
|
||||
### The _NgSwitch_ directives
|
||||
|
||||
### `NgSwitch`指令
|
||||
|
||||
*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.
|
||||
|
||||
`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。
|
||||
|
||||
*NgSwitch* is actually a set of three, cooperating directives:
|
||||
`NgSwitch`, `NgSwitchCase`, and `NgSwitchDefault` as seen in this example.
|
||||
|
||||
`NgSwitch`实际上包括三个相互协作的指令:`NgSwitch`、`NgSwitchCase` 和 `NgSwitchDefault`,例子如下:
|
||||
|
||||
+makeExample('template-syntax/ts/src/app/app.component.html', 'NgSwitch')(format=".")
|
||||
|
||||
figure.image-display
|
||||
|
@ -2347,26 +2475,47 @@ figure.image-display
|
|||
`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.
|
||||
|
||||
`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。
|
||||
|
||||
**Bind to `[ngSwitch]`**. You'll get an error if you try to set `*ngSwitch` because
|
||||
`NgSwitch` is an *attribute* directive, not a *structural* directive.
|
||||
It changes the behavior of its companion directives.
|
||||
It doesn't touch the DOM directly.
|
||||
|
||||
**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,而不会直接接触DOM结构。
|
||||
|
||||
**Bind to `*ngSwitchCase` and `*ngSwitchDefault`**.
|
||||
The `NgSwitchCase` and `NgSwitchDefault` directives are _structural_ directives
|
||||
because they add or remove elements from the DOM.
|
||||
|
||||
**绑定到`*ngSwitchCase`和`*ngSwitchDefault`**
|
||||
`NgSwitchCase` 和 `NgSwitchDefault` 指令都是*结构型指令*,因为它们会从DOM中添加或移除元素。
|
||||
|
||||
* `NgSwitchCase` adds its element to the DOM when its bound value equals the switch value.
|
||||
|
||||
`NgSwitchCase`会在它绑定到的值等于候选值时,把它所在的元素加入到DOM中。
|
||||
|
||||
* `NgSwitchDefault` adds its element to the DOM when there is no selected `NgSwitchCase`.
|
||||
|
||||
`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。
|
||||
|
||||
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.
|
||||
Each component has a `hero` [input property](#inputs-outputs "Input property")
|
||||
which is bound to the `currentHero` of the parent component.
|
||||
|
||||
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](#inputs-outputs "Input property")`hero`,它绑定到父组件的`currentHero`上。
|
||||
|
||||
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.
|
||||
|
||||
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:
|
||||
|
||||
+makeExample('template-syntax/ts/src/app/app.component.html', 'NgSwitch-div')(format=".")
|
||||
|
||||
a(href="#toc") back to top
|
||||
|
@ -2379,14 +2528,21 @@ a#ref-var
|
|||
:marked
|
||||
## Template reference variables ( <span class="syntax">#var</span> )
|
||||
|
||||
## 模板引用变量 ( <span class="syntax">#var</span> )
|
||||
|
||||
:marked
|
||||
A **template reference variable** is often a reference to a DOM element within a template.
|
||||
It can also be a reference to an Angular component or directive or a
|
||||
<a href="https://developer.mozilla.org/en-US/docs/Web/Web_Components" target="_blank" title="MDN: Web Components">web component</a>.
|
||||
|
||||
**模板引用变量**通常用来引用模板中的某个DOM元素,它还可以引用Angular组件或指令或<a href="https://developer.mozilla.org/en-US/docs/Web/Web_Components" target="_blank" title="MDN: Web Components">Web Component</a>。
|
||||
|
||||
Use the hash symbol (#) to declare a reference variable.
|
||||
The `#phone` declares a `phone` variable on an `<input>` element.
|
||||
|
||||
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。
|
||||
|
||||
+makeExample('template-syntax/ts/src/app/app.component.html', 'ref-var')(format=".")
|
||||
|
||||
:marked
|
||||
|
@ -2394,19 +2550,32 @@ a#ref-var
|
|||
The `phone` variable declared on this `<input>` is
|
||||
consumed in a `<button>` on the other side of the template
|
||||
|
||||
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。
|
||||
|
||||
+makeExample('template-syntax/ts/src/app/app.component.html', 'ref-phone')(format=".")
|
||||
|
||||
:marked
|
||||
### How a reference variable gets its value
|
||||
|
||||
### 模板引用变量怎么得到它的值?
|
||||
|
||||
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.
