The AppComponent
is doing everything at the moment.
In the beginning, it showed details of a single hero.
Then it became a master/detail form with both a list of heroes and the hero detail.
Soon there will be new requirements and capabilities.
You can't keep piling features on top of features in one component; that's not maintainable.
此刻,AppComponent
负责所有事。
起初,它只显示单个英雄的详情。然后,它变成了主从结构,同时显示英雄列表和一个英雄详情。
现在,我们很快又会有新需求了。
我们不能把这些需求全都放在一个组件中,否则将不可维护。
You'll need to break it up into sub-components, each focused on a specific task or workflow.
Eventually, the AppComponent
could become a simple shell that hosts those sub-components.
我们要把它拆分成一些子组件,每个子组件只聚焦在一个特定的任务或工作流上。
最后,AppComponent
将会变成一个简单的壳,用来作为那些子组件的宿主。
In this page, you'll take the first step in that direction by carving out the hero details into a separate, reusable component.
When you're done, the app should look like this
本章中,我们要做的第一步就是把英雄详情拆分到一个独立的、可复用的组件中。
做完这些,应用是这样的:
Where you left off
延续上一步教程
Before getting started on this page, verify that you have the following structure from earlier in the Tour of Heroes. If not, go back to the previous pages.
在继续《英雄指南》之前,先检查一下,是否已经有了如下目录结构。如果没有,回上一章,看看错过了哪里。
Keep the app transpiling and running while you build the Tour of Heroes
by entering the npm start
command in a terminal window
as you did before.
像以前一样,在终端窗口中输入npm start
命令,以便在构建《英雄指南》时保持持续转译和运行。
Make a hero detail component
制作英雄详情组件
Add a file named hero-detail.component.ts
to the app/
folder.
This file will hold the new HeroDetailComponent
.
往app/
文件夹下添加一个名叫hero-detail.component.ts
的文件。这个文件中会存放这个新的HeroDetailComponent
。
The file and component names follow the standard described in the Angular style guide.
文件名和组件名遵循风格指南中的标准方式。
The component class name should be written in upper camel case and end in the word "Component". The hero detail component class is
HeroDetailComponent
.组件的类名应该是大驼峰形式,并且以
Component
结尾。 因此英雄详情组件的类名是HeroDetailComponent
。The component file name should be spelled in lower dash case, each word separated by dashes, and end in
.component.ts
. TheHeroDetailComponent
class goes in thehero-detail.component.ts
file.组件的文件名应该是小写中线形式,每个单词之间用中线分隔,并且以
.component.ts
结尾。 因此HeroDetailComponent
类应该放在hero-detail.component.ts
文件中。
Start writing the HeroDetailComponent
as follows:
HeroDetailComponent
的代码如下:
app/hero-detail.component.ts (initial version)
To define a component, you always import the Component
symbol.
要定义一个组件,我们总是要先导入符号Component
。
The @Component
decorator provides the Angular metadata for the component.
The CSS selector name, hero-detail
, will match the element tag
that identifies this component within a parent component's template.
Near the end of this tutorial page,
you'll add a <hero-detail>
element to the AppComponent
template.
@Component
装饰器为组件提供了Angular元数据。
CSS选择器的名字hero-detail
会匹配元素的标签名,用于在父组件的模板中标记出当前组件的位置。
本章的最后,我们会把<hero-detail>
添加到AppComponent
的模板中。
Always export
the component class because you'll always import
it elsewhere.
总是export
这个组件类,因为你必然会在别处import
它。
Hero detail template
英雄详情的模板
To move the hero detail view to the HeroDetailComponent
,
cut the hero detail content from the bottom of the AppComponent
template
and paste it into a new template
property in the @Component
metadata.
要把英雄详情的视图移入HeroDetailComponent
,只要把英雄详情的 内容 从AppComponent
模板的底部剪切出来,
粘贴到@Component
元数据的template
属性中就可以了。
The HeroDetailComponent
has a hero, not a selected hero.
Replace the word, "selectedHero", with the word, "hero", everywhere in the template.
