Countdown can be said to be a common requirement of Android development, the previous implementation is generally the following schemes

  • The handler + postDelayed () method
  • The Timer + TimerTask + Handler mode is used
  • ScheduledExecutorService + Handler mode
  • RxJava way
  • CountDownTimer way

Now, with coroutines and Flow, we can use the Flow tool to implement this requirement more elegantly.

  1. Rely on the import
    api 'org. Jetbrains. Kotlinx: kotlinx coroutines -- core: 1.4.2'
    api 'org. Jetbrains. Kotlinx: kotlinx coroutines - android: 1.4.1'
    // lifecycleScope(optional)
    api "Androidx. Lifecycle: lifecycle - runtime - KTX: 2.2.0." "
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  1. Code implementation
 fun countDownCoroutines(total:Int,onTick:(Int) - >Unit,onFinish:()->Unit,
                        scope: CoroutineScope = GlobalScope):Job{
    return flow{
        for (i in total downTo 0){
            emit(i)
            delay(1000)
        }
    }.flowOn(Dispatchers.Default)
        .onCompletion { onFinish.invoke() }
        .onEach { onTick.invoke(it) }
        .flowOn(Dispatchers.Main)
        .launchIn(scope)
}
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The CoroutineScope uses GlobalScope by default. Considering memory leaks, lifecycleScope is recommended to better realize lifecycle management and avoid memory leaks.

The Demo address