使用 flow 实现倒计时

Android 倒计时一般方式：

• Handler 方式
• CountDownTimer 方式
• RxJava 方式

上述倒计时方式实现省略，这里使用 kotlin 的 flow 实现：

fun countDownCoroutines(
    total: Int,
    scope: CoroutineScope,
    onTick: (Int) -> Unit,
    onStart: (() -> Unit)? = null,
    onFinish: (() -> Unit)? = null,
): Job {
    return flow {
        for (i in total downTo 0) {
            emit(i)
            delay(1000)
        }
    }.flowOn(Dispatchers.Main)
        .onStart { onStart?.invoke() }
        .onCompletion { onFinish?.invoke() }
        .onEach { onTick.invoke(it) }
        .launchIn(scope)
}

使用：

private var mCountdownJob: Job? = null
mBinding.btnStart.setOnClickListener {
    mCountdownJob = countDownCoroutines(60, lifecycleScope,
        onTick = { second ->
            mBinding.text.text = "${second}s后重发"
        }, onStart = {
            // countdown start
        }, onFinish = {
            // countdown finished, reset state
            mBinding.text.text = "发送验证码"
        })
}
mBinding.btnStop.setOnClickListener { 
    // cancel countdown
    mCountdownJob?.cancel() 
}