review displaying-data.jade
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@ -31,11 +31,12 @@ figure.image-display
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:marked
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## Showing component properties with interpolation
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## 使用插值表达式显示组件属性
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The easiest way to display a component property
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is to bind the property name through interpolation.
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With interpolation, we put the property name in the view template, enclosed in double curly braces: `{{myHero}}`.
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要显示组件的属性,最简单的方式就是通过插值表达式Interpolation来绑定属性名。
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要显示组件的属性,最简单的方式就是通过插值表达式(Interpolation)来绑定属性名。
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要使用插值表达式,就把属性名包裹在双重花括号里放进视图模板,如`{{myHero}}`。
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Let's build a small illustrative example together.
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@ -44,7 +45,7 @@ figure.image-display
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Create a new project folder (`displaying-data`) and follow the steps in the [QuickStart](../quickstart.html).
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创建一个新的项目文件夹(`displaying-data`),并且遵循[QuickStart](../quickstart.html)中的下列步骤。
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创建一个新的项目文件夹(`displaying-data`),并且完成[快速开始](../quickstart.html)中的步骤。
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include ../_quickstart_repo
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:marked
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@ -59,7 +60,7 @@ include ../_quickstart_repo
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:marked
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We added two properties to the formerly empty component: `title` and `myHero`.
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再把两个属性`title`和`myHero`添加到以这个空白组件中。
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再把两个属性`title`和`myHero`添加到之前空白的组件中。
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Our revised template displays the two component properties using double curly brace
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interpolation:
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@ -76,14 +77,14 @@ include ../_quickstart_repo
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much more readable HTML.
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模板是包在反引号(\`)中的一个多行字符串。
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反引号(\`) —— 不是单引号(') —— 有很多好用的特性。我们在这里用到的是它把一个字符串写在多行上的能力,这样我们就能写出更具可读性的HTML。
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反引号(\`) —— 不是单引号(') —— 有很多好用的特性。我们在这里用到的是它把一个字符串写在多行上的能力,这样我们的HTML模板更易于阅读。
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:marked
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Angular automatically pulls the value of the `title` and `myHero` properties from the component and
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inserts those values into the browser. Angular updates the display
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when these properties change.
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Angular会自动从组件中拉取`title`和`myHero`属性的值,并且把这些值插入浏览器中。一旦这些属性发生变化,Angular就会刷新显示。
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Angular会自动从组件中提取`title`和`myHero`属性的值,并且把这些值插入浏览器中。一旦这些属性发生变化,Angular就会自动刷新显示。
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.l-sub-section
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:marked
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More precisely, the redisplay occurs after some kind of asynchronous event related to
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@ -92,7 +93,7 @@ include ../_quickstart_repo
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But then the properties aren't changing on their own either. For the moment we must operate on faith.
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严格来说,“重新显示”是在某些与视图有关的异步事件之后发生的,比如:按键、定时器或收到异步`XHR`响应。本例中没有体现这一点。
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显然,属性肯定不会无缘无故的变化。但现在,我们只要先相信Angular会处理好就行了。
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很显然,属性肯定不会无缘无故的变化。但是目前我们只要先相信Angular会处理好就行了。
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:marked
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Notice that we haven't called **new** to create an instance of the `AppComponent` class.
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Angular is creating an instance for us. How?
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@ -103,7 +104,7 @@ include ../_quickstart_repo
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Remember back in QuickStart that we added the `<my-app>` element to the body of our `index.html`
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注意`@Component`装饰器中指定的CSS选择器`selector`,它指定了一个叫`my-app`的元素。
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回忆下,在QuickStart中,我们曾把一个`<my-app>`元素添加到`index.html`的`body`里。
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回忆下,在快速开始章节中,我们曾把一个`<my-app>`元素添加到`index.html`的`body`里。
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+makeExample('displaying-data/ts/index.html', 'my-app')(format=".")
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:marked
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inside the `<my-app>` tag.
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当我们通过`main.ts`中的`AppComponent`类启动时,Angular在`index.html`中查找一个`<my-app>`元素,
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找到它,实例化一个`AppComponent`,然后把这个实例渲染进`<my-app>`标签中。
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然后实例化一个`AppComponent`,并将其渲染进`<my-app>`标签中。
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We're ready to see changes in a running app by firing up the npm script that both compiles and serves our applications
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while watching for changes.
