Judy Bogart
Miško Hevery
parent
f8b9e61469
commit
644e7a28d8
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@ -52,16 +52,16 @@ When all dependencies are in place, `AppComponent` displays the user information
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## Limit service scope to a component subtree
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An Angular application has multiple injectors, arranged in a tree hierarchy that parallels the component tree.
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Each injector creates a singleton instance of a dependency.
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An Angular application has multiple injectors, arranged in a tree hierarchy that parallels the component tree.
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Each injector creates a singleton instance of a dependency.
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That same instance is injected wherever that injector provides that service.
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A particular service can be provided and created at any level of the injector hierarchy,
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which means that there can be multiple instances of a service if it is provided by multiple injectors.
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Dependencies provided by the root injector can be injected into *any* component *anywhere* in the application.
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In some cases, you might want to restrict service availability to a particular region of the application.
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Dependencies provided by the root injector can be injected into *any* component *anywhere* in the application.
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In some cases, you might want to restrict service availability to a particular region of the application.
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For instance, you might want to let users explicitly opt in to use a service,
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rather than letting the root injector provide it automatically.
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rather than letting the root injector provide it automatically.
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You can limit the scope of an injected service to a *branch* of the application hierarchy
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by providing that service *at the sub-root component for that branch*.
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@ -146,34 +146,34 @@ and confirm that the three `HeroBioComponent` instances have their own cached he
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When a class requires a dependency, that dependency is added to the constructor as a parameter.
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When Angular needs to instantiate the class, it calls upon the DI framework to supply the dependency.
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By default, the DI framework searches for a provider in the injector hierarchy,
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starting at the component's local injector of the component, and if necessary bubbling up
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starting at the component's local injector of the component, and if necessary bubbling up
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through the injector tree until it reaches the root injector.
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* The first injector configured with a provider supplies the dependency (a service instance or value) to the constructor.
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* The first injector configured with a provider supplies the dependency (a service instance or value) to the constructor.
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* If no provider is found in the root injector, the DI framework returns null to the constructor.
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There are a number of options for modifying the default search behavior, using _parameter decorators_
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on the service-valued parameters of a class constructor.
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on the service-valued parameters of a class constructor.
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{@a optional}
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### Make a dependency `@Optional` and limit search with `@Host`
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Dependencies can be registered at any level in the component hierarchy.
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When a component requests a dependency, Angular starts with that component's injector
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and walks up the injector tree until it finds the first suitable provider.
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Dependencies can be registered at any level in the component hierarchy.
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When a component requests a dependency, Angular starts with that component's injector
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and walks up the injector tree until it finds the first suitable provider.
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Angular throws an error if it can't find the dependency during that walk.
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In some cases, you need to limit the search or accommodate a missing dependency.
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You can modify Angular's search behavior with the `@Host` and `@Optional` qualifying
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decorators on a service-valued parameter of the component's constructor.
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decorators on a service-valued parameter of the component's constructor.
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* The `@Optional` property decorator tells Angular to return null when it can't find the dependency.
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* The `@Host` property decorator stops the upward search at the *host component*.
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The host component is typically the component requesting the dependency.
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However, when this component is projected into a *parent* component,
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* The `@Host` property decorator stops the upward search at the *host component*.
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The host component is typically the component requesting the dependency.
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However, when this component is projected into a *parent* component,
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that parent component becomes the host. The following example covers this second case.
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These decorators can be used individually or together, as shown in the example.
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@ -238,8 +238,8 @@ Here's `HeroBiosAndContactsComponent` in action.
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If you comment out the `@Host()` decorator, Angular walks up the injector ancestor tree
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until it finds the logger at the `AppComponent` level.
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The logger logic kicks in and the hero display updates
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until it finds the logger at the `AppComponent` level.
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The logger logic kicks in and the hero display updates
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with the "!!!" marker to indicate that the logger was found.
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<figure>
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@ -254,7 +254,7 @@ the app throws an exception when it cannot find the required logger at the host
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### Supply a custom provider with `@Inject`
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Using a custom provider allows you to provide a concrete implementation for implicit dependencies, such as built-in browser APIs. The following example uses an `InjectionToken` to provide the [localStorage](https://developer.mozilla.org/en-US/docs/Web/API/Window/localStorage) browser API as a dependency in the `BrowserStorageService`.
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Using a custom provider allows you to provide a concrete implementation for implicit dependencies, such as built-in browser APIs. The following example uses an `InjectionToken` to provide the [localStorage](https://developer.mozilla.org/en-US/docs/Web/API/Window/localStorage) browser API as a dependency in the `BrowserStorageService`.
