具有超时和检查 RxJs 可观察值轮询的递归函数 [英] Recursive function with timeout and check RxJs Observable value polling

问题描述

我有递归函数:repeatAlert，如果data.answered === null:

I have the recursive function: repeatAlert that is called again if data.answered === null:

....编辑

      this.repeatAlert(id).subscribe( val => console.log(val));
      console.log('1stCall Alert: ', new Date().getMinutes());

....

  find(id: number): Observable<any> {
        return this.http.get(`${this.resourceUrl}ByAlertId/${id}`
  }

  repeatAlert(id: number) {
    this.find(id).subscribe((data: AlertInt) => {
       if (data.answered === null ) {
          this.sendNotification('Alert ', data.text);
          console.log('Call Alert: ', new Date().getMinutes(), data.id);

          setTimeout(() => {
            if (data.answered === null) {
              this.repeatAlert(id);
            }
          }, data.repeating * 1000 * 60);
       }
    });
  }

当我改变数据库中data.answered的值时，我无法用这个可观察的find(id)读取data的变化.回答.所以它一直在调用 repeatAlert 永远......

When I change the value of data.answered in the database, I can't read with this observable find(id) the change of data.answered. So it keeps calling repeatAlert forever ...

我做错了什么?

额外问题:循环还是递归函数更好?

Extra question: Is it better a loop or recursive function ?

推荐答案

您正在进行投票.我建议如下:

You are doing polling. I suggest something like following:

find(id: number): Observable<any> {
  return this.http.get(`${this.resourceUrl}ByAlertId/${id}`;
}

repeatAlert(id: number) {
  // request data from the endpoint and execute necessary code
  const data$ = this.find(id).pipe(
    tap(data => {
      if (data.answered === null) {
        this.sendNotification('Alert ', data.text);
      }
    })
  );

  // polling will start if on the first try we don't have data.answered
  const startPolling = (duration: number) => timer(duration, duration).pipe(
    //take(10), // let's say we want to stop after 10 tries
    concatMap(() => data$),
    takeWhile(data => data.answered === null), // when to stop polling
  );

  // if data.answered is null on the first try switch to polling otherwise end
  return data$.pipe(
    switchMap(data => data.answered === null ?
      startPolling(data.repeating * 1000 * 60) :
      of(data)
    ),
  );
}

另请注意，我更改了您的repeatAlert，最好从方法返回 Observable 并自己订阅以避免内存泄漏.您应该自己订阅和取消订阅.另外，我建议您使用 take(10) 为例，以便轮询不会无限期地继续，这取决于您.

Also note that I changed your repeatAlert, it's better to return Observable from the method and subscribe yourself to avoid memory leaks. You should subscribe and unsubscribe yourself. Also, I suggest you to use take(10) for example so that polling doesn't continue indefinitely, it's up to you.

timer(dueTime, period) 的工作原理如下: 它会在 dueTime 之后发出第一个事件，并在每个 之后继续发出事件期间.

timer(dueTime, period) works like this: It will emit first event after dueTime and continue emitting events after every period.

编辑 takeWhile 条件为真而非条件为假

Edit takeWhile condition is true and not condition is false

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