When you're done, the new template should look like this:
HeroDetailComponent
有一个 hero
属性,而不再是selectedHero
。
所以我们也要在模板中把所有的selectedHero
替换为hero
。
这些完成之后,新的模板是这样的:
src/app/hero-detail.component.ts (template)
Add the hero property
添加hero
属性
The HeroDetailComponent
template binds to the component's hero
property.
Add that property to the HeroDetailComponent
class like this:
HeroDetailComponent
模板绑定到了该组件的hero
属性上。
把这个属性添加到HeroDetailComponent
类上,就像这样:
src/app/hero-detail.component.ts (hero property)
The hero
property is typed as an instance of Hero
.
The Hero
class is still in the app.component.ts
file.
Now there are two components that need to reference the Hero
class.
The Angular style guide recommends one class per file anyway.
hero
属性的类型是Hero
。
Hero
类仍然在app.component.ts
文件中。
现在,有两个组件需要Hero
类的引用。
而Angular风格指南建议每个文件中只有一个类。
Move the Hero
class from app.component.ts
to its own hero.ts
file.
因此我们要把Hero
类从app.component.ts
移到它自己的hero.ts
文件中:
src/app/hero.ts
Now that the Hero
class is in its own file, the AppComponent
and the HeroDetailComponent
have to import it.
Add the following import
statement near the top of both the app.component.ts
and the hero-detail.component.ts
files.
现在,Hero
类有了自己的文件,AppComponent
和 HeroDetailComponent
就要import
它了。
把下列import
语句添加到app.component.ts
和hero-detail.component.ts
文件的顶部。
The hero property is an input property
hero属性是一个输入属性
Later in this page,
the parent AppComponent
will tell the child HeroDetailComponent
which hero to display
by binding its selectedHero
to the hero
property of the HeroDetailComponent
.
The binding will look like this:
在本章稍后的部分,
父组件AppComponent
会告诉子组件HeroDetailComponent
要显示哪个英雄,
告诉的方法是把它的selectedHero
属性绑定到HeroDetailComponent
的hero
属性上。
这种绑定是这样的:
Putting square brackets around the hero
property, to the left of the equal sign (=),
makes it the target of a property binding expression.
You must declare a target binding property to be an input property.
Otherwise, Angular rejects the binding and throws an error.
在等号的左边,是方括号围绕的hero
属性,这表示它是属性绑定表达式的目标。
我们要绑定到的目标属性必须是一个输入属性,否则Angular会拒绝绑定,并抛出一个错误。
First, amend the @angular/core
import statement to include the Input
symbol.
首先,修改@angular/core
导入语句,使其包含符号Input
。
src/app/hero-detail.component.ts (excerpt)
Then declare that hero
is an input property by
preceding it with the @Input
decorator that you imported earlier.
然后,通过在hero
属性前面加上@Input
装饰器,来表明它是一个输入属性。
src/app/hero-detail.component.ts (excerpt)
Read more about input properties in the Attribute Directives page.
要了解输入属性的更多知识,参见属性型指令页。
That's it. The hero
property is the only thing in the HeroDetailComponent
class.
现在,hero
属性是HeroDetailComponent
类中唯一的东西。
All it does is receive a hero object through its hero
input property and then bind to that property with its template.
它所做的一切就是通过它的输入属性hero
接收一个英雄对象,然后把这个属性绑定到自己的模板中。
Here's the complete HeroDetailComponent
.
下面是完整的HeroDetailComponent
:
src/app/hero-detail.component.ts
Declare HeroDetailComponent in the AppModule
在AppModule
中声明HeroDetailComponent
Every component must be declared in one—and only one—Angular module.
每个组件都必须在一个(且只有一个)Angular模块中声明。
Open app.module.ts
in your editor and import the HeroDetailComponent
so you can refer to it.
打开app.module.ts
并且导入HeroDetailComponent
,以便我们可以引用它。
src/app/app.module.ts
Add HeroDetailComponent
to the module's declarations
array.
把HeroDetailComponent
添加到该模块的declarations
数组中。
src/app/app.module.ts
In general, the declarations
array contains a list of application components, pipes, and directives that belong to the module.
A component must be declared in a module before other components can reference it.
This module declares only the two application components, AppComponent
and HeroDetailComponent
.