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<code-example path="dependency-injection-in-action/src/app/storage.service.ts" header="src/app/storage.service.ts">
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@ -262,6 +262,8 @@ Using a custom provider allows you to provide a concrete implementation for impl
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The `factory` function returns the `localStorage` property that is attached to the browser window object. The `Inject` decorator is a constructor parameter used to specify a custom provider of a dependency. This custom provider can now be overridden during testing with a mock API of `localStorage` instead of interactive with real browser APIs.
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{@a skip}
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### Modify the provider search with `@Self` and `@SkipSelf`
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Providers can also be scoped by injector through constructor parameter decorators. The following example overrides the `BROWSER_STORAGE` token in the `Component` class `providers` with the `sessionStorage` browser API. The same `BrowserStorageService` is injected twice in the constructor, decorated with `@Self` and `@SkipSelf` to define which injector handles the provider dependency.
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@ -291,7 +293,7 @@ The directive sets the background to a highlight color when the user mouses over
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DOM element to which the directive is applied.
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Angular sets the constructor's `el` parameter to the injected `ElementRef`.
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(An `ElementRef` is a wrapper around a DOM element,
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(An `ElementRef` is a wrapper around a DOM element,
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whose `nativeElement` property exposes the DOM element for the directive to manipulate.)
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The sample code applies the directive's `myHighlight` attribute to two `<div>` tags,
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@ -332,7 +334,7 @@ Angular asks the injector for the service associated with `LoggerService`
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and assigns the returned value to the `logger` parameter.
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If the injector has already cached an instance of the service associated with the token,
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it provides that instance.
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it provides that instance.
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If it doesn't, it needs to make one using the provider associated with the token.
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<div class="alert is-helpful">
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@ -346,7 +348,7 @@ If the search fails, the injector throws an error—unless the request was [
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A new injector has no providers.
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Angular initializes the injectors it creates with a set of preferred providers.
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You have to configure providers for your own app-specific dependencies.
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You have to configure providers for your own app-specific dependencies.
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{@a defining-providers}
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@ -355,7 +357,7 @@ You have to configure providers for your own app-specific dependencies.
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### Defining providers
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A dependency can't always be created by the default method of instantiating a class.
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You learned about some other methods in [Dependency Providers](guide/dependency-injection-providers).
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You learned about some other methods in [Dependency Providers](guide/dependency-injection-providers).
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The following `HeroOfTheMonthComponent` example demonstrates many of the alternatives and why you need them.
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It's visually simple: a few properties and the logs produced by a logger.
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@ -364,7 +366,7 @@ It's visually simple: a few properties and the logs produced by a logger.
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</figure>
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The code behind it customizes how and where the DI framework provides dependencies.
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The use cases illustrate different ways to use the [*provide* object literal](guide/dependency-injection-providers#provide) to associate a definition object with a DI token.
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The use cases illustrate different ways to use the [*provide* object literal](guide/dependency-injection-providers#provide) to associate a definition object with a DI token.
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<code-example path="dependency-injection-in-action/src/app/hero-of-the-month.component.ts" region="hero-of-the-month" header="hero-of-the-month.component.ts">
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@ -389,13 +391,13 @@ The `HeroOfTheMonthComponent` example has two value providers.
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</code-example>
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* The first provides an existing instance of the `Hero` class to use for the `Hero` token, rather than
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requiring the injector to create a new instance with `new` or use its own cached instance.
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requiring the injector to create a new instance with `new` or use its own cached instance.
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Here, the token is the class itself.
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* The second specifies a literal string resource to use for the `TITLE` token.
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The `TITLE` provider token is *not* a class, but is instead a
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special kind of provider lookup key called an [injection token](guide/dependency-injection-in-action#injection-token), represented by
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an `InjectionToken` instance.
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an `InjectionToken` instance.
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You can use an injection token for any kind of provider but it's particularly
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helpful when the dependency is a simple value like a string, a number, or a function.
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@ -414,12 +416,12 @@ Other types of providers can create their values *lazily*; that is, when they're
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{@a useclass}
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#### Class providers: `useClass`
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#### Class providers: `useClass`
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The `useClass` provider key lets you create and return a new instance of the specified class.
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You can use this type of provider to substitute an *alternative implementation*
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for a common or default class.
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for a common or default class.
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The alternative implementation could, for example, implement a different strategy,
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extend the default class, or emulate the behavior of the real class in a test case.
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@ -502,7 +504,7 @@ This is illustrated in the following image, which displays the logging date.
