RxSwift: Repeat a (completed) stream

Question

Assume I have a button which can be used to start and stop (toggle) an action.

let toggleStream: Observable<Bool> = toggleBtn.rx.tap.scan(false) { state, _ in !state }

I have another stream, that emits Integers continuously.

let emitter = Observable<Int>.interval(2.0, scheduler: timerScheduler)

Now I want to use the toggle stream to start and stop the emitting of the second stream. This is my approach:

Observable.combineLatest(toggleStream, emitter) { shouldEmit, evt in
    return (shouldEmit, evt)
}.takeWhile{ (shouldEmit, evt:Int) in
    return shouldEmit == true
}.map {(_, evt) in
    return evt
}

This works great for the first time. I can press the button and the Observable starts emitting its Ints. Also stopping works. Sadly I can't start it for a second time, because the stream is completed. How can I restart/retry/repeat it when the user toggles the button again?

Answer 1

Here's how I did it in the playground. You should be able to extrapolate:

//: Playground - noun: a place where people can play

import RxSwift

let toggleButton = PublishSubject<Void>()
let toggleStream: Observable<Bool> = toggleButton
    .scan(false) { state, _ in !state }
    .debug()
    .shareReplayLatestWhileConnected()

let emit = toggleStream
    .filter { $0 }
    .flatMapLatest { _ in
        Observable<Int>.interval(2.0, scheduler: MainScheduler.instance)
            .takeUntil(toggleStream.filter { !$0 })
    }


_ = emit.subscribe( {
    print($0)
})

toggleButton.onNext()
DispatchQueue.main.asyncAfter(deadline: DispatchTime.now() + 5.0) {
    toggleButton.onNext()
}
DispatchQueue.main.asyncAfter(deadline: DispatchTime.now() + 11.0) {
    toggleButton.onNext()
}
DispatchQueue.main.asyncAfter(deadline: DispatchTime.now() + 17.0) {
    toggleButton.onNext()
}

import PlaygroundSupport
PlaygroundPage.current.needsIndefiniteExecution = true