How to detect if a observable has not emitted any events for specific time in RxSwift

问题

I am trying to detect if a observable(my case button.rx.tap) has not emitted any value for say like 3 seconds. If yes, I would like to update the user interface. Here is my attempt so far:

Observable<Int>.interval(3, scheduler: MainScheduler.instance)
    .takeUntil(button.rx.tap) // I know take until will stop the timer sequence 
    .subscribe({ event in
        print(event)
        UIView.animate(withDuration: 0.4, animations: {
            if let number = event.element {
                let scale: CGFloat = number % 2 == 0 ? 1.5 : 1.0
                self.button.transform = CGAffineTransform(scaleX: scale, y: scale)
            }
        })
    })
    .addDisposableTo(disposeBag)

My goal is to animate the view whenever the button is not tapped for three seconds. I have tried scan, distinctUntilChanged and debounce but most combining operators I have encountered will emit items only when an item is emitted by a observable. Any help is much appreciated.

回答1:

enum Event {
case tap
case timeout
}

let tapOrTimeout = button.rx.tap
  .map { _ in Event.tap }
  .timeout(3, scheduler: MainScheduler.instance)
  .catchErrorJustReturn(.timeout)

Observable.repeatElement(tapOrTimeout).concat()
  .subscribe(onNext: { event in
    switch event {
    case .tap: tapHandler()
    case .timeout: callForAttention()
    }
  })

• timeout(_:scheduler:) will raise an error if no event comes out of the chain within 3 seconds.
• catchErrorJustReturn(_:) will transform the error into a .timeout event
• at this point, if the observable times out, it will also complete, hence nothing will happen afterward. Using Observable.repeatElement(_:).concat() we first create an Observable<Observable<Event>> and then concatenate inner observables. Which in our case means that we'll subscribe to the first, and the resubscribe to the same observable if the first completes.

---

If we had prefer to only play the callForAttention() animation once, we could have done the following

let tap = button.rx.tap
  .map { _ in Event.tap }

let tapOrTimeout = tap  
  .timeout(3, scheduler: MainScheduler.instance)
  .catchErrorJustReturn(.timeout)

Observable.of(tapOrTimeout, tap).concat()
  .subscribe(onNext: { /* same as above */})

This way, we first timeout, but then only emit an event when a tap occurs.

来源：https://stackoverflow.com/questions/42145623/how-to-detect-if-a-observable-has-not-emitted-any-events-for-specific-time-in-rx