第四章翻译了一半儿
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Zhicheng Wang
parent
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@ -23,12 +23,12 @@ include ../_util-fns
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.l-main-section
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:marked
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## Where We Left Off
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## 我们从哪里出发
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## 我们在哪儿
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Before we continue with Part 2 of the Tour of Heroes,
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let’s verify we have the following structure after [Part 1](./toh-pt1.html).
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If not, we’ll need to go back to Part 1 and figure out what we missed.
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在继续《英雄之旅》的第二部分之前，我们先检查一下，完成第一部分之后，你是否已经有了如下目录结构。如果没有，你得先回到第一部分，看看缺了哪里。
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在继续《英雄之旅》的第二部分之前，我们先检查一下，完成[第一部分](./toh-pt1.html)之后，你是否已经有了如下目录结构。如果没有，你得先回到第一部分，看看缺了哪里。
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.filetree
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.file angular2-tour-of-heroes
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@ -48,7 +48,7 @@ include ../_util-fns
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### 让应用代码保持转译和运行
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We want to start the TypeScript compiler, have it watch for changes, and start our server. We'll do this by typing
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我们要启动TypeScript编译器，它会监视文件变更，并且启动开发服务器。我们只要敲：
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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。我们只要敲：
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code-example(format="." language="bash").
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npm start
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@ -14,10 +14,10 @@ include ../_util-fns
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.l-main-section
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:marked
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## Where We Left Off
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## 我们从哪里出发
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## 我们在哪儿
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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.
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在继续《英雄之旅》之前，我们先检查一下，完成第一部分之后，你是否已经有了如下目录结构。如果没有，你得先回到第一部分，看看缺了哪里。
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在继续《英雄之旅》之前，我们先检查一下，你是否已经有了如下目录结构。如果没有，你得先回上一章，看看缺了哪里。
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.filetree
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.file angular2-tour-of-heroes
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@ -37,7 +37,7 @@ include ../_util-fns
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### 让应用代码保持转译和运行
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We want to start the TypeScript compiler, have it watch for changes, and start our server. We'll do this by typing
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我们要启动TypeScript编译器，它会监视文件变更，并且启动开发服务器。我们只要敲：
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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。我们只要敲：
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code-example(format="." language="bash").
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npm start
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@ -2,28 +2,43 @@ include ../_util-fns
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:marked
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# Services
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# 服务
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The Tour of Heroes is evolving and we anticipate adding more components in the near future.
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《英雄之旅》继续前行。未来，我们准备添加更多的组件。
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Multiple components will need access to hero data and we don't want to copy and
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paste the same code over and over.
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Instead, we'll create a single reusable data service and learn to
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inject it in the components that need it.
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将会有更多的组件要访问英雄数据，但我们不想一遍又一遍的复制粘贴同样的代码。
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我们的替代方案是，创建一个单一的、可复用的数据服务，然后学习把它注入到那些想要用它的组件中去。
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Refactoring data access to a separate service keeps the component lean and focused on supporting the view.
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It also makes it easier to unit test the component with a mock service.
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重构数据访问代码，把它隔离到一个独立的服务中去，可以让组件保持精简，专注于为视图提供支持。
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如果想通过mock服务来对组件进行单元测试，在这种方式下也会变得更容易。
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Because data services are invariably asynchronous,
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we'll finish the chapter with a promise-based version of the data service.
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因为数据服务通常都是异步的，所以在本章的最后，我们会把它重构为基于Promise（即“承诺”，一种异步编程模式）的版本。
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:marked
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[Run the live example for part 4](/resources/live-examples/toh-4/ts/plnkr.html)
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[运行第四部分的鲜活范例](/resources/live-examples/toh-4/ts/plnkr.html)
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.l-main-section
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:marked
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## Where We Left Off
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## 我们在哪儿
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Before we continue with our Tour of Heroes, let’s verify we have the following structure.
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If not, we’ll need to go back and follow the previous chapters.
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在继续《英雄之旅》之前，我们先检查一下，你是否已经有了如下目录结构。如果没有，你得先回上一章，看看缺了哪里。
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.filetree
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.file angular2-tour-of-heroes
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.children
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@ -41,189 +56,322 @@ include ../_util-fns
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.file typings.json
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:marked
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### Keep the app transpiling and running
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### 让应用代码保持转译和运行
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Open a terminal/console window.
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Start the TypeScript compiler, watch for changes, and start our server by entering the command:
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打开terminal/console窗口，启动TypeScript编译器，它会监视文件变更，并启动开发服务器。我们只要敲：
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code-example(format="." language="bash").
