dependency-injection translation - partial.
This commit is contained in:
Zhimin(Rex) YE
parent
1102c021f7
commit
ecc549e34e
|
|
@ -23,7 +23,7 @@ include ../_util-fns
|
|||
|
||||
[Limit service scope to a component subtree](#service-scope)
|
||||
|
||||
[服务作用范围限制在一个组件数内](#service-scope)
|
||||
[限制服务作用范围到一个组件支树](#service-scope)
|
||||
|
||||
[Multiple service instances (sandboxing)](#multiple-service-instances)
|
||||
|
||||
|
|
@ -31,7 +31,7 @@ include ../_util-fns
|
|||
|
||||
[Qualify dependency lookup with *@Optional* and *@Host*](#qualify-dependency-lookup)
|
||||
|
||||
[ 使用*@Optional*和*@Host*装饰来调用依赖](#qualify-dependency-lookup)
|
||||
[使用*@Optional*和*@Host*装饰来认证依赖调用过程](#qualify-dependency-lookup)
|
||||
|
||||
[Inject the component's DOM element](#component-element)
|
||||
|
||||
|
|
@ -98,10 +98,12 @@ include ../_util-fns
|
|||
A *provider* is something that can create or deliver a service.
|
||||
Angular creates a service instance from a class provider by "new-ing" it.
|
||||
Learn more about providers [below](#providers).
|
||||
一个*provider*
|
||||
一个*provider*是用来新建或者送交服务的。Angular从一个类provider里面，通过“new-ing”来新建服务实例的。从[下面](#providers)学习更多关于provders的知识。
|
||||
:marked
|
||||
Now that we've registered these services,
|
||||
Now that we've registered these services,
|
||||
Angular can inject them into the constructor of *any* component or service, *anywhere* in the application.
|
||||
|
||||
现在我们已经注册了这些服务，Angular能在应用程序的*任何地方*，将它们注入到*任何*组件和服务的构造函数里面。
|
||||
+makeExample('cb-dependency-injection/ts/app/hero-bios.component.ts','ctor','app/hero-bios.component.ts (component constructor injection)')(format='.')
|
||||
|
||||
+makeExample('cb-dependency-injection/ts/app/user-context.service.ts','ctor','app/user-context.service.ts (service constructor injection)')(format='.')
|
||||
|
|
@ -110,24 +112,37 @@ include ../_util-fns
|
|||
.l-main-section
|
||||
:marked
|
||||
## External module configuration
|
||||
## 外部模块设置
|
||||
We can register _certain_ module providers when bootstrapping rather than in the root application component.
|
||||
|
||||
与其在应用程序根组件里面，我们可以在引导过程中注册_某些_模块providers。
|
||||
|
||||
We'd do this when we expect to select or configure external modules that support our application
|
||||
but (a) aren't conceptually part of the application and (b) that we could change later without
|
||||
altering the essential logic of the application.
|
||||
|
||||
当使用支持我们的应用程序，并满足下面两个条件外来组件时，我们应该这样做（在引导过程中注册）：
|
||||
a）在概念上不是我们程序的一部分
|
||||
b）在未来，我们可能需要在不变化主要应用程序逻辑的情况下，更改或更换它。
|
||||
|
||||
For example, we might configure the Component Router with different
|
||||
[location strategies](../guide/router.html#location-strategy) based on environmental factors.
|
||||
The choice of location strategy doesn't matter to the application itself.
|
||||
|
||||
比如，我们可能用不同的[location strategies](../guide/router.html#location-strategy)，根据不同的环境因数设置不同的组件路由。这个location strategy不直接影响应用程序本身。
|
||||
|
||||
We could sneak in a fake HTTP backend with sample data during development rather than
|
||||
allow http calls to a remote server (that might not yet exist).
|
||||
We'll switch to the real backend in production.
|
||||
The application shouldn't know or care one way or the other.
