当标志变为真时开始轮询

Question

我想在atrribute的值变为真时开始轮询，有没有什么方法可以在flag变为真时开始轮询，目前我的实现是：

 ngOnInit(){
        //want to start when startedPoll becomes true otherwise dont
        let url = 'getStatus'
        this.pollingSubscribe = interval(5000).pipe(
          switchMap(() => this.http.getCall(url))
        ).subscribe(data => {
          if(data['success']) {
            this.pollingData =data['result']

            this.processData(this.pollingData)
          }

        }, error =>{
          this.error = true;
          this.errorData = this.createPollingFiles;
        })
      }

startPoll(){
  this.startedPoll = true;
}

当startedPoll变为true时开始轮询数据，请不要提示if 和 else 实施

Answer 1

如果 startedPoll 变成 true 的唯一方法是调用 startPoll 方法，那么只需将 subscribe 调用从 ngOnInit方法进入 startPoll:

ngOnInit() {
    // want to start when startedPoll becomes true otherwise dont
    let url = 'getStatus'
    this.pollingObservable = interval(5000).pipe(
        switchMap(() => this.http.getCall(url))
    );
}

startPoll() {
    this.pollingSubscribe = this.pollingObservable.subscribe(data => {
        if (data['success']) {
            this.pollingData = data['result']
            this.processData(this.pollingData)
        }
    }, error => {
        this.error = true;
        this.errorData = this.createPollingFiles;
    })
    this.startedPoll = true;
}

ngOnDestroy() {
    if (this.pollingSubscribe) {
        this.pollingSubscribe.unsubscribe();
    }
}

确保在轮询活动时 startPoll 不会被调用超过一次。 否则，Subscription 已经存储在 this.pollingSubscribe会丢失，轮询频率会翻倍，部分轮询会在组件销毁后继续。

当标志变为真时开始轮询

Start polling when flag becomes true

observable

angular

rxjs6