include ../_util-fns

:marked
  Our app is growing.
  Use cases are flowing in for reusing components, passing data to components, and creating more reusable assets. Let's separate the heroes list from the hero details and make the details component reusable.

  我们的应用正在成长中。现在又有新的用例：重复使用组件，传递数据给组件并创建更多可复用的资源。
  我们来把英雄详情从英雄列表中拆分出来，让这个英雄详情组件可以被复用。

  Run the <live-example></live-example> for this part.

  运行这部分的<live-example>在线例子</live-example>。

.l-main-section
:marked
  ## Where We Left Off

  ## 延续上一步教程

  Before we continue with our Tour of Heroes, let’s verify we have the following structure. If not, we’ll need to go back and follow the previous chapters.

  在继续《英雄指南》之前，先来检查一下，你是否已经有了如下目录结构。如果没有，你得先回上一章，看看错过了哪里。

.filetree
  .file angular-tour-of-heroes
  .children
    .file app
    .children
      .file app.component.ts
      .file app.module.ts
      .file main.ts
    .file node_modules ...   
    .file index.html
    .file package.json
    .file styles.css
    .file systemjs.config.js
    .file tsconfig.json
:marked
  ### Keep the app transpiling and running

  ### 让应用代码保持转译和运行

  We want to start the TypeScript compiler, have it watch for changes, and start our server. We'll do this by typing

  我们要启动TypeScript编译器，它会监视文件变更，并启动开发服务器。只要敲：

code-example(language="bash").
  npm start

:marked
  This will keep the application running while we continue to build the Tour of Heroes.

  这个命令会在我们构建《英雄指南》的时候让应用得以持续运行。

  ## Making a Hero Detail Component

  ## 制作英雄详情组件

  Our heroes list and our hero details are in the same component in the same file.
  They're small now but each could grow. 
  We are sure to receive new requirements for one and not the other.
  Yet every change puts both components at risk and doubles the testing burden without benefit.
  If we had to reuse the hero details elsewhere in our app,
  the heroes list would tag along for the ride. 

  我们的英雄列表和英雄详情目前位于同一个文件的同一个组件中。
  现在它们还很小，但很快它们都会长大。
  我们将来肯定会收到新需求：针对这一个，却不能影响另一个。
  然而，每一个更改都会给这两个组件带来风险，并且带来双倍的测试负担，却没有任何好处。
  如果我们需要在应用的其它地方复用英雄详情组件，英雄列表组件也会跟着混进去。

  Our current component violates the
  [Single Responsibility Principle](https://blog.8thlight.com/uncle-bob/2014/05/08/SingleReponsibilityPrinciple.html).
  It's only a tutorial but we can still do things right &mdash; 
  especially if doing them right is easy and we learn how to build Angular apps in the process.

  我们当前的组件违反了[单一职责原则](https://blog.8thlight.com/uncle-bob/2014/05/08/SingleReponsibilityPrinciple.html)。
  虽然这只是一个教程，但我们还是得坚持做正确的事 —— 况且，做正确的事这么容易，我们何乐而不为呢？别忘了，我们正在学习的就是如何构建真正的Angular应用。

  Let’s break the hero details out into its own component.

  我们来把英雄详情拆分成一个独立的组件。

  ### Separating the Hero Detail Component

  ### 拆分英雄详情组件

  Add a new file named `hero-detail.component.ts` to the `app` folder and create `HeroDetailComponent` as follows.

  在`app`目录下添加一个名叫`hero-detail.component.ts`的文件，并且创建`HeroDetailComponent`。代码如下：

+makeExample('toh-3/ts/app/hero-detail.component.ts', 'v1', 'app/hero-detail.component.ts (initial version)')(format=".")

.l-sub-section
  :marked
    ### Naming conventions

    ### 命名约定

    We like to identify at a glance which classes are components and which files contain components.

    我们希望一眼就能看出哪些类是组件，以及哪些文件包含组件。

    Notice that  we have an `AppComponent` in a file named `app.component.ts` and our new
    `HeroDetailComponent` is in a file named `hero-detail.component.ts`. 

    你会注意到，在名叫`app.component.ts`的文件中有一个`AppComponent`组件，在名叫`hero-detail.component.ts`的文件中有一个`HeroDetailComponent`组件。

    All of our component names end in "Component".  All of our component file names end in ".component".