|
||||
|
||||
在开发过程中，我们可以偷偷把一个假的带有例子数据的HTTP后端嵌入进来，来取代对一个远程服务器（可能还不存在）进行http查询。我们在产品发布时再切换到真正的后端。应用程序不需要知道，也不在乎哪个后端。
|
||||
|
||||
See both examples in the following `main.ts`
|
||||
where we list their service providers in an array in the second parameter of the `bootstrap` method.
|
||||
|
||||
在下面`main.ts`的两个例子中，我们在`bootstrap`类方法的第二个参数的数组中，我们列出了它们的service providers（服务提供者）。
|
||||
|
||||
+makeExample('cb-dependency-injection/ts/app/main.ts','bootstrap','app/main.ts')(format='.')
|
||||
|
||||
a(id="injectable")
|
||||
|
|
@ -135,21 +150,32 @@ a(id="nested-dependencies")
|
|||
.l-main-section
|
||||
:marked
|
||||
## *@Injectable* and nested service dependencies
|
||||
## *@Injectable*和嵌套服务依赖
|
||||
|
||||
The consumer of an injected service does not know how to create that service.
|
||||
It shouldn't care.
|
||||
It's the dependency injection's job to create and cache that service.
|
||||
|
||||
被注入服务的使用者不应该知道怎么创建这个服务。它不应该在在乎。新建和缓存这个服务是依赖注入的工作。
|
||||
|
||||
Sometimes a service depends on other services ... which may depend on yet other services.
|
||||
Resolving these nested dependencies in the correct order is also the framework's job.
|
||||
At each step, the consumer of dependencies simply declares what it requires in its constructor and the framework takes over.
|
||||
|
||||
有时候一个服务依赖其他服务...（其他服务）可能依赖另外的服务。按正确的顺序来解析这些嵌套依赖也是框架工具（Angualar 2依赖注入）的工作。
|
||||
在每一步，依赖的使用者只是在它的构造函数里简单地声明它需要什么，框架工具会做剩余的事情。
|
||||
|
||||
For example, we inject both the `LoggerService` and the `UserContext` in the `AppComponent`.
|
||||
|
||||
比如，我们在`AppComponent`里注入`LoggerService`和`UserContext`。
|
||||
+makeExample('cb-dependency-injection/ts/app/app.component.ts','ctor','app/app.component.ts')(format='.')
|
||||
|
||||
:marked
|
||||
The `UserContext` in turn has dependencies on both the `LoggerService` (again) and
|
||||
a `UserService` that gathers information about a particular user.
|
||||
|
||||
`UserContext`有两个依赖`LoggerService`（再次）和负责获取特定用户信息的`UserService`。
|
||||
|
||||
+makeExample('cb-dependency-injection/ts/app/user-context.service.ts','injectables','user-context.service.ts (injection)')(format='.')
|
||||
|
||||
:marked
|
||||
|
|
@ -158,107 +184,160 @@ a(id="nested-dependencies")
|
|||
The `UserContextService` needs the `LoggerService`, which the framework already has, and the `UserService`, which it has yet to create.
|
||||
The `UserService` has no dependencies so the dependency injection framework can just `new` one into existence.
|
||||
|
||||
当Angular新建一个`AppComponent`，依赖注入框架工具创建一个`LoggerService`的实例，和开始创建`UserContextService`。`UserContextService`需要框架工具已经有了的`LoggerService`和还没创建的`UserService`。
|
||||
`UserService`没有其他依赖，所以依赖注入框架工具可以直接`new`一个实例。
|
||||
|
||||
The beauty of dependency injection is that the author of `AppComponent` didn't care about any of this.
|
||||
The author simply declared what was needed in the constructor (`LoggerService` and `UserContextService`) and the framework did the rest.