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We should see the title and hero name:
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我们应该能看到标题和英雄名变了:
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figure.image-display
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img(src="/resources/images/devguide/displaying-data/title-and-hero.png" alt="标题和英雄")
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:marked
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我们来回顾一下以前所做的决定,看看还有哪些其它选择。
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## Template inline or template file?
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## 行内模板还是模板文件?
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We can store our component's template in one of two places.
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Or we can define the template in a separate HTML file and link to it in
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the component metadata using the `@Component` decorator's `templateUrl` property.
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我们有两种地方可用来放组件模板。
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我们有两种地方可用来存放组件模板。
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我们可以使用`template`属性把它定义为 *内联Inline* 的,就像这里所做的一样。
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或者,可以把模板定义在一个独立的HTML文件中,并且在组件元数据中使用`@Component`装饰器的`templateUrl`属性链接到它。
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或者,可以把模板定义在一个独立的HTML文件中,并且在组件元数据`@Component`装饰器中的`templateUrl`属性链接到它。
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The choice between inline and separate HTML is a matter of taste,
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circumstances, and organization policy.
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无论用哪种风格,模板中的数据绑定在访问组件属性方面都是完全一样的。
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## Constructor or variable initialization?
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## 用构造函数进行初始化还是用变量?
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We initialized our component properties using variable assignment.
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.l-main-section
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:marked
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## Showing an array property with ***ngFor***
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## 使用***ngFor***显示数组属性
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We want to display a list of heroes. We begin by adding a mock heroes name array to the component,
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we should see heroes appearing in an unordered list.
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如果我们仍在运行着`npm start`命令,我们将看到英雄们的数据展现在了一个无序列表中。
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figure.image-display
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img(src="/resources/images/devguide/displaying-data/hero-names-list.png" alt="ngfor之后")
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.l-main-section
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:marked
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## Creating a class for the data
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## 为数据创建一个类
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We are defining our data directly inside our component.
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Although we won't do anything about that in this chapter, we'll make a mental note to fix this down the road.
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我们在组件内部直接定义了数据。
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对于演示来说,这还不错,但它当然不是最佳实践。它甚至算不上一个好的实践。
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对于演示来说,这还不错,但它显然不是最佳实践。它甚至算不上一个好的实践。
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我们在本章中先不管它,只是记下来,等将来再修复这个问题。
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At the moment, we're binding to an array of strings. We do that occasionally in real applications, but
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most of the time we're displaying objects — potentially instances of classes.
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现在,我们绑定到了一个字符串数组。在真实的应用中,这是特例。大多数时候,我们显示的是对象 —— 由类创建的实例 —— 的数组。
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现在,我们绑定到了一个字符串数组。在真实的应用中偶尔这么做。但绝大多数时候,我们显示的条目是对象 —— 很可能是类实例。
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Let's turn our array of hero names into an array of `Hero` objects. For that we'll need a `Hero` class.
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Create a new file in the `app/` folder called `hero.ts` with the following short bit of code.
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在`app/`目录下创建一个名叫`hero.ts`的新文件,内容如下:
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+makeExample('displaying-data/ts/app/hero.ts', null, 'app/hero.ts')(format = ".")
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:marked
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It might not look like we have properties, but we do. We're taking
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advantage of a TypeScript shortcut in our declaration of the constructor parameters.
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它可能看上去不像是有属性的,但确实有。我们正在使用TypeScript的高级特性:简写形式 —— 用构造函数的参数直接定义属性。
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它可能看上去不像是有属性的,但确实有。我们利用的是TypeScript提供的简写形式 —— 用构造函数的参数直接定义属性。
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Consider the first parameter:
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来看第一个参数:
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+makeExample('displaying-data/ts/app/hero.ts', 'id-parameter')
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:marked
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That brief syntax does a lot:
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这个简写语法做了很多:
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* declares a constructor parameter and its type
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* 定义了一个构造函数参数及其类型
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* declares a public property of the same name
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* 定义了一个同名的公开属性
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* initializes that property with the corresponding argument when we "new" an instance of the class
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* 当我们`new`出该类的一个实例时,把该属性初始化为相应的参数值
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.l-main-section
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:marked
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## Using the Hero class
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## 使用Hero类
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Let's redefine the `heroes` property in our component to return an array of these Hero objects
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and also set the `myHero` property with the first of these mock heroes.