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{@a usefactory}
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#### Factory providers: `useFactory`
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#### Factory providers: `useFactory`
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The `useFactory` provider key lets you create a dependency object by calling a factory function,
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as in the following example.
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@ -537,7 +539,7 @@ the passed-in state value and the injected services `Hero` and `HeroService`.
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The provider factory function (returned by `runnersUpFactory()`) returns the actual dependency object,
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the string of names.
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* The function takes a winning `Hero` and a `HeroService` as arguments.
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* The function takes a winning `Hero` and a `HeroService` as arguments.
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Angular supplies these arguments from injected values identified by
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the two *tokens* in the `deps` array.
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@ -588,7 +590,7 @@ But they did neither.
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`MinimalLogger` is used only as a dependency injection token.
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When you use a class this way, it's called a *class interface*.
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As mentioned in [DI Providers](guide/dependency-injection-providers#interface-not-valid-token),
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an interface is not a valid DI token because it is a TypeScript artifact that doesn't exist at run time.
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Use this abstract class interface to get the strong typing of an interface,
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@ -609,7 +611,7 @@ The `MinimalLogger` transpiles to this unoptimized, pre-minified JavaScript for
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</code-example>
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Notice that it doesn't have any members. It never grows no matter how many members you add to the class,
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as long as those members are typed but not implemented.
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as long as those members are typed but not implemented.
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Look again at the TypeScript `MinimalLogger` class to confirm that it has no implementation.
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@ -736,7 +738,7 @@ Break the circularity with `forwardRef`.
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</code-example>
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<!--- Waiting for good examples
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<!--- Waiting for good examples
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{@a directive-level-providers}
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@ -744,15 +746,15 @@ Break the circularity with `forwardRef`.
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## Element-level providers
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A component is a specialization of directive, and the `@Component()` decorator inherits the `providers` property from `@Directive`. The injector is at the element level, so a provider configured with any element-level injector is available to any component, directive, or pipe attached to the same element.
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A component is a specialization of directive, and the `@Component()` decorator inherits the `providers` property from `@Directive`. The injector is at the element level, so a provider configured with any element-level injector is available to any component, directive, or pipe attached to the same element.
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Here's a live example that implements a custom form control, taking advantage of an injector that is shared by a component and a directive on the same element.
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https://stackblitz.com/edit/basic-form-control
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The component, `custom-control`, configures a provider for the DI token `NG_VALUE_ACCESSOR`.
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The component, `custom-control`, configures a provider for the DI token `NG_VALUE_ACCESSOR`.
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In the template, the `FormControlName` directive is instantiated along with the custom component.
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It can inject the `NG_VALUE_ACCESSOR` dependency because they share the same injector.
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It can inject the `NG_VALUE_ACCESSOR` dependency because they share the same injector.
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(Notice that this example also makes use of `forwardRef()` to resolve a circularity in the definitions.)
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### Sharing a service among components
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@ -784,4 +786,3 @@ If you want to show only one of them, use the directive to make sure __??of what
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`<hero-overview heroCache></hero-overview>`
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--->
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@ -40,16 +40,15 @@ export abstract class LocationStrategy {
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/**
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* The `APP_BASE_HREF` token represents the base href to be used with the
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* {@link PathLocationStrategy}.
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*
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* If you're using {@link PathLocationStrategy}, you must provide a provider to a string
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* representing the URL prefix that should be preserved when generating and recognizing
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* URLs.
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* A predefined [DI token](guide/glossary#di-token) for the base href
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* to be used with the `PathLocationStrategy`.
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* The base href is the URL prefix that should be preserved when generating
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* and recognizing URLs.
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*
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* @usageNotes
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*
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* ### Example
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* The following example shows how to use this token to configure the root app injector
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* with a base href value, so that the DI framework can supply the dependency anywhere in the app.
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*
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* ```typescript
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* import {Component, NgModule} from '@angular/core';
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@ -30,17 +30,20 @@ export type InjectableProvider = ValueSansProvider | ExistingSansProvider |
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*/
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export interface InjectableDecorator {
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/**
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* A marker metadata that marks a class as available to `Injector` for creation.
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* Marks a class as available to `Injector` for creation.
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*
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* For more details, see the ["Dependency Injection Guide"](guide/dependency-injection).
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* @see [Introduction to Services and DI](guide/architecture-services)
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* @see [Dependency Injection Guide](guide/dependency-injection)
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*
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* @usageNotes
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* ### Example
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*
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* The following example shows how service classes are properly marked as
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* injectable.
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*
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* {@example core/di/ts/metadata_spec.ts region='Injectable'}
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*
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* `Injector` will throw an error when trying to instantiate a class that
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* does not have `@Injectable` marker, as shown in the example below.
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* `Injector` throws an error if it tries to instantiate a class that
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* is not decorated with `@Injectable`, as shown in the following example.
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*
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* {@example core/di/ts/metadata_spec.ts region='InjectableThrows'}
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*
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@ -56,7 +59,15 @@ export interface InjectableDecorator {
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*
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* @publicApi
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*/
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export interface Injectable { providedIn?: Type<any>|'root'|null; }
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export interface Injectable {
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/**
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* Determines which injectors will provide the injectable,
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* by either associating it with an @NgModule or other `InjectorType`,
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* or by specifying that this injectable should be provided in the
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* 'root' injector, which will be the application-level injector in most apps.
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*/
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providedIn?: Type<any>|'root'|null;
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}
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/**
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* Injectable decorator and metadata.
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*/
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export interface InjectDecorator {
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/**
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* A constructor parameter decorator that specifies a
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* custom provider of a dependency.
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* A parameter decorator on a dependency parameter of a class constructor
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* that specifies a custom provider of the dependency.
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*
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* @see ["Dependency Injection Guide"](guide/dependency-injection).
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* Learn more in the ["Dependency Injection Guide"](guide/dependency-injection).
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*
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* @usageNotes
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* The following example shows a class constructor that specifies a
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*
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* {@example core/di/ts/metadata_spec.ts region='Inject'}
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*
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* When `@Inject()` is not present, the `Injector` uses the type annotation of the
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* When `@Inject()` is not present, the injector uses the type annotation of the
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* parameter as the provider.
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*
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* {@example core/di/ts/metadata_spec.ts region='InjectWithoutDecorator'}
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@ -44,7 +44,7 @@ export interface InjectDecorator {
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*/
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export interface Inject {
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/**
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* Injector token that maps to the dependency to be injected.
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* A [DI token](guide/glossary#di-token) that maps to the dependency to be injected.
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*/
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token: any;
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}
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@ -65,14 +65,21 @@ export const Inject: InjectDecorator = makeParamDecorator('Inject', (token: any)
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*/
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export interface OptionalDecorator {
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/**
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* A constructor parameter decorator that marks a dependency as optional.
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*
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* A parameter decorator to be used on constructor parameters,
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* which marks the parameter as being an optional dependency.
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* The DI framework provides null if the dependency is not found.
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* For example, the following code allows the possibility of a null result:
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*
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* Can be used together with other parameter decorators
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* that modify how dependency injection operates.
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*
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* Learn more in the ["Dependency Injection Guide"](guide/dependency-injection).
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*
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* @usageNotes
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*
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* The following code allows the possibility of a null result:
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*
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* {@example core/di/ts/metadata_spec.ts region='Optional'}
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*
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* @see ["Dependency Injection Guide"](guide/dependency-injection).
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*/
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(): any;
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new (): Optional;
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@ -100,8 +107,13 @@ export const Optional: OptionalDecorator = makeParamDecorator('Optional');
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*/
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export interface SelfDecorator {
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/**
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* A constructor parameter decorator that tells the DI framework
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* to retrieve a dependency only from the local injector.
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* A parameter decorator to be used on constructor parameters,
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* which tells the DI framework to start dependency resolution from the local injector.
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*
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* Resolution works upward through the injector hierarchy, so the children
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* of this class must configure their own providers or be prepared for a null result.
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*
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* @usageNotes
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*
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* In the following example, the dependency can be resolved
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* by the local injector when instantiating the class itself, but not
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@ -109,8 +121,8 @@ export interface SelfDecorator {
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*
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* {@example core/di/ts/metadata_spec.ts region='Self'}
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*
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* @see ["Dependency Injection Guide"](guide/dependency-injection).
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*
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* @see `SkipSelf`
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* @see `Optional`
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*
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*/
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(): any;
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@ -140,16 +152,23 @@ export const Self: SelfDecorator = makeParamDecorator('Self');
|
|||
*/
|
||||
export interface SkipSelfDecorator {
|
||||
/**
|
||||
* A constructor parameter decorator that tells the DI framework
|
||||
* that dependency resolution should start from the parent injector.
|
||||
* A parameter decorator to be used on constructor parameters,
|
||||
* which tells the DI framework to start dependency resolution from the parent injector.
|
||||
* Resolution works upward through the injector hierarchy, so the local injector
|
||||
* is not checked for a provider.
|
||||
*
|
||||
* @usageNotes
|
||||
*
|
||||
* In the following example, the dependency can be resolved when
|
||||
* instantiating a child, but not when instantiating the class itself.