    我们的所有组件名都以`Component`结尾。所有组件的文件名都以`.component`结尾。

    We spell our file names in lower **[dash case](../guide/glossary.html#dash-case)**
    (AKA **[kebab-case](../guide/glossary.html#kebab-case)**) so we don't worry about
    case sensitivity on the server or in source control.

    这里我们使用小写**[中线命名法](../guide/glossary.html#dash-case)**(也叫**[烤串命名法](../guide/glossary.html#kebab-case)**)拼写文件名，
    所以不用担心它在服务器或者版本控制系统中出现大小写问题。

    <!-- TODO
    .l-sub-section
      :marked
        Learn more about naming conventions in the chapter [Naming Conventions]
    :marked
    -->
:marked
  We begin by importing the `Component` and `Input` decorators from Angular because we're going to need them soon.

  一开始，我们要先从Angular中导入`Component`和`Input`装饰器，因为马上就会用到它们。

  We create metadata with the `@Component` decorator where we 
  specify the selector name that identifies this component's element.
  Then we export the class to make it available to other components.

  我们使用`@Component`装饰器创建元数据。在元数据中，我们指定选择器的名字，用以标记此组件的元素。
  然后，我们导出这个组件类，以便其它组件可以使用它。

  When we finish here, we'll import it into `AppComponent` and create a corresponding `<my-hero-detail>`  element.

  做完这些，我们把它导入`AppComponent`组件，并创建相应的`<my-hero-detail>`元素。

:marked
  #### Hero Detail Template

  #### 英雄详情模板

  At the moment, the *Heroes* and *Hero Detail* views are combined in one template in `AppComponent`.
  Let’s **cut** the *Hero Detail* content from `AppComponent` and **paste** it into the new template property of  `HeroDetailComponent`.

  目前，`AppComponent`的*英雄列表*和*英雄详情*视图被组合在同一个模板中。
  让我们从`AppComponent`中**剪切**出*英雄详情*的内容，并且粘贴到`HeroDetailComponent`组件的`template`属性中。

  We previously bound to the `selectedHero.name` property of the `AppComponent`.
  Our `HeroDetailComponent` will have a `hero` property, not a `selectedHero` property.
  So we replace `selectedHero` with `hero` everywhere in our new template. That's our only change.
  The result looks like this:

  以前我们绑定到了`AppComponent`的`selectedHero.name`属性中。
  `HeroDetailComponent`组件将会有一个`hero`属性，而不是`selectedHero`属性。
  所以，我们要把模板中的所有`selectedHero`替换为`hero`。只改这些就够了。
  最终结果如下所示：

+makeExample('toh-3/ts/app/hero-detail.component.ts', 'template', 'app/hero-detail.component.ts (template)')(format=".")

:marked
  Now our hero detail layout exists only in the `HeroDetailComponent`.

  现在，我们的英雄详情布局只存在于`HeroDetailComponent`组件中了。

  #### Add the *hero* property

  #### 添加 *hero* 属性

  Let’s add that `hero` property we were talking about to the component class.

  我们这就添加刚刚所说的`hero`属性到组件类中。

+makeExample('toh-3/ts/app/hero-detail.component.ts', 'hero')

:marked
  Uh oh. We declared the `hero` property as type `Hero` but our `Hero` class is over in the `app.component.ts` file. 
  We have two components, each in their own file, that need to reference the `Hero` class. 

  啊哦！我们定义的`hero`属性是`Hero`类型的，但是我们的`Hero`类还在`app.component.ts`文件中。
  我们有了两个组件，它们都有各自的文件，并且都需要引用`Hero`类。

  We solve the problem by relocating the `Hero` class from `app.component.ts` to its own `hero.ts` file.

  要解决这个问题，我们也得从`app.component.ts`文件中把`Hero`类移到属于它自己的`hero.ts`文件中。

+makeExample('toh-3/ts/app/hero.ts', '', 'app/hero.ts')(format=".")

:marked
  We export the `Hero` class from `hero.ts` because we'll need to reference it in both component files. 
  Add the following import statement near the top of **both `app.component.ts` and `hero-detail.component.ts`**.

  我们得从`hero.ts`中导出`Hero`类，因为我们要从那些组件文件中引用它。
  在**`app.component.ts`和`hero-detail.component.ts`**的顶部添加下列import语句：

+makeExample('toh-3/ts/app/hero-detail.component.ts', 'hero-import')

:marked
  #### The *hero* property is an ***input***

  #### *hero*是一个***输入***属性

  The `HeroDetailComponent` must be told what hero to display. Who will tell it? The parent `AppComponent`!