通常,declarations
数组包含应用中属于该模块的组件、管道和指令的列表。
组件在被其它组件引用之前必须先在一个模块中声明过。
这个模块只声明了两个组件:AppComponent
和 HeroDetailComponent
。
Add the HeroDetailComponent to the AppComponent
把HeroDetailComponent
添加到AppComponent
中
The AppComponent
is still a master/detail view.
It used to display the hero details on its own, before you cut out that portion of the template.
Now it will delegate to the HeroDetailComponent
.
AppComponent
仍然是主从视图。
在我们剪切模板之前,它自己显示英雄的详情。
现在,它委托给了HeroDetailComponent
。
Recall that hero-detail
is the CSS selector
in the HeroDetailComponent
metadata.
That's the tag name of the element that represents the HeroDetailComponent
.
回想一下,hero-detail
正是HeroDetailComponent
元数据中使用的 CSS selector
它是一个HTML元素的标签名,用于表示HeroDetailComponent
。
Add a <hero-detail>
element near the bottom of the AppComponent
template,
where the hero detail view used to be.
把<hero-detail>
元素添加到AppComponent
模板的底部,那里就是英雄详情视图所在的位置。
Coordinate the master AppComponent
with the HeroDetailComponent
by binding the selectedHero
property of the AppComponent
to the hero
property of the HeroDetailComponent
.
协调主视图AppComponent
与HeroDetailComponent
的方式是把AppComponent
的selectedHero
属性绑定到HeroDetailComponent
的hero
属性上。
app.component.ts (excerpt)
Now every time the selectedHero
changes, the HeroDetailComponent
gets a new hero to display.
每当selectedHero
变化时,HeroDetailComponent
就会显示一个新的英雄。
The revised AppComponent
template should look like this:
修改后的AppComponent
模板是这样的:
app.component.ts (excerpt)
What changed?
有哪些变化?
As before, whenever a user clicks on a hero name,
the hero detail appears below the hero list.
But now the HeroDetailView
is presenting those details.
仍然像以前一样,一旦用户点击了英雄的名字,英雄详情就会显示在英雄列表的下方。
不过现在改用HeroDetailView
来表示英雄详情了。
Refactoring the original AppComponent
into two components yields benefits, both now and in the future:
我们把原来的AppComponent
重构成了两个组件具有一些显著优点,无论是现在还是未来:
You simplified the
AppComponent
by reducing its responsibilities.通过缩减
AppComponent
的职责,我们简化了它。You can evolve the
HeroDetailComponent
into a rich hero editor without touching the parentAppComponent
.我们将来可以把
HeroDetailComponent
改进为功能更丰富的英雄编辑器,而不用动AppComponent
。You can evolve the
AppComponent
without touching the hero detail view.同样,我们也可以改进
AppComponent
而不用动英雄详情视图。You can re-use the
HeroDetailComponent
in the template of some future parent component.我们可以在未来的其它父组件的模板中复用
HeroDetailComponent
。
Review the app structure
审视本应用的代码结构
Verify that you have the following structure:
验证它是否已经有了如下结构:
Here are the code files discussed in this page.
下面是我们在本章讨论的代码文件:
The road you’ve travelled
走过的路
Here's what you achieved in this page:
来盘点一下我们已经构建了什么。
You created a reusable component.
我们创建了一个可复用组件
You learned how to make a component accept input.
我们学会了如何让一个组件接收输入
You learned to declare the required application directives in an Angular module. You listed the directives in the
NgModule
decorator'sdeclarations
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。You 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。
Your app should look like this
现在,应用应该变成了这样:
The road ahead
前方的路
The Tour of Heroes app is more reusable with shared components,
but its (mock) data is still hard coded within the AppComponent
.
That's not sustainable.
Data access should be refactored to a separate service
and shared among the components that need data.
通过抽取共享组件,我们的《英雄指南》变得更有复用性了,但在AppComponent
中,我们仍然使用着硬编码的模拟数据。显然,这种方式不能“可持续发展”。
我们要把数据访问逻辑重构到一个独立的服务中,并在需要数据的组件之间共享。
You’ll learn to create services in the next tutorial page.
在下一步,我们将学习如何创建服务。