用kotlin的写法写一个 CountDownTimer

好的，以下是用Kotlin写一个CountDownTimer的示例代码：

class MyCountDownTimer(val millisInFuture: Long, val countDownInterval: Long) {
    private var isTimerRunning = false
    private var timeLeft: Long = millisInFuture
    private var timer: CountDownTimer? = null
    private var onTickListener: ((Long) -> Unit)? = null
    private var onFinishListener: (() -> Unit)? = null

    fun start() {
        if (!isTimerRunning) {
            timer = object : CountDownTimer(timeLeft, countDownInterval) {
                override fun onTick(millisUntilFinished: Long) {
                    timeLeft = millisUntilFinished
                    onTickListener?.invoke(millisUntilFinished)
                }

                override fun onFinish() {
                    isTimerRunning = false
                    onFinishListener?.invoke()
                }
            }.start()
            isTimerRunning = true
        }
    }

    fun cancel() {
        timer?.cancel()
        isTimerRunning = false
    }

    fun setTimeLeft(timeLeft: Long) {
        this.timeLeft = timeLeft
    }

    fun setOnTickListener(onTickListener: (Long) -> Unit) {
        this.onTickListener = onTickListener
    }

    fun setOnFinishListener(onFinishListener: () -> Unit) {
        this.onFinishListener = onFinishListener
    }
}

使用方法如下：

val myCountDownTimer = MyCountDownTimer(60000, 1000)