|
||||
|
||||
依赖注入美丽的地方在于，`AppComponent`的作者不需要在乎这一切。作者只是在构造函数(`LoggerService`和`UserContextService`)里面简单地声明一下，框架工具来做剩下的工作。
|
||||
|
||||
Once all the dependencies are in place, the `AppComponent` displays the user information:
|
||||
|
||||
|
||||
一旦所有依赖都准备好了，`AppComponent`显示用户信息：
|
||||
figure.image-display
|
||||
img(src="/resources/images/cookbooks/dependency-injection/logged-in-user.png" alt="Logged In User")
|
||||
:marked
|
||||
### *@Injectable()*
|
||||
### *@Injectable()*
|
||||
Notice the `@Injectable()`decorator on the `UserContextService` class.
|
||||
|
||||
请注意在`UserContextService`类里面的`@Injectable()`装饰器。
|
||||
+makeExample('cb-dependency-injection/ts/app/user-context.service.ts','injectable','user-context.service.ts (@Injectable)')(format='.')
|
||||
:marked
|
||||
That decorator makes it possible for Angular to identify the types of its two dependencies, `LoggerService` and `UserService`.
|
||||
|
||||
该装饰器让Angular有能力辨认它的两个依赖 `LoggerService` 和 `UserService`。
|
||||
|
||||
Technically, the `@Injectable()`decorator is only _required_ for a service class that has _its own dependencies_.
|
||||
The `LoggerService` doesn't depend on anything. The logger would work if we omitted `@Injectable()`
|
||||
and the generated code would be slightly smaller.
|
||||
|
||||
技术上讲，这个`@Injectable()`装饰器只在一个服务类有_自己的依赖_的时候，才是_不可缺少_的。`LoggerService`不依赖任何东西。该日志在没有`@Injectable()`的时候应该也工作，生成的代码也小一些。
|
||||
But the service would break the moment we gave it a dependency and we'd have to go back and
|
||||
and add `@Injectable()` to fix it. We add `@Injectable()` from the start for the sake of consistency and to avoid future pain.
|
||||
|
||||
但是该服务在我们添加依赖给它的那一刻就会停止工作，要修复它，我们就必须要添加`@Injectable()`。为了保持一致性和防止将来的麻烦，我们从一开始就添加`@Injectable()`。
|
||||
|
||||
.alert.is-helpful
|
||||
:marked
|
||||
Although we recommend applying `@Injectable` to all service classes, do not feel bound by it.
|
||||
Some developers prefer to add it only where needed and that's a reasonable policy too.
|
||||
|
||||
虽然我们推荐在所有服务中使用`@Injectable`，你不需要一定要这么做。一些开发者宁可在需要添加的地方才添加，这也是一个合理的策略。
|
||||
|
||||
.l-sub-section
|
||||
:marked
|
||||
The `AppComponent` class had two dependencies as well but no `@Injectable()`.
|
||||
It didn't need `@Injectable()` because that component class has the `@Component` decorator.
|
||||
In Angular with TypeScript, a *single* decorator — *any* decorator — is sufficient to identify dependency types.
|
||||
|
||||
|
||||
|
||||
`AppComponent`类有两个依赖，但是没有`@Injectable()`。它不需要`@Injectable()`是因为组件类有`@Component`装饰器。
|
||||
在用TypeScript的Angular（应用程序）里，一个 *单独的* 装饰器 — *任何* 装饰器 — 来辨识依赖类别就足够了。
|
||||
<a id="service-scope"></a>
|
||||
.l-main-section
|
||||
:marked
|
||||
## Limit service scope to a component subtree
|
||||
|
||||
## 限制服务作用范围到一个组件支树
|
||||
All injected service dependencies are singletons meaning that,
|
||||
for a given dependency injector ("injector"), there is only one instance of service.
|
||||
|
||||
所有注入的服务依赖都是单例（singletons)，意思是，在任意一个依赖注入器("injector")中，每个服务只有一个唯一的实例。
|
||||
|
||||
But an Angular application has multiple dependency injectors, arranged in a tree hierarchy that parallels the component tree.
