问角度4直通接口

EN

export interface MyInterface {
   sayHello();
}

@Injectable()
export class MyService implements MyInterface {
  sayHello()
  {
    throw new Error("Method not implemented.");
  }
}

export let MY_SERVICE = new InjectionToken<MyInterface>('MY_SERVICE');
  providers: [
    {
      provide: MY_SERVICE,
      useClass : MyService
    }
],`

@Component({
selector: 'app-root',
templateUrl: './app.component.html',
styleUrls: ['./app.component.css']
})
export class AppComponent {
title = 'app';
constructor(@Inject(MY_SERVICE) private myService : MyInterface) {
  }
}