|
||||
|
||||
大多数情况下,Angular会把模板引用变量的值设置为声明它的那个元素。
|
||||
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。
|
||||
|
||||
The following is a *simplified* version of the form example in the [Forms](forms.html) guide.
|
||||
|
||||
下面是[表单](forms.html)一章中表单范例的*简化版*。
|
||||
|
||||
+makeExample('template-syntax/ts/src/app/hero-form.component.html')(format=".")
|
||||
|
||||
:marked
|
||||
|
@ -2414,29 +2583,50 @@ a#ref-var
|
|||
by a large amount of HTML.
|
||||
What is the value of `heroForm`?
|
||||
|
||||
模板引用变量`heroForm`在这个例子中出现了三次,中间隔着一大堆HTML。
|
||||
`heroForm`的值是什么?
|
||||
|
||||
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).
|
||||
The `heroForm` is actually a reference to an Angular [NgForm](../api/forms/index/NgForm-directive.html "API: NgForm")
|
||||
directive with the ability to track the value and validity of every control in the form.
|
||||
|
||||
如果你没有导入过`FormsModule`,Angular就不会控制这个表单,那么它就是一个[HTMLFormElement](https://developer.mozilla.org/en-US/docs/Web/API/HTMLFormElement)实例。
|
||||
这里的`heroForm`实际上是一个Angular [NgForm](../api/forms/index/NgForm-directive.html "API: NgForm") 指令的引用,
|
||||
因此具备了跟踪表单中的每个控件的值和有效性的能力。
|
||||
|
||||
The native `<form>` element doesn't have a `form` property.
|
||||
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
|
||||
to the parent component's `onSubmit` method.
|
||||
|
||||
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。
|
||||
|
||||
### Template reference variable warning notes
|
||||
|
||||
### 关于模板引用变量的提醒
|
||||
|
||||
A template _reference_ variable (`#phone`) is _not_ the same as a template _input_ variable (`let phone`)
|
||||
such as you might see in an [`*ngFor`](#template-input-variable).
|
||||
Learn the difference in the [_Structural Directives_](structural-directives.html#template-input-variable) guide.
|
||||
|
||||
模板*引用*变量 (`#phone`) 和[`*ngFor`](#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](structural-directives.html#template-input-variable)一章。
|
||||
|
||||
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.
|
||||
|
||||
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。
|
||||
|
||||
You can use the `ref-` prefix alternative to `#`.
|
||||
This example declares the `fax` variable as `ref-fax` instead of `#fax`.
|
||||
|
||||
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`。
|
||||
|
||||
+makeExample('template-syntax/ts/src/app/app.component.html', 'ref-fax')(format=".")
|
||||
|
||||
a(href="#toc") back to top
|
||||
|
@ -2600,9 +2790,12 @@ h3#aliasing-io
|
|||
This is frequently the case with [attribute directives](attribute-directives.html).
|
||||
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`.这是使用 [attribute 指令](attribute-directives.html)时的常见情况。
|
||||
you expect to bind to an event property that is also called `myClick`.
|
||||
|
||||
这是使用 [attribute 指令](attribute-directives.html)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`。
|
||||
|
||||
+makeExample('template-syntax/ts/src/app/app.component.html', 'myClick')(format=".")
|
||||
|
||||
:marked
|
||||
|
@ -2689,7 +2882,10 @@ a#pipe
|
|||
+makeExample('template-syntax/ts/src/app/app.component.html', 'pipes-2')(format=".")
|
||||
|
||||
:marked
|
||||
And you can also [apply parameters](./pipes.html#parameterizing-a-pipe) to a pipe:还能对它们使用参数:
|
||||
And you can also [apply parameters](./pipes.html#parameterizing-a-pipe) to a pipe:
|
||||
|
||||
还能对它们使用参数:
|
||||
|
||||
+makeExample('template-syntax/ts/src/app/app.component.html', 'pipes-3')(format=".")
|
||||
|
||||
:marked
|
||||
|
@ -2751,10 +2947,12 @@ a#safe-navigation-operator
|
|||
code-example(language="html").
|
||||
The null hero's name is {{nullHero.name}}
|
||||
|
||||
|
||||
:marked
|
||||
JavaScript throws a null reference error, and so does Angular:
|
||||
JavaScript 抛出了空引用错误,Angular 也是如此:code-example(format="nocode").
|
||||
|
||||
JavaScript 抛出了空引用错误,Angular 也是如此:
|
||||
|
||||
code-example(format="nocode").
|
||||
TypeError: Cannot read property 'name' of null in [null].
|
||||
|
||||
:marked
|
||||
|
|
Loading…
Reference in New Issue