|
||||
So a particular service can be *provided* (and created) at any component level and multiple times
|
||||
if provided in multiple components.
|
||||
|
||||
但是一个Angular应用程序有多个依赖注入器，组织在一个与组件树平行的树形结构中。所以，在任何组件级别，一个特定的服务能被*提供*（和被建立）。如果在多个组件中注入，可以被新建或提供多次。
|
||||
|
||||
By default, a service dependency provided in one component is visible to all of its child components and
|
||||
Angular injects the same service instance into all child components that ask for that service.
|
||||
|
||||
默认情况下，在一个组件中注入的服务依赖，在所有该组件的子组件中都可见，而且Angular会注入同样的服务实例，到所有要求该服务的子组件中。
|
||||
|
||||
Accordingly, dependencies provided in the root `AppComponent` can be injected into *any* component *anywhere* in the application.
|
||||
|
||||
同样，在根部`AppComponent`提供的依赖能被注入到*任何*组件，到应用程序的*任何地方*。
|
||||
|
||||
That isn't always desireable.
|
||||
Sometimes we want to restrict service availability to a particular region of the application.
|
||||
|
||||
这不一定总是想要的。有时候我们想要把服务的有效性限制到应用程序的一个特定区域。
|
||||
|
||||
We can limit the scope of an injected service to a *branch* of the application hierarchy
|
||||
by providing that service *at the sub-root component for that branch*.
|
||||
Here we provide the `HeroService` to the `HeroesBaseComponent` by listing it in the `providers` array:
|
||||
|
||||
通过*在该分支的子级根部组件*中提供该服务， 我们能把一个注入服务的作用范围局限到一个应用程序结构的该*分支*中。
|
||||
这里我们通过列入`providers`数列，在`HeroesBaseComponent`中提供了`HeroService`：
|
||||
+makeExample('cb-dependency-injection/ts/app/sorted-heroes.component.ts','injection','app/sorted-heroes.component.ts (HeroesBaseComponent excerpt)')
|
||||
:marked
|
||||
When Angular creates the `HeroesBaseComponent`, it also creates a new instance of `HeroService`
|
||||
that is visible only to the component and its children (if any).
|
||||
|
||||
当Angular新建`HeroBaseComponent`的时候，它会同时建立一个`HeroService`实例，该实例只在该组件和其子组件（如果有）中可见。
|
||||
|
||||
We could also provide the `HeroService` to a *different* component elsewhere in the application.
|
||||
That would result in a *different* instance of the service, living in a *different* injector.
|
||||
|
||||
我们也可以在应用程序的另外的地方的*不同的*组件里提供`HeroService`。这样的结果是一个*不同的*该服务的实例，在一个*不同的*注入器内存在。
|
||||
.l-sub-section
|
||||
:marked
|
||||
We examples of such scoped `HeroService` singletons appear throughout the accompanying sample code,
|
||||
including the `HeroBiosComponent`, `HeroOfTheMonthComponent`, and `HeroesBaseComponent`.
|
||||
Each of these components has its own `HeroService` instance managing its own independent collection of heroes.
|
||||
|
||||
我们这个局限范围的`HeroService`单例的例子，贯穿伴随例子代码，包括`HeroBiosComponent`, `HeroOfTheMonthComponent`和`HeroBaseComponent`。
|
||||
这些组件中每个都有自己的`HeroService`实例，管理自己独立的英雄库。
|
||||
|
||||
.l-main-section
|
||||
.alert.is-helpful
|
||||
:marked
|
||||
### Take a break!
|
||||
### 休息一下！
|
||||
This much Dependency Injection knowledge may be all that many Angular developers
|
||||
ever need to build their applications. It doesn't always have to be more complicated.
|
||||
对一些Angular开发者来说，这么多依赖注入知识可能是所有需要的全部知识。不一定都要更加复杂。
|
||||
|
||||
<a id="multiple-service-instances"></a>
|
||||
.l-main-section
|
||||
:marked
|
||||
## Multiple service instances (sandboxing)
|
||||
## 多个服务实例（sandboxing)
|
||||
|
||||
Sometimes we want multiple instances of a service at *the same level of the component hierarchy*.