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我们要把组件的`heroes`属性重定义为这些Hero对象的数组,并把这个数组中的第一项赋值给`myHero`属性。
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+makeExample('displaying-data/ts/app/app.component.3.ts', 'heroes', 'app.component.ts (节选)')(format=".")
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:marked
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At the moment it displays the entire `hero` object, which used to be a string value.
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Let's fix that so we interpolate the `hero.name` property.
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我们还得更新下模板。
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我们还得更新一下模板。
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现在它显示的是整个`hero`对象的值,这是被作为字符串值使用了。
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我们要修复它,所以,我们的插值表达式应该使用`hero.name`属性。
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+makeExample('displaying-data/ts/app/app.component.3.ts', 'template','app.component.ts (模板)')(format=".")
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:marked
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Our display looks the same, but now we know much better what a hero really is.
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从显示上看还是那样,但现在除了名字之外,我们对该英雄有了更多了解。
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从显示上看还是一样,但现在除了名字之外,我们有了更多英雄信息。
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<a id="ngIf"></a>
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.l-main-section
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:marked
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## Conditional display with NgIf
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## 通过NgIf进行条件显示
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Sometimes the app should display a view or a portion of a view only under specific circumstances.
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有时候,本应用应该只在特定情况下才显示视图或视图的一部分。
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有时候,应用应该只在特定情况下才显示视图或视图的一部分。
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In our example, we'd like to display a message if we have a large number of heroes — say, more than 3.
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在我们的例子中,如果有大量的英雄 —— 比如大于3位,我们会希望显示一条消息。
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在我们的例子中,假设如果有大量的英雄 —— 比如大于3位,我们希望显示一条消息。
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The Angular `ngIf` directive inserts or removes an element based on a truthy/falsey condition.
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We can see it in action by adding the following paragraph at the bottom of the template:
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Angular的`NgIf`指令会基于条件的真假来显示或移除一个元素。
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我们来亲自动手试一下,把下列语句加到模板的底部:
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+makeExample('displaying-data/ts/app/app.component.ts', 'message')
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.alert.is-important
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:marked
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不要忘了`*ngIf`中的前导星号(\*)。它是本语法中不可或缺的一部分。
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要学习关于此语法和`NgIf`的更多知识,请参见[模板语法](./template-syntax.html#ngIf)一章。
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:marked
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The [template expression](./template-syntax.html#template-expressions) inside the double quotes
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looks much like JavaScript and it _is_ much like JavaScript.
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Angular并不是在显示和隐藏这条消息,它是在从DOM中添加和移除这些元素。
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在这个范例中,它们几乎等价。但是如果我们想要有条件的包含或排除“一大堆”带着很多数据绑定的HTML,性能上的区别就会更加显著。
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:marked
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Try it out. Because the array has four items, the message should appear.
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Go back into `app.component.ts` and delete or comment out one of the elements from the hero array.
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.l-main-section
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:marked
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## Summary
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## 小结
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Now we know how to use:
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现在我们知道了如何使用:
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- **interpolation** with double curly braces to display a component property
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- 用带有双花括号的**插值表达式Interpolation**来显示组件的一个属性
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- **`ngFor`** to display a list of items
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- 用**`ngFor`**来显示条目列表
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- a TypeScript class to shape the **model data** for our component and display properties of that model
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- 用一个TypeScript类来为我们的组件描述**模型数据**并显示模型的各个属性。
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- **`ngIf`** to conditionally display a chunk of HTML based on a boolean expression
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- **`ngIf`**用来根据一个布尔表达式有条件的显示一段HTML
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Here's our final code:
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We’ll write our first test with inline JavaScript inside the body tag:
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我们接下来以内嵌JavaScript的形式在body表示里面,编写我们的第一个测试:
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我们接下来以内联JavaScript的形式在body表示里面,编写我们的第一个测试:
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+makeExample('testing/ts/unit-tests-0.html', 'body')(format='.')
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