如何在另一个服务中使用 AlertService（用于显示错误消息的小吃栏）？

Question

我正在尝试订阅服务内的可观察对象。但是，我需要用于AlertService显示错误。一个服务包含另一个服务（循环依赖？）。

这是警报服务

@Injectable()
export class AlertService {
  private subject = new Subject<any>();
  private keepAfterNavigationChange = false;

  constructor(private router: Router) {
    // clear alert message on route change
    router.events.subscribe(event => {
      if (event instanceof NavigationStart) {
        if (this.keepAfterNavigationChange) {
          // only keep for a single location change
          this.keepAfterNavigationChange = false;
        } else {
          // clear alert
          this.subject.next();
        }
      }
    });
  }

  success(message: string, keepAfterNavigationChange = false) {
    this.keepAfterNavigationChange = keepAfterNavigationChange;
    this.subject.next({ type: 'success', text: message });
  }

  error(message: string, keepAfterNavigationChange = false) {
    this.keepAfterNavigationChange = keepAfterNavigationChange;
    this.subject.next({ type: 'error', text: message });
  }

  getMessage(): Observable<any> {
    return this.subject.asObservable();
  }
}

AlertService 成为了一个Mat Snackbaron AlertComponent. 我正在另一个组件上渲染这个小吃栏。

export class AlertComponent implements OnInit {
  message: any;

  constructor(private alertService: AlertService, public snackBar: MatSnackBar) { }

  ngOnInit() {
    // trigger Snackbar after AlertService is called
    this.alertService.getMessage().subscribe(message => {
      if (message != null) {
        // there is a message to show, so change snackbar style to match the message type
        if (message.type === 'error') {
          this.snackBar.open(message.text, undefined, { duration: 8000, verticalPosition: 'bottom', panelClass: ['snackbar-error'] });
        } else if (message.type === 'success') {
          this.snackBar.open(message.text, undefined, { duration: 8000, verticalPosition: 'bottom', panelClass: ['snackbar-success'] });
        } else {
          this.snackBar.open(message.text, undefined, { duration: 8000, verticalPosition: 'bottom' });
        }
      }
    });
  }

}

我可以像这样订阅内部组件：

export class AboutComponent implements OnInit {
  
  ngOnInit() {
    this.emailService.sendEmail('example@gmail.com')
      .subscribe(code => {
          console.log(code);
          this.alertService.success('Thanks for your message!');
      }, error => {
        this.alertService.error('Error sending message.');
      }
    );
  }
      
}

@Injectable()
export class EmailService {

    constructor(private http: HttpClient) { }

    sendEmail(email: Email) {
        return this.http.post(BACKEND_URL + 'send', email);
    }
}

然而，我正在尝试订阅内部服务，因为EmailService将在多个组件中使用。我怎样才能实现这种行为？

Answer 1

您的服务可以注入其他服务中

@Injectable()export class EmailService {

constructor(private http: HttpClient, private alertService: AlertService) { }

sendEmail(email: Email) {
    return this.http.post(BACKEND_URL + 'send', email).map( result => this.alertService.alert(result););


  }
}

如果AlertService使用EmailService并且EmailService使用AlertService，那就是循环了