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API > @angular/core

ClassProvider

配置此 Injector 以便为令牌返回 useClass 的实例。

Configures the Injector to return an instance of useClass for a token.

      
      interface ClassProvider extends ClassSansProvider {
  provide: any
  multi?: boolean

  // 继承自 core/ClassSansProvider
  useClass: Type<any>
}

参见

属性

属性说明
provide: any

注入令牌。（通常是 Type 或 InjectionToken 的实例，但也可以是 any 实例）。

An injection token. (Typically an instance of Type or InjectionToken, but can be any).

multi?: boolean

如果为 true，则注入器返回实例数组。这对于允许多个提供者散布在多个文件中，以向某个公共令牌提供配置信息时很有用。

When true, injector returns an array of instances. This is useful to allow multiple providers spread across many files to provide configuration information to a common token.

使用说明

      
      abstract class Shape {
  name!: string;
}

class Square extends Shape {
  name = 'square';
}

const injector = ReflectiveInjector.resolveAndCreate([{provide: Shape, useClass: Square}]);

const shape: Shape = injector.get(Shape);
expect(shape.name).toEqual('square');
expect(shape instanceof Square).toBe(true);

Note that following two providers are not equal:

      
      class Greeting {
  salutation = 'Hello';
}

class FormalGreeting extends Greeting {
  salutation = 'Greetings';
}

const injector = ReflectiveInjector.resolveAndCreate(
    [FormalGreeting, {provide: Greeting, useClass: FormalGreeting}]);

// The injector returns different instances.
// See: {provide: ?, useExisting: ?} if you want the same instance.
expect(injector.get(FormalGreeting)).not.toBe(injector.get(Greeting));

Multi-value example

      
      const locale = new InjectionToken<string[]>('locale');
const injector = Injector.create([
  {provide: locale, multi: true, useValue: 'en'},
  {provide: locale, multi: true, useValue: 'sk'},
]);

const locales: string[] = injector.get(locale);
expect(locales).toEqual(['en', 'sk']);