|
||||
|
||||
在*同一个级别的组件树*里，我们有时需要一个服务的多个实例。
|
||||
|
||||
A good example is a service that holds state for its companion component instance.
|
||||
We need a separate instance of the service for each component.
|
||||
Each service has its own work-state, isolated from the service-and-state of a different component.
|
||||
We call this *sandboxing* because each service and component instance has its own sandbox to play in.
|
||||
|
||||
一个管理自己伴随组件实例状态的服务是个好例子。
|
||||
对每个组件，我们都需要该服务的单独实例。每个服务有自己的工作-状态，与其他组件的服务-和-状态隔离。我们叫这个*sandboxing*，因为每个服务和组件实例都在自己的沙盒里运行。
|
||||
|
||||
<a id="hero-bios-component"></a>
|
||||
Imagine a `HeroBiosComponent` that presents three instances of the `HeroBioComponent`.
|
||||
|
||||
想象一下，一个`HeroBioComponent`，显示三个`HeroBioComponent`的实例。
|
||||
+makeExample('cb-dependency-injection/ts/app/hero-bios.component.ts','simple','ap/hero-bios.component.ts')
|
||||
:marked
|
||||
Each `HeroBioComponent` can edit a single hero's biography.
|
||||
A `HeroBioComponent` relies on a `HeroCacheService` to fetch, cache, and perform other persistence operations on that hero.
|
||||
|
||||
每个`HeroBioComponent`都能编辑一个英雄的生平。一个`HeroBioComponent`依赖一个`HeroCacheService`来对该英雄进行读取、缓存和执行其他持久性质的操作。
|
||||
+makeExample('cb-dependency-injection/ts/app/hero-cache.service.ts','service','app/hero-cache.service.ts')
|
||||
:marked
|
||||
Clearly the three instances of the `HeroBioComponent` can't share the same `HeroCacheService`.
|
||||
They'd be competing with each other to determine which hero to cache.
|
||||
|
||||
很明显，这三个`HeroBioComponent`实例不能共享一样的`HeroCacheService`。要不然它们会相互竞争冲突，取决于哪个英雄在缓存里面。
|
||||
|
||||
Each `HeroBioComponent` gets its *own* `HeroCacheService` instance
|
||||
by listing the `HeroCacheService` in its metadata `providers` array.
|
||||
|
||||
通过在自己的元数据（metadata)提供者(providers)数组里面列出`HeroCacheService`, 每个`HeroBioComponent`有自己*拥有*的`HeroCacheService`实例。
|
||||
+makeExample('cb-dependency-injection/ts/app/hero-bio.component.ts','component','app/hero-bio.component.ts')
|
||||
:marked
|
||||
The parent `HeroBiosComponent` binds a value to the `heroId`.
|
||||
|
|
@ -266,8 +345,12 @@ figure.image-display
|
|||
The getter for the `hero` property pulls the cached hero from the service.
|
||||
And the template displays this data-bound property.
|
||||
|
||||
此父级`HeroBioComponent`绑定一个变量到`HeroId`。`ngOnInit`传递该`id`到服务，服务再获取和缓存英雄。`hero`属性的getter从服务里面获取缓冲的英雄，并在模板里面显示该数据绑定的属性。
|
||||
|
||||
Find this example in [live code](/resources/live-examples/cb-dependency-injection/ts/plnkr.html)
|
||||
and confirm that the three `HeroBioComponent` instances have their own cached hero data.
