Android 使用flow实现倒计时的方式

    api 'org.jetbrains.Kotlinx:kotlinx-coroutines-core:1.4.2'
    api 'org.jetbrains.kotlinx:kotlinx-coroutines-android:1.4.1'
    // lifecycleScope(可选)
    api "androidx.lifecycle:lifecycle-runtime-ktx:2.2.0"

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)
}

private var mCountdownJob: Job? = null

mBinding.btnStart.setOnClickListener {
    mCountdownJob = countDownCoroutines(60, lifecycleScope,
        onTick = { second ->
            mBinding.text.text = "${second}s后重发"
        }, onStart = {
            // 倒计时开始
        }, onFinish = {
            // 倒计时结束，重置状态
            mBinding.text.text = "发送验证码"
        })
}
mBinding.btnStop.setOnClickListener { 
    // 取消倒计时
    mCountdownJob?.cancel() 

  
    public void startTimer() {
        if (timer == null) {
            timer = new Timer();
        }
        if (timerTask == null) {
            timerTask = new TimerTask() {
                @Override
                public void run() {
                    Message message = new Message();
                    message.what = 2;
                    handler.sendMessage(message);
                }
            };
        }
        if (timer != null && timerTask != null) {
            timer.schedule(timerTask, 0, 2000);
        }
    }
    
    public void stopTimer() {
        if (timer != null) {
            timer.cancel();
            timer = null;
        }
        if (timerTask != null) {
            timerTask.cancel();
            timerTask = null;
        }
    }

  private void countDown() {
        mdDisposable = Flowable.intervalRange(0, Constant.COUNT_DOWN, 0,                     1,TimeUnit.SECONDS)
                .observeOn(AndroidSchedulers.mainThread())
                .doOnNext((aLong) -> LogUtils.e("倒计时--" + aLong))
                .doOnComplete(() -> randomSelectSeat())
                .subscribe();
    }
    
     @Override
    protected void onDestroy() {
        if (mdDisposable != null) {
            mdDisposable.dispose();
        }
        super.onDestroy();
    }

//倒计时CountDownTimer
//每过1000毫秒执行一次onTick
//倒计时完成执行onFinish
CountDownTimer timer = new CountDownTimer(5000, 1000){
    @Override
    public void onTick(long sin) {
        Toast.makeText(MainActivity.this, "" + sin/1000, Toast.LENGTH_SHORT).show();
    }
 
    @Override
    public void onFinish() {
        Toast.makeText(MainActivity.this, "倒计时完成", Toast.LENGTH_SHORT).show();
    }
};
//开始
timer.start();
//暂停
if (timer != null) {
     timer.cancel();
     timer = null;
 }