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npm start
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:marked
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The application runs and updates automatically as we continue to build the Tour of Heroes.
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当我们继续构建《英雄之旅》时，应用会自动运行和更新。
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## Creating a Hero Service
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## 创建英雄服务
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Our stakeholders have shared their larger vision for our app.
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They tell us they want to show the heroes in various ways on different pages.
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We already can select a hero from a list.
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Soon we'll add a dashboard with the top performing heroes and create a separate view for editing hero details.
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All three views need hero data.
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客户描述了我们这个应用更广阔的图景。
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他们告诉我们，想要在不同的页面中用多种方式显示英雄。
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我们已经能从列表中选择一个英雄了。
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很快，我们将添加一个黑板报来表彰绩效最好的英雄，并且创建一个独立的视图来编辑英雄的详情。
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所有这些视图都需要英雄的数据。
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At the moment the `AppComponent` defines mock heroes for display.
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We have at least two objections.
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First, defining heroes is not the component's job.
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Second, we can't easily share that list of heroes with other components and views.
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目前，`AppComponent`显示的是自己定义的一个mock英雄数据。
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我们的改进点至少有两个：
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1. 定义英雄数据不应该是这个组件的任务。
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2. 要想把这个英雄列表数据共享给其它组件和视图可不容易。
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We can refactor this hero data acquisition business to a single service that provides heroes and
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share that service with all components that need heroes.
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我们可以把提供英雄数据的业务移交给一个单一的服务，它将提供英雄数据，并且把这个服务在所有需要英雄数据的组件之间共享。
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### Create the HeroService
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### 创建HeroService
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Create a file in the `app` folder called `hero.service.ts`.
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在`app`目录下创建一个名叫`hero.service.ts`的文件。
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.l-sub-section
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:marked
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We've adopted a convention in which we spell the name of a service in lowercase followed by `.service`.
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If the service name were multi-word, we'd spell the base filename with lower dash case (AKA "kebab-case").
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The `SpecialSuperHeroService` would be defined in the `special-super-hero.service.ts` file.
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我们遵循的文件命名约定是：服务名称的小写形式（基本名），加上`.service`后缀。
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如果服务名称包含多个字母，我们把基本名部分拼成中线格式（dash-case，也被称作烤串格式kebab-case）。
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于是，`SpecialSuperHeroService`服务应该被定义在`special-super-hero.service.ts`文件中。
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:marked
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We name the class `HeroService` and export it for others to import.
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+makeExample('toh-4/ts/app/hero.service.1.ts', 'empty-class', 'hero.service.ts (exported class)')(format=".")
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我们把这个类命名为`HeroService`，并且导出它，以供别人使用。
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+makeExample('toh-4/ts/app/hero.service.1.ts', 'empty-class', 'hero.service.ts (导出类)')(format=".")
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:marked
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### Injectable Services
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### 可注入的服务
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Notice that we imported the Angular `Injectable` function and applied that function as an `@Injectable()` decorator.
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注意，我们引入了Angular的`Injectable`函数，并且通过`@Injectable()`装饰器的形式使用这个函数。
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.callout.is-helpful
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:marked
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**Don't forget the parentheses!** Neglecting them leads to an error that's difficult to diagnose.
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**不要忘了写圆括号！** 如果忘了写，就会导致一个非常难以诊断的错误。
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:marked
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TypeScript sees the `@Injectable()` decorator and emits metadata about our service,
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metadata that Angular may need to inject other dependencies into this service.
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TypeScript看到`@Injectable()`装饰器时，就会记下关于这个服务的元数据。当Angular需要往这个服务中注入其它依赖时，就会用到这些元数据。
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The `HeroService` doesn't have any dependencies *at the moment*. Add the decorator anyway.
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It is a "best practice" to apply the `@Injectable()` decorator *from the start*
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both for consistency and for future-proofing.
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此刻，`HeroService`还不能拥有任何依赖。添加上这个装饰器。无论是从提高统一性还是减少变更的目的出发，都应该从一开始就加上`@Injectable()`装饰器，这是最佳实践。
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:marked
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### Getting Heroes
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### 获取英雄
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Add a `getHeroes` method stub.
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+makeExample('toh-4/ts/app/hero.service.1.ts', 'getHeroes-stub', 'hero.service.ts ( getHeroes stub)')(format=".")
