Angular2, unsubsribe from event in ngOnDestroy [duplicate]

问题

In my application I have some components that communicate by means of EventService.

@Injectable()
export class EventService {
  public myEvent: EventEmitter<any> = new EventEmitter();
  constructor() {}
}

This service is injected in a EmitterComponent that emits the event when a button is clicked

@Component({
  selector: 'emitter',
  template: `<button (click)="onClick()">Click me</button>`,
})
export class EmitterComponent {
  constructor(private eventService:EventService) {}
  onClick() {
    this.eventService.myEvent.emit();
  }
}

and in a ReceiverComponent that subscribes to the event and for each event received increments a counter

@Component({
  selector: 'receiver',
  template: `Count: {{count}}`,
})
export class ReceiverComponent {
  public count = 0;
  constructor(private eventService:EventService) {
    this.eventService.myEvent.subscribe(() => this.count++;);
  }
}

The application has multiple views (in this example just two): PageA and PageB. EmitterComponent and ReceiverComponent are in PageA. Every time I go to PageB and come back to PageA, a new ReceiverComponent is created and when I click the button in EmitterComponent, the event callback function of ReceiverComponent is executed several times.

To avoid this I unsubscribe ReceiverComponent from myEvent in ngOnDestroy

ngOnDestroy() {
  this.eventService.myEvent.unsubscribe();
}

but this causes the following Exception

EXCEPTION: Error during instantiation of ReceiverComponent!.
ORIGINAL EXCEPTION: Error: Cannot subscribe to a disposed Subject

How can I avoid that? How to unsubscribe correctly?

For a better understanding I've created this plunker where you can see the error and some comments in the console.

回答1:

You get a subscription from .subscribe(). Use its unsubscribe() method to cancel the subscription.

@Component({
  selector: 'receiver',
  template: `Count: {{count}}`,
})
export class ReceiverComponent {
  public count = 0;
  private subscription;
  constructor(private eventService:EventService) {
    this.subscription = this.eventService.myEvent.subscribe(() => this.count++;);
  }
  ngOnDestroy() {
    this.subscription.unsubscribe();
  }
}

回答2:

I think your should cancel the subscription, as described below:

export class ReceiverComponent {
  public count = 0;
  private id;

  constructor(private eventService:EventService) {
    this.id = Date.now();
    console.log("ReceiverComponent constructor " + this.id);
    this.subscription = this.eventService.myEvent.subscribe(() => {
      console.log("count " + this.count + " (id ReceiverComponent instance: " + this.id + ")");
      this.count++;
    });
  }

  ngOnDestroy() {
    console.log("onDestroy of ReceiverComponent " + this.id)
    //this cause "Cannot subscribe to a disposed Subject."
    //this.eventService.myEvent.unsubscribe();
    this.subscription.unsubscribe();
  }
}

In fact, EventEmitters are shared observables, i.e. hot observables. Here is a link that could interest you: https://github.com/Reactive-Extensions/RxJS/blob/master/doc/gettingstarted/creating.md.

Hope it helps you, Thierry

来源：https://stackoverflow.com/questions/34926628/angular2-unsubsribe-from-event-in-ngondestroy

标签

angular

eventemitter