  还得告诉`HeroDetailComponent`显示哪个英雄。谁告诉它呢？自然是父组件`AppComponent`了！

  The `AppComponent` knows which hero to show: the hero that the user selected from the list.
  The user's selection is in its `selectedHero` property.

  `AppComponent`确实知道该显示哪个英雄 —— 用户从列表中选中的那个。
  而这个英雄就是`selectedHero`属性的值。

  We will soon update the `AppComponent` template so that it binds its `selectedHero` property
  to the `hero` property of our `HeroDetailComponent`. The binding *might* look like this:

  我们马上升级`AppComponent`的模板，以便把该组件的`selectedHero`属性绑定到`HeroDetailComponent`组件的`hero`属性上。
  绑定看起来*可能*是这样的：

code-example(format=".").
  &lt;my-hero-detail [hero]="selectedHero">&lt;/my-hero-detail>

:marked
  Notice that the `hero` property is the ***target*** of a property binding &mdash; it's in square brackets to the left of the (=).

  注意，在等号(=)左边方括号中的这个`hero`是属性绑定的***目标***。

  Angular insists that we declare a ***target*** property to be an ***input*** property.
  If we don't, Angular rejects the binding and throws an error.

  Angular希望我们把***目标属性***定义成组件的***输入属性***，否则，Angular会拒绝绑定，并且抛出一个错误。

.l-sub-section
  :marked
    We explain input properties in more detail [here](../guide/attribute-directives.html#why-input) 
    where we also explain why *target* properties require this special treatment and 
    *source* properties do not.

    我们在[这里](../guide/attribute-directives.html#why-input)详细解释了输入属性，以及为什么*目标属性*需要“显式定义”这样的特殊待遇，而*源属性*却不需要。

:marked
  There are a couple of ways we can declare that `hero` is an *input*. 
  We'll do it the way we *prefer*, by annotating the `hero` property with the `@Input` decorator that we imported earlier.

  我们有几种方式把`hero`声明成*输入属性*。
  这里我们采用*首选*的方式：使用我们前面导入的`@Input`装饰器，为`hero`属性加上注解。

+makeExample('toh-3/ts/app/hero-detail.component.ts', 'hero-input')(format='.')

.l-sub-section
  :marked
    Learn more about the `@Input()` decorator in the 
    [Attribute Directives](../guide/attribute-directives.html#input) chapter.

    要了解`@Input()`装饰器的更多知识，参见[属性型指令](../guide/attribute-directives.html#input)一章。

.l-main-section
:marked
  ## Refresh the AppModule

  ## 更新AppModule

  We return to the `AppModule`, the application's root module, and teach it to use the `HeroDetailComponent`.

  回到`AppModule`，该应用的根模块，我们要教它使用`HeroDetailComponent`组件。

  We begin by importing the `HeroDetailComponent` so we can refer to it.

  我们先导入`HeroDetailComponent`组件，好让我们可以引用它。

+makeExample('toh-3/ts/app/app.module.ts', 'hero-detail-import')

:marked
  Then we add `HeroDetailComponent` to the `NgModule` decorator's `declarations` array.
  This array contains the list of all components, pipes, and directives that we created
  and that belong in our application's module.

  接下来，添加`HeroDetailComponent`到`NgModule`装饰器中的`declarations`数组。这个数组包含了所有属于本应用模块的，由我们亲自创建的组件、管道和指令。

+makeExample('toh-3/ts/app/app.module.ts', 'declarations')

.l-main-section
:marked
  ## Refresh the AppComponent

  ## 更新AppComponent
:marked
  Now that the application knows about our `HeroDetailComponent`, 
  find the location in the `AppComponent` template where we removed the *Hero Detail* content
  and add an element tag that represents the `HeroDetailComponent`.

  找到我们刚刚从模板中移除*英雄详情*的地方，放上用来表示`HeroDetailComponent`组件的HTML标签。

code-example(format=".").
  &lt;my-hero-detail>&lt;/my-hero-detail>

.l-sub-section
  :marked
    *my-hero-detail* is the name we set as the  `selector` in the `HeroDetailComponent` metadata.