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添加一个`getHeros`桩方法。
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+makeExample('toh-4/ts/app/hero.service.1.ts', 'getHeroes-stub', 'hero.service.ts (getHeroes桩方法)')(format=".")
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:marked
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We're holding back on the implementation for a moment to make an important point.
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在这个实现上暂停一会儿，我们来讲一个重点。
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The consumer of our service doesn't know how the service gets the data.
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Our `HeroService` could get `Hero` data from anywhere.
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It could get the data from a web service or local storage
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or from a mock data source.
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我们这个服务的消费者并不知道它具体如何获取数据。
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我们的`HeroService`服务可以从任何地方获得英雄的数据。
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它可能从网络服务器获取，可能从浏览器的局部存储区获取，也可能是写在源码中的mock数据。
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That's the beauty of removing data access from the component.
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We can change our minds about the implementation as often as we like,
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for whatever reason, without touching any of the components that need heroes.
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我们从组件中移除了数据访问代码，干得漂亮。
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这下子，我们可以随时改变数据访问的实现方式了。
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### Mock Heroes
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### Mock英雄数据
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We already have mock `Hero` data sitting in the `AppComponent`. It doesn't belong there. It doesn't belong *here* either.
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We'll move the mock data to its own file.
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我们已经在`AppComponent`组件中实现过mock的英雄数据了。它不该在那个文件，也不该在这个文件中！我们要把mock数据移到它自己的文件中去。
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Cut the `HEROES` array from `app.component.ts` and paste it to a new file in the `app` folder named `mock-heroes.ts`.
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We copy the `import {Hero} ...` statement as well because the heroes array uses the `Hero` class.
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+makeExample('toh-4/ts/app/mock-heroes.ts', null, 'mock-heroes.ts (Heroes array)')
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从`app.component.ts`文件中剪切`HEROS`数组，并且把它粘贴到`app`目录下一个名叫`mock-heroes.ts`的文件中。
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我们还要把`import {Hero}...`语句拷贝过来，因为我们的英雄数组用到了`Hero`类。
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+makeExample('toh-4/ts/app/mock-heroes.ts', null, 'mock-heroes.ts (英雄数组)')
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:marked
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We export the `HEROES` constant so we can import it elsewhere — such as our `HeroService`.
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我们导出`HEROES`常量，以便在其它地方导入它 —— 比如`HeroService`服务。
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Meanwhile, back in `app.component.ts` where we cut away the `HEROES` array,
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we leave behind an uninitialized `heroes` property:
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+makeExample('toh-4/ts/app/app.component.1.ts', 'heroes-prop', 'app.component.ts (heroes property)')(format=".")
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与此同时，回到我们刚刚剪切出`HEROES`数组的`app.component.ts`文件，我们留下了一个尚未初始化的`heroes`属性：
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+makeExample('toh-4/ts/app/app.component.1.ts', 'heroes-prop', 'app.component.ts (heroes属性)')(format=".")
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:marked
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### Return Mocked Heroes
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### 返回模拟的英雄数据
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Back in the `HeroService` we import the mock `HEROES` and return it from the `getHeroes` method.
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Our `HeroService` looks like this:
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回到`HeroService`，我们导入`HEROES`常量，并且在`getHeroes`方法中返回它。
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我们的`HeroService`服务看起来像这样：
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+makeExample('toh-4/ts/app/hero.service.1.ts', null, 'hero.service.ts')(format=".")
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:marked
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### Use the Hero Service
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### 使用HeroService服务
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We're ready to use the `HeroService` in other components starting with our `AppComponent`.
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我们已经在包括`AppComponent`在内的多个组件中使用了`HeroService`服务。
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We begin, as usual, by importing the thing we want to use, the `HeroService`.
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+makeExample('toh-4/ts/app/app.component.ts', 'hero-service-import', 'app.component.ts (import HeroService)')
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通常，我们会从导入要用到的东西开始，比如`HeroService`。
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+makeExample('toh-4/ts/app/app.component.ts', 'hero-service-import', 'app.component.ts (导入HeroService)')
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:marked
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Importing the service allows us to *reference* it in our code.
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How should the `AppComponent` acquire a runtime concrete `HeroService` instance?
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导入服务让我们可以在代码中引用它。
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`AppComponent`该如何在运行中获得一个具体的`HeroService`实例呢？
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### Do we *new* the *HeroService*? No way!
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### 我们要自己 *new* 出这个 *HeroService* 吗？没门！
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We could create a new instance of the `HeroService` with "new" like this:
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我们可以使用`new`关键字来创建`HeroService`的实例，就像这样：
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+makeExample('toh-4/ts/app/app.component.1.ts', 'new-service')(format=".")