|
||||
|
||||
在[在线代码](/resources/live-examples/cb-dependency-injection/ts/plnkr.html)找到这个例子，确认三个`HeroBioComponent`实例有自己拥有的缓冲的英雄数据。
|
||||
figure.image-display
|
||||
img(src="/resources/images/cookbooks/dependency-injection/hero-bios.png" alt="Bios")
|
||||
|
||||
|
|
@ -276,69 +359,107 @@ a(id="qualify-dependency-lookup")
|
|||
.l-main-section
|
||||
:marked
|
||||
## Qualify dependency lookup with *@Optional* and *@Host*
|
||||
## 使用*@Optional*和*@Host*装饰来认证依赖调用过程
|
||||
|
||||
We learned that dependencies can be registered at any level in the component hierarchy.
|
||||
|
||||
我们学习了依赖可以在任何组件级别注册依赖。
|
||||
|
||||
When a component requests a dependency, Angular starts with that component's injector and walks up the injector tree
|
||||
until it finds the first suitable provider. Angular throws an error if it can't find the dependency during that walk.
|
||||
|
||||
当一个组件请求一个依赖，Angular以该组件注入器开始，然后往上面以及的注入器树走，知道它找到第一个合适的provider。如果Angular不能再这个过程中找不到合适的依赖，它就抛出一个错误。
|
||||
|
||||
We *want* this behavior most of the time.
|
||||
But sometimes we need to limit the search and/or accommodate a missing dependency.
|
||||
We can modify Angular's search behavior with the `@Host` and `@Optional` qualifying decorators,
|
||||
used individually or together.
|
||||
|
||||
在大部分时候，我们*想要*这个行为。
|
||||
但是有时候，我们需要限制这个（依赖）搜索，并且/或者提供一个缺失的依赖。
|
||||
单独使用或者一起使用`@Host`和`@Optional`认证装饰器，我们能修改Angular的搜索行为。
|
||||
|
||||
The `@Optional` decorator tells Angular to continue when it can't find the dependency.
|
||||
Angular sets the injection parameter to `null` instead.
|
||||
|
||||
当Angular找不到依赖时，`@Optional`装饰器告诉Angular继续执行。Angular设置该注入参数为`null`（取代抛出错误得行为）。
|
||||
|
||||
The `@Host` decorator stops the upward search at the *host component*.
|
||||
|
||||
`@Host`装饰器将往上搜索的行为停止到*主持组件host component*
|
||||
|
||||
The host component is typically the component requesting the dependency.
|
||||
But when this component is projected into a *parent* component, that parent component becomes the host.
|
||||
We look at this second, more interesting case in our next example.
|
||||
|
||||
该主持组件一般为请求依赖的组件。但是当这个组件被投放到一个*父级*组件后，该父级组件变成了主持。我们考虑一会，更多有趣的案例还在后面的例子里。
|
||||
|
||||
### Demonstration
|
||||
### 示范
|
||||
The `HeroBiosAndContactsComponent` is a revision of the `HeroBiosComponent` that we looked at [above](#hero-bios-component).
|
||||
|
||||
该`HeroBiosAndContactsComponent`是[上面](#hero-bios-component)我们看过的`HeroBiosComponent`的修改版。
|
||||
+makeExample('cb-dependency-injection/ts/app/hero-bios.component.ts','hero-bios-and-contacts','app/hero-bios.component.ts (HeroBiosAndContactsComponent)')
|
||||
:marked
|
||||
Focus on the template:
|
||||
|
||||
注意它的模板：
|
||||
+makeExample('cb-dependency-injection/ts/app/hero-bios.component.ts','template')(format='.')
|
||||
:marked
|
||||
We've inserted a `<hero-contact>` element between the `<hero-bio>` tags.
|
||||
Angular *projects* (*transcludes*) the corresponding `HeroContactComponent` into the `HeroBioComponent` view,
|
||||
placing it in the `<ng-content>` slot of the `HeroBioComponent` template:
|
||||
|
||||
我们在`<hero-bio>`标签里插入了`<hero-contact>`元素。Angular*投放*（*transcludes*)对应的`HeroContactComponent`到`HeroBioComponent`视图里，将它放到`HeroBioComponent`模板的`<ng-content>`槽里面。
|
||||
+makeExample('cb-dependency-injection/ts/app/hero-bio.component.ts','template','app/hero-bio.component.ts (template)')(format='.')
|
||||
:marked
|
||||
It looks like this, with the heroe's telephone number from `HeroContactComponent` projected above the hero description:
|
||||
|
||||
从`HeroContactComponent`来的英雄的电话号码被投放到上面的英雄说明里面，看起来像这样：
|
||||
figure.image-display
|
||||
img(src="/resources/images/cookbooks/dependency-injection/hero-bio-and-content.png" alt="bio and contact")
|
||||
:marked
|
||||
Here's the `HeroContactComponent` which demonstrates the qualifying decorators that we're talking about in this section:
|
||||
|
||||
下面是`HeroContactComponent`，示范了我们在本节一直在讨论的认证装饰器(Qualifying decorators)：
|
||||
+makeExample('cb-dependency-injection/ts/app/hero-contact.component.ts','component','app/hero-contact.component.ts')
|
||||
:marked
|
||||
Focus on the constructor parameters
|
||||
请注意看构造函数的参数。
|
||||
+makeExample('cb-dependency-injection/ts/app/hero-contact.component.ts','ctor-params','app/hero-contact.component.ts')(format='.')
|
||||
:marked
|
||||
The `@Host()` function decorating the `_heroCache` property ensures that
|
||||
we get a reference to the cache service from the parent `HeroBioComponent`.
|
||||
Angular throws if the parent lacks that service, even if a component higher in the component tree happens to have that service.
|
||||
|
||||
`@Host()`函数装饰`_heroCache`属性，确保我们从其父级`HeroBioComponent`得到一个缓冲服务的引用。如果该父级不存在这个服务，Angular则抛错，就算组件树里再上级有一个组件拥有这个服务（Angular也抛错）。
|
||||
A second `@Host()` function decorates the `_loggerService` property.
|
||||
We know the only `LoggerService` instance in the app is provided at the `AppComponent` level.
|
||||
The host `HeroBioComponent` doesn't have its own `LoggerService` provider.
|
||||
|
||||
另外一个`@Host()`函数装饰`_loggerService`属性，我们知道在应用程序中，只有一个`LoggerService`实例，在`AppComponent`级别提供的。该主持`HeroBioComponent`没有自己的`LoggerService`provider。
|
||||
|
||||
Angular would throw an error if we hadn't also decorated the property with the `@Optional()` function.
|
||||
Thanks to `@Optional()`, Angular sets the `loggerService` to null and the rest of the component adapts.
|
||||
|
||||
如果我们没有同时使用`@Optional()`来装饰该属性的话，Angular会抛错。感谢`@Optional()`，Angular将`loggerService`设置为null，并继续改组件的执行。
|
||||
|
||||
.l-sub-section
|
||||
:marked
|
||||
We'll come back to the `elementRef` property shortly.
|
||||
|
||||
我们将很快回到`elementRef`属性。
|
||||
:marked
|
||||
Here's the `HeroBiosAndContactsComponent` in action.
|
||||
下面是`HeroBiosAndContactsComponent`的执行结果：
|
||||
figure.image-display
|
||||
img(src="/resources/images/cookbooks/dependency-injection/hero-bios-and-contacts.png" alt="Bios with contact into")
|
||||
:marked
|
||||
If we comment out the `@Host()` decorator, Angular now walks up the injector ancestor tree
|
||||
until it finds the logger at the `AppComponent` level. The logger logic kicks in and the hero display updates
|
||||
with the gratuituous "!!!", indicating that the logger was found.
|
||||
|
||||
如果我们
|
||||
figure.image-display
|
||||
img(src="/resources/images/cookbooks/dependency-injection/hero-bio-contact-no-host.png" alt="Without @Host")
|
||||
:marked
|
||||
|
|
|
|||
Loading…
Reference in New Issue