|
||||
*
|
||||
* {@example core/di/ts/metadata_spec.ts region='SkipSelf'}
|
||||
*
|
||||
* @see ["Dependency Injection Guide"](guide/dependency-injection).
|
||||
* Learn more in the
|
||||
* [Dependency Injection guide](guide/dependency-injection-in-action#skip).
|
||||
*
|
||||
* @see `Self`
|
||||
* @see `Optional`
|
||||
*
|
||||
*/
|
||||
(): any;
|
||||
|
|
@ -178,14 +197,17 @@ export const SkipSelf: SkipSelfDecorator = makeParamDecorator('SkipSelf');
|
|||
*/
|
||||
export interface HostDecorator {
|
||||
/**
|
||||
* A constructor parameter decorator that tells the DI framework
|
||||
* to retrieve a dependency from any injector until
|
||||
* reaching the host element of the current component.
|
||||
* A parameter decorator on a view-provider parameter of a class constructor
|
||||
* that tells the DI framework to resolve the view by checking injectors of child
|
||||
* elements, and stop when reaching the host element of the current component.
|
||||
*
|
||||
* @see ["Dependency Injection Guide"](guide/dependency-injection).
|
||||
* For an extended example, see
|
||||
* ["Dependency Injection Guide"](guide/dependency-injection-in-action#optional).
|
||||
*
|
||||
* @usageNotes
|
||||
*
|
||||
* The following shows use with the `@Optional` decorator, and allows for a null result.
|
||||
*
|
||||
* {@example core/di/ts/metadata_spec.ts region='Host'}
|
||||
*/
|
||||
(): any;
|
||||
|
|
|
|||
|
|
@ -11,15 +11,16 @@ import {Type} from '../interface/type';
|
|||
import {makePropDecorator} from '../util/decorators';
|
||||
|
||||
/**
|
||||
* This token can be used to create a virtual provider that will populate the
|
||||
* `entryComponents` fields of components and ng modules based on its `useValue`.
|
||||
* A DI token that you can use to create a virtual [provider](guide/glossary#provider)
|
||||
* that will populate the `entryComponents` field of components and NgModules
|
||||
* based on its `useValue` property value.
|
||||
* All components that are referenced in the `useValue` value (either directly
|
||||
* or in a nested array or map) will be added to the `entryComponents` property.
|
||||
* or in a nested array or map) are added to the `entryComponents` property.
|
||||
*
|
||||
* @usageNotes
|
||||
* ### Example
|
||||
*
|
||||
* The following example shows how the router can populate the `entryComponents`
|
||||
* field of an NgModule based on the router configuration which refers
|
||||
* field of an NgModule based on a router configuration that refers
|
||||
* to components.
|
||||
*
|
||||
* ```typescript
|
||||
|
|
@ -47,6 +48,48 @@ import {makePropDecorator} from '../util/decorators';
|
|||
*/
|
||||
export const ANALYZE_FOR_ENTRY_COMPONENTS = new InjectionToken<any>('AnalyzeForEntryComponents');
|
||||
|
||||
/**
|
||||
* Type of the `Attribute` decorator / constructor function.
|
||||
*
|
||||
* @publicApi
|
||||
*/
|
||||
export interface AttributeDecorator {
|
||||
/**
|
||||
* Specifies that a constant attribute value should be injected.
|
||||
*
|
||||
* The directive can inject constant string literals of host element attributes.
|
||||
*
|
||||
* @usageNotes
|
||||
* ### Example
|
||||
*
|
||||
* Suppose we have an `<input>` element and want to know its `type`.
|
||||
*
|
||||
* ```html
|
||||
* <input type="text">
|
||||
* ```
|
||||
*
|
||||
* A decorator can inject string literal `text` as in the following example.
|
||||
*
|
||||
* {@example core/ts/metadata/metadata.ts region='attributeMetadata'}
|
||||
*
|
||||
* @publicApi
|
||||
*/
|
||||
(name: string): any;
|
||||
new (name: string): Attribute;
|
||||
}
|
||||
|
||||
|
||||
/**
|
||||
* Type of the Attribute metadata.
|
||||
*
|
||||
* @publicApi
|
||||
*/
|
||||
export interface Attribute {
|
||||
/**
|
||||
* The name of the attribute to be injected into the constructor.
|
||||
*/
|
||||
attributeName?: string;
|
||||
}
|
||||
|
||||
/**
|
||||
* Type of the Query metadata.
|
||||
|
|
|
|||
Loading…
Reference in New Issue