    *my-hero-detail*是我们在`HeroDetailComponent`元数据中的`selector`属性所指定的名字。

:marked
 The two components won't coordinate until we bind the `selectedHero` property of the `AppComponent` 
 to the `HeroDetailComponent` element's `hero` property  like this:

 这两个组件目前还不能协同工作，直到我们把`AppComponent`组件的`selectedHero`属性和`HeroDetailComponent`组件的`hero`属性绑定在一起，就像这样：
code-example(format=".")
  &lt;my-hero-detail [hero]="selectedHero">&lt;/my-hero-detail>
:marked
  The `AppComponent`’s template should now look like this

  `AppComponent`的模板是这样的：

+makeExample('toh-3/ts/app/app.component.ts', 'hero-detail-template', 'app.component.ts (template)')(format='.')
:marked
  Thanks to the binding, the `HeroDetailComponent` should receive the hero from the `AppComponent` and display that hero's detail beneath the list.
  The detail should update every time the user picks a new hero.

  感谢数据绑定机制，`HeroDetailComponent`组件应该能从`AppComponent`组件中获取英雄数据，并且在列表的下方显示英雄的详情了。
  每当用户选中一个新的英雄时，详情信息应该随之更新。

:marked
  ### It works!

  ### 搞定！

  When we view our app in the browser we see the list of heroes.
  When we select a hero we can see the selected hero’s details. 

  当在浏览器中查看应用时，我们看到了英雄列表。
  当选中一个英雄时，还能看到所选英雄的详情。

  What's fundamentally new is that we can use this `HeroDetailComponent`
  to show hero details anywhere in the app.

  值得关注的进步是：我们可以在应用中的任何地方使用这个`HeroDetailComponent`组件来显示英雄详情了。

  We’ve created our first reusable component!

  我们创建了第一个可复用组件！

  ### Reviewing the App Structure

  ### 回顾应用结构

  Let’s verify that we have the following structure after all of our good refactoring in this chapter:

  来验证下吧，在本章中，经过这些漂亮的重构，我们应该得到了下列结构：

.filetree
  .file angular-tour-of-heroes
  .children
    .file app
    .children
      .file app.component.ts
      .file app.module.ts
      .file hero.ts
      .file hero-detail.component.ts
      .file main.ts
    .file node_modules ...
    .file index.html
    .file package.json
    .file tsconfig.json
:marked
  Here are the code files we discussed in this chapter.

  下面就是我们在本章讨论过的源码文件：

+makeTabs(`
  toh-3/ts/app/hero-detail.component.ts,
  toh-3/ts/app/app.component.ts,
  toh-3/ts/app/hero.ts,
  toh-3/ts/app/app.module.ts
  `,'',`
  app/hero-detail.component.ts,
  app/app.component.ts,
  app/hero.ts,
  app/app.module.ts
 `)

.l-main-section
:marked
  ## The Road We’ve Travelled

  ## 走过的路

  Let’s take stock of what we’ve built.

  来盘点一下我们已经构建完的部分。

  * We created a reusable component

  * 我们创建了一个可复用组件

  * We learned how to make a component accept input

  * 我们学会了如何让一个组件接收输入

  * We learned to declare the application directives we need in an Angular module. We
  list the directives in the `NgModule` decorator's `declarations` array.

  * 我们学会了在Angular模块中声明该应用所需的指令 —— 只要把这些指令列在`NgModule`装饰器的`declarations`数组中就可以了。

  * We learned to bind a parent component to a child component.

  * 我们学会了把父组件绑定到子组件。

  Run the <live-example></live-example> for this part.

  运行这部分的<live-example>在线例子</live-example>。

.l-main-section
:marked
  ## The Road Ahead

  ## 前方的路

  Our Tour of Heroes has become more reusable with shared components.

  通过抽取共享组件，我们的《英雄指南》变得更有复用性了。

  We're still getting our (mock) data within the `AppComponent`.
  That's not sustainable. 
  We should refactor data access to a separate service
  and share it among the components that need data. 

  但在`AppComponent`中，我们仍然使用着mock数据。
  显然，这种方式不能“可持续发展”。
  我们要把数据访问逻辑抽取到一个独立的服务中，并在需要数据的组件之间共享。

  We’ll learn to create services in the [next tutorial](toh-pt4.html) chapter.

  在[下一步](toh-pt4.html)，我们将学习如何创建服务。