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:marked
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That's a bad idea for several reasons including
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但这不是个好主意，理由很多，比如：
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* Our component has to know how to create a `HeroService`.
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If we ever change the `HeroService` constructor,
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we'll have to find every place we create the service and fix it.
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Running around patching code is error prone and adds to the test burden.
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* 我们的组件不得不了解如何取创建`HeroService`。
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如果有一天我们修改了`HeroService`的构造函数，我们不得不找出我们创建此服务的每一处代码，并且修改它。
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给代码打补丁的行为容易导致错误，而且增加了测试的负担。
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* We create a new service each time we use "new".
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What if the service should cache heroes and share that cache with others?
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We couldn't do that.
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* 我们每次使用`new`都会创建一个新的服务。
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如果这个服务需要缓存英雄列表，并且把这个缓存共享给别人，怎么办？
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没办法，这做不到。
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* We're locking the `AppComponent` into a specific implementation of the `HeroService`.
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It will be hard to switch implementations for different scenarios.
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Can we operate offline?
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Will we need different mocked versions under test?
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Not easy.
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* 我们把`AppComponent`锁定到了`HeroService`的一个特定实现中。
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我们很难在别的场景中把它更换为别的实现。
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比如，能离线操作吗？能在测试时使用不同的模拟版本吗？这可不容易。
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*What if ... what if ... Hey, we've got work to do!*
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* 如果……如果……嘿！我们有得忙了！
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We get it. Really we do.
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But it is so ridiculously easy to avoid these problems that there is no excuse for doing it wrong.
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我们有办法了，真的！这个办法真是简单得不可思议，它能解决这些问题，让你再也没有借口犯错误了。
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### Inject the *HeroService*
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### 注入 *HeroService*
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Two lines replace the one line of *new*:
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1. we add a constructor.
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1. we add to the component's `providers` metadata
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用两行代码代替用`new`时的一行：
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1. 添加一个构造函数
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1. 添加组件的`providers`元数据
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Here's the constructor:
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+makeExample('toh-4/ts/app/app.component.1.ts', 'ctor', 'app.component.ts (constructor)')
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下面就是这个构造函数：
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+makeExample('toh-4/ts/app/app.component.1.ts', 'ctor', 'app.component.ts (构造函数)')
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:marked
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The constructor itself does nothing. The parameter simultaneously
|
||||
defines a private `_heroService` property and identifies it as a `HeroService` injection site.
|
||||
|
||||
构造函数自己什么也不用做，它的参数同时定义了一个私有的`_heroService`属性，并且把它标记为注入`HeroService`的靶点。
|
||||
.l-sub-section
|
||||
:marked
|
||||
We prefix private variables with an underscore (_) to warn readers of our code
|
||||
that this variable is not part of the component's public API.
|
||||
|
||||
我们给私有变量添加下划线（_）前缀，用以警告阅读我们代码的人：这个变量不是组件的公开API的一部分。
|
||||
:marked
|
||||
Now Angular will know to supply an instance of the `HeroService` when it creates a new `AppComponent`.
|
||||
|
||||
现在，Angular将会知道，当它创建`AppComponent`实例时，需要先提供一个`HeroService`的实例。
|
||||
|
||||
Angular has to get that instance from somewhere. That's the role of the Angular *Dependency Injector*.
|
||||
The **Injector** has a **container** of previously created services.
|
||||
Either it finds and returns a pre-existing `HeroService` from its container or it creates a new instance, adds
|
||||
it to the container, and returns it to Angular.
|
||||
|
||||
Angular得想办法获得这个实例。这就是Angular *依赖注入器（Dependency Injector）* 扮演的角色。
|
||||
这个 **注入器** 有一个包括以前创建过的所有服务的 **容器** 。
|
||||
它既可以从容器中查找并返回一个已存在的`HeroService`实例，也可以创建一个新的实例，把它添加到容器中，然后把它返回给Angular。
|
||||
|
||||
.l-sub-section
|
||||
:marked
|
||||
Learn more about Dependency Injection in the [Dependency Injection](../guide/dependency-injection.html) chapter.
|
||||
|
||||
要了解关于依赖注入的更多知识，请参见[依赖注入](../guide/dependency-injection.html)一章。
|
||||
|
||||
:marked
|
||||
The *injector* does not know yet how to create a `HeroService`.
