Rx flatMapLatest doesn't pass completed through? - system.reactive

Question

I expected to see timer -> Event completed get outputted right after I saw running -> Event completed but it didn't happen.
Can someone explain why and give me some idea on how to complete the timer observable?
/// playground
import RxSwift
import PlaygroundSupport
PlaygroundPage.current.needsIndefiniteExecution = true
struct TimerCountdown {
let timer: Observable<Int>
init(running: Observable<Bool>) {
timer = running.flatMapLatest { $0 ? Observable<Int>.interval(1.0, scheduler: MainScheduler.instance) : Observable<Int>.never() }
}
}
let running = PublishSubject<Bool>()
let countdown = TimerCountdown(running: running)
_ = running.debug("running").subscribe()
_ = countdown.timer.debug("timer").subscribe()
running.onNext(true)
DispatchQueue.main.asyncAfter(deadline: .now() + 3.5) {
running.onNext(false)
}
DispatchQueue.main.asyncAfter(deadline: .now() + 7.5) {
running.onNext(true)
}
DispatchQueue.main.asyncAfter(deadline: .now() + 10.5) {
running.onCompleted()
}

Answer 1

This is the solution I found:
struct TimerCountdown {
let timer: Observable<Int>
init(running: Observable<Bool>) {
timer = running
.flatMapLatest { $0 ? Observable<Int>.interval(1.0, scheduler: MainScheduler.instance) : Observable<Int>.never() }
.takeUntil(running.materialize().filter { $0.isCompleted })
}
}
Here's another answer that doesn't require subscribing to running twice:
struct TimerCountdown {
let timer: Observable<Int>
init(running: Observable<Bool>) {
timer = running.materialize()
.flatMapLatest { (event) -> Observable<Int> in
switch event {
case let .next(value):
return value ? Observable<Int>.interval(1.0, scheduler: MainScheduler.instance) : Observable.never()
case .completed:
return Observable.empty()
case let .error(error):
return Observable.error(error)
}
}
}
}