typescript - Angular2 没有服务错误的提供者

Question

来自 Angular2 access global service without including it in every constructor我抓取了代码并将其稍微修改为:

@Injectable()
export class ApiService {
  constructor(public http: Http) {}

  get(url: string) {
    return http.get(url);
  }

}

@Injectable()
export abstract class BaseService {
  constructor(protected serv: ApiService) {}  
}

@Injectable()
export class MediaService extends BaseService {

  // Why do we need this?
  constructor(s: ApiService) {
    super(s)
  }

  makeCall() {
    this.serv.get("http://www.example.com/get_data")
  }

}

但是，当我尝试运行这段代码时，控制台出现错误:

NoProviderError {message: "No provider for ApiService! (App -> MediaService -> ApiService)", stack: "Error: DI Exception↵

我用 https://plnkr.co/edit/We2k9PDsYMVQWguMhhGl 的代码创建了一个 Plunkr

有谁知道导致这个错误的原因吗？

Answer 1

您还需要在 providers 属性中定义 ApiService。

@Component({
  selector: 'my-app',
  providers: [MediaService, ApiService], // <-----
  template: `
    <div>
      <h2>Hello {{name}}</h2>
    </div>
  `,
  directives: []
})
export class App {
  constructor(mediaService: MediaService) {
    this.name = 'Angular2'

    console.log('start');

    mediaService.makeCall();
  }
}

这是因为喷油器依赖组件。如果您想了解有关如何将服务注入(inject)服务的更多详细信息，可以查看以下问题:

• What's the best way to inject one service into another in angular 2 (Beta)?