|
||||
If we ran our code now, Angular would fail with an error:
|
||||
|
||||
*注入器* 还不知道该如何创建`HeroService`。
|
||||
如果现在运行我们的代码，Angular会失败，并报错：
|
||||
code-example(format="." language="html").
|
||||
EXCEPTION: No provider for HeroService! (AppComponent -> HeroService)
|
||||
|
||||
EXCEPTION: No provider for HeroService! (AppComponent -> HeroService) —— 异常：没有HeroService的供应商(provider)！（AppComponent -> HeroService）
|
||||
:marked
|
||||
We have to teach the *injector* how to make a `HeroService` by registering a `HeroService` **provider**.
|
||||
Do that by adding the following `providers` array property to the bottom of the component metadata
|
||||
in the `@Component` call.
|
||||
|
||||
+makeExample('toh-4/ts/app/app.component.1.ts', 'providers', 'app.component.ts (providing HeroService)')
|
||||
我们还得注册一个`HeroService` **供应商** ，以便教 *注入器* 如何创建`HeroService`。
|
||||
要做到这一点，我们应该在`@Component`组件的元数据底部添加`providers`数组属性如下：
|
||||
+makeExample('toh-4/ts/app/app.component.1.ts', 'providers', 'app.component.ts (提供HeroService)')
|
||||
:marked
|
||||
The `providers` array tells Angular to create a fresh instance of the `HeroService` when it creates a new `AppComponent`.
|
||||
The `AppComponent` can use that service to get heroes and so can every child component of its component tree.
|
||||
|
||||
`providers`数组告诉Angular，在创建一个新的`AppComponent`时，也要创建一个`HeroService`的新鲜实例。
|
||||
`AppComponent`可以通过这个服务来获取英雄列表，在它组件树中的每一个子组件也可以这样做。
|
||||
<a id="child-component"></a>
|
||||
.l-sub-section
|
||||
:marked
|
||||
### Services and the component tree
|
||||
### 服务和组件树
|
||||
|
||||
Recall that the `AppComponent` creates an instance of `HeroDetail` by virtue of the
|
||||
`<my-hero-detail>` tag at the bottom of its template. That `HeroDetail` is a child of the `AppComponent`.
|
||||
|
||||
回忆一下，`AppComponent`在它的模板底部包含了一个`<my-hero-detail>`标记，于是创建了一个`HeroDetail`的实例。这个`HeroDetail`就叫做`AppComponent`的子组件。
|
||||
|
||||
If the `HeroDetailComponent` needed its parent component's `HeroService`,
|
||||
it would ask Angular to inject the service into its constructor which would look just like the one for `AppComponent`:
|
||||
+makeExample('toh-4/ts/app/app.component.1.ts', 'ctor', 'hero-detail.component.ts (constructor)')
|
||||
|
||||
如果`HeroDetailComponent`需要访问来自它父组件的`HeroService`服务，它可以要求Angular把这个服务注入到自己的构造函数中 —— 就像`AppComponent`中的做法一样。
|
||||
|
||||
+makeExample('toh-4/ts/app/app.component.1.ts', 'ctor', 'hero-detail.component.ts (构造函数)')
|
||||
:marked
|
||||
The `HeroDetailComponent` must *not* repeat its parent's `providers` array! Guess [why](#shadow-provider).
|
||||
|
||||
`HeroDetailComponent`不能再写一遍它父组件的`providers`数组！你猜这是[为什么](#shadow-provider)。
|
||||
|
||||
The `AppComponent` is the top level component of our application.
|
||||
There should be only one instance of that component and only one instance of the `HeroService` in our entire app.
|
||||
|
||||
`AppComponent`是我们应用的顶层组件。在我们的整个应用中，应该有唯一的一个顶层组件，应该由唯一的一个`HeroService`实例。
|
||||
:marked
|
||||
### *getHeroes* in the *AppComponent*
|
||||
### *AppComponent* 中的 *getHeroes*
|
||||
We've got the service in a `_heroService` private variable. Let's use it.
|
||||
|
||||
我们已经获得了此服务，并且把它存入了私有变量`_heroService`中。我们这就开始使用它。
|
||||
|
||||
We pause to think. We can call the service and get the data in one line.
|
||||
|
||||
停下来想一想。在同一行中，我们调用了服务并且获得了数据。
|
||||
+makeExample('toh-4/ts/app/app.component.1.ts', 'get-heroes')(format=".")
|
||||
:marked
|
||||
We don't really need a dedicated method to wrap one line. We write it anyway:
|
||||
|
|
|
|||
Loading…
Reference in New Issue