angular - 如何订阅一次事件发射器？

Question

// Part of service
public someEvent: EventEmitter<number> = new EventEmitter();

....

// Component
@Component({
  selector: 'some-component',
  template: `...`
})
export class SomeComponent {
  constructor(public service: Service) {
    this.service.someEvent.subscribe((x) => {
      // Do something
    });
  }
}

SomeComponent 显示在 / 路由中。当我导航到我的应用程序中的不同路由并再次返回时，SomeComponent 将再次订阅该事件，导致回调触发两次。如何订阅一次事件或在销毁组件时取消订阅并再次订阅？

// Can't subscribe after.
ngOnDestroy() {
  this.service.someEvent.unsubscribe();
}

Answer 1

调用 subscribe 返回 instance of Disposable ，它有一个方法 dispose .

或者，如果您使用的是 RxJS 5，dispose has been renamed to unsubscribe (感谢@EricMartinez)。

并且来自 RxJS docs :

...when we're no longer interested in receiving the data as it comes streaming in, we call dispose on our subscription.

---

存储调用 subscribe 的结果，稍后在 ngOnDestroy 中处理订阅。

RxJS 5:

export class SomeComponent implements OnDestroy {
  constructor(public service: Service) {
    this.subscription = this.service.someEvent.subscribe((x) => {...});
  }
  ngOnDestroy() {
      this.subscription.unsubscribe();
  }
}

RxJS <5:

export class SomeComponent implements OnDestroy {
  constructor(public service: Service) {
    this.subscription = this.service.someEvent.subscribe((x) => {...});
  }
  ngOnDestroy() {
      this.subscription.dispose();
  }
}