每个服务器响应+延迟后轮询服务器 [英] Polling server after each server response + delay

问题描述

我正在制作一个效果器，它将是轮询服务器.

I am working on an effect, that will be polling server.

我要实现的目标如下:

1)将GET请求发送到服务器

1) Send GET request to server

2)收到响应后，等待3秒钟

2) After response is received, wait 3 seconds

3)发送相同的GET请求

3) Send same GET request

4)收到响应后，等待3秒钟

4) After response is received, wait 3 seconds

5)发送相同的GET请求

5) Send same GET request

...等等.

我现在拥有的代码无法正常工作，因为它每3秒轮询一次服务器，无论是否收到响应:

The code that I have now, doesn't quite work, as it polls server every 3 seconds, no matter if response was received or not:

@Effect()
pollEntries$ = this.actions$.pipe(
  ofType(SubnetBrowserPageActions.SubnetBrowserPageActionTypes.StartPollingSubnetEntries),
  switchMap(() => {
    return timer(0, 3000);
  }),
  takeUntil(this.actions$.pipe(ofType(SubnetBrowserPageActions.SubnetBrowserPageActionTypes.StopPollingSubnetEntries))),
  switchMap(() => {
    return this.subnetBrowserService.getSubnetEntries();
  }),
  map((entries) => {
    return new SubnetBrowserApiActions.LoadEntriesSucces({ entries });
  }),
  catchError((error) => {
    return of(new SubnetBrowserApiActions.LoadEntriesFailure({ error }));
  }),
);

我正在努力解决的另一件事是如何停止轮询.如果我在请求发送到服务器之前发出StopPollingSubnetEntries动作，那么它可以正常工作-但是，如果我在请求发送之后发出它，那么我将在轮询停止之前再收到一个后续响应.

Another thing that I am struggling with is how to stop polling. If I emit StopPollingSubnetEntries action before request is sent to server, then it works fine - however if I emit it after request is sent, then I receive one more subsequent response, before polling stops.

推荐答案

您可以使用expand连续映射到下一个http请求并预先添加delay.

You could use expand to continuously map to the next http request and add a delay beforehand.

const stopPolling$ = this.actions$.pipe(
  ofType(SubnetBrowserPageActions.SubnetBrowserPageActionTypes.StopPollingSubnetEntries)
);

const httpRequest$ = this.subnetBrowserService.getSubnetEntries().pipe(
  map(entries => new SubnetBrowserApiActions.LoadEntriesSucces({ entries })),
  catchError(error => of(new SubnetBrowserApiActions.LoadEntriesFailure({ error })))
)

const pollEntries$ = this.httpRequest$.pipe(
  expand(_ => of(1).pipe(
    delay(3000),
    mergeMap(_ => this.httpRequest$),
  )),
  takeUntil(this.stopPolling$)
);

要开始轮询，您必须订阅pollEntries$.

To start polling you have to subscribe to pollEntries$.

startPolling() {
  this.pollEntries$.subscribe(entries => console.log(entries));
}

或者在您的操作发出时映射到pollEntries.

Or map to the pollEntries whenever your action emits.

const pollEntriesOnAction$ = this.actions$.pipe(
  ofType(SubnetBrowserPageActions.SubnetBrowserPageActionTypes.StartPollingSubnetEntries),
  switchMap(() => this.pollEntries$)
);

this.pollEntriesOnAction$.subscribe(entries => console.log(entries));

https://stackblitz.com/edit/angular-mu3kp5

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