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docs(hierarchical-di): clarify that component injector may be a proxy (#3248) 

closes #3242 and #3246
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Ward Bell 2017-02-13 15:37:31 -08:00 committed by GitHub
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19
public/docs/ts/latest/guide/hierarchical-dependency-injection.jade
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@ -20,11 +20,18 @@ block includes
In the [Dependency Injection](./dependency-injection.html) guide, In the [Dependency Injection](./dependency-injection.html) guide,
you learned how to configure a dependency injector and how to retrieve dependencies where you need them. you learned how to configure a dependency injector and how to retrieve dependencies where you need them.
In fact, there is no such thing as *the* injector. In fact, there is no such thing as ***the*** injector.
An application may have multiple injectors. An application may have multiple injectors.
An Angular application is a tree of components. Each component instance has its own injector! An Angular application is a tree of components. Each component instance has its own injector.
The tree of components parallels the tree of injectors. The tree of components parallels the tree of injectors.
.l-sub-section
:marked
The component's injector may be a _proxy_ for an ancestor injector higher in the component tree.
That's an implementation detail that improves efficiency.
You won't notice the difference and
your mental model should be that every component has its own injector.
:marked :marked
Consider this guide's variation on the Tour of Heroes application. Consider this guide's variation on the Tour of Heroes application.
At the top is the `AppComponent` which has some sub-components. At the top is the `AppComponent` which has some sub-components.
@ -37,14 +44,6 @@ figure.image-display
img(src="/resources/images/devguide/dependency-injection/component-hierarchy.png" alt="injector tree" width="600") img(src="/resources/images/devguide/dependency-injection/component-hierarchy.png" alt="injector tree" width="600")
:marked :marked
Angular doesn't actually _create_ a separate injector for each component.
Every component doesn't need its own injector and it would be horribly inefficient to create
masses of injectors for no good purpose.
But every component _has an injector_, even if it shares that injector with another component or with the injector of the root `AppModule`.
And there _may_ be multiple injector instances operating at different levels of the component tree
depending upon how the developer registers providers, which is the subject of this guide.
### Injector bubbling ### Injector bubbling
When a component requests a dependency, Angular tries to satisfy that dependency with a provider registered in that component's own injector. When a component requests a dependency, Angular tries to satisfy that dependency with a provider registered in that component's own injector.