Question

我有一个身份验证服务，该服务会在发生错误时调用错误服务：

@Injectable({
providedIn: 'root'
})
export class AuthService {
  private loginUrl:string = '/api/auth/login';

  constructor(private httpClient:HttpClient, private errorService:ErrorService) { }

  public login(credentials) {
    let body = JSON.stringify(credentials);
    return this.httpClient.post(this.loginUrl, body, httpOptions)
    .pipe(
      catchError(this.errorService.handleError)
    )
  }
}

ErrorService调用MessageService，它将错误消息添加到消息视图中显示的消息数组中。

@Injectable({
providedIn: 'root'
})
export class ErrorService {

 constructor(private messageService:MessageService) { }

  public handleError(error: Response | any) {
    this.messageService.add('ERROR MESSAGE');
    return of([])
  }
}

如上所示，

MessageService被注入到ErrorService的构造函数中。但是，当ErrorService的handleError函数在上面显示的代码行中调用messageService.add（）函数时，MessageService被声明为未定义。

this.messageService.add('ERROR MESSAGE');

它会产生以下错误：

core.js:1624 ERROR TypeError: Cannot read property 'add' of undefined
at AuthService.push../src/app/shared/error/error.service.ts.ErrorService.handleError (error.service.ts:25)
at CatchSubscriber.push../node_modules/rxjs/_esm5/internal/operators/catchError.js.CatchSubscriber.error (catchError.js:33)

MessageService：

@Injectable({
  providedIn: 'root'
})
export class MessageService {
  public messages: string[] = [];

  constructor() { }

  add(message:string) {
    this.messages.push(message);

    setTimeout(() => {
      this.clear();
    }, 20000)
  }

  clear() {
    this.messages = [];
  }
}

即使已将MessageService注入到ErrorService构造函数中，也声明为未定义

0 个答案: