RxJs/NgRx-是否有一种方法可以“取消"邮件.延迟运算符之后的流 [英] RxJs/NgRx - is there a way to "Cancel" a stream after the delay operator

问题描述

我正在使用NgRx在Angular应用程序中使用轮询方案.

I am using a polling scheme in my Angular application using NgRx.

为简化起见，我有类似以下内容的内容...

To simplify things, I have something like the following...

    public stopPolling$ = createEffect(() => this.actions$.pipe(
        ofType(actions.stopPolling),
        tap(_ => this.isPollingActive = false),    
        map(_ => actions.stopPolling())
      ), { dispatch: false });

     public continuePolling$ = createEffect(() => this.actions$.pipe(
        ofType(actions.getData),
        tap(_ => this.logger.debug('continue polling')),    
        delay(8000),    
        switchMap(_ => this.pollData())
      ), { dispatch: false });


    private pollData() {
       if (!this.isPollingActive)
         return;
    }

在我的"StopPolling"中，我设置了一个标志，但是如果我在delay(8000)中时将其重新启动(即isPollingActive等回到true)，则延迟将消失并且最终将调用getData多次.

In my "StopPolling" I set a flag, but if it is restarted (ie isPollingActive is et back to true) while I am in the delay(8000), the delay will exit and I will end up with the getData being called multiple times.

所以，我的问题是，是否有办法在延迟后逐步调用switchMap(_ => this.pollData())，即是否有办法在超时时间之前强制延迟退出"?

So, my question is, is there a way to step the switchMap(_ => this.pollData()) being called after the delay - ie is there someway to "force the delay to exit" before the timeout period?

几乎(如果您知道C#/.net).就像manualResetEvent.WaitOne(8000)一样，可以通过在manualResetEvent对象上调用Set()来取消.

Almost (if you know C#/.net). like a manualResetEvent.WaitOne(8000) which can be cancelled by calling Set() on the manualResetEvent object.

我希望我已经清楚地描述了吗?

I hope I have described this clearly?

预先感谢

推荐答案

您可以使用timer创建一个延迟后发出的可观察对象，并使用takeUntil取消订阅以提早退出:

You can create an observable that emits after a delay using timer and unsubscribe with takeUntil to exit early:

this.actions$.pipe(
  ofType(actions.getData),
  tap(_ => this.logger.debug('continue polling')),   
  switchMap(_ =>
    timer(8000).pipe(
      takeUntil(this.actions$.pipe(ofType(actions.stopPolling))),
      concatMap(() => this.pollData())
    )
)

这还可以使您消除副作用this.isPollingActive = false并确保控制流保持在可观察范围之内.

This might also allow you to remove the side-effect this.isPollingActive = false and ensure that the control flow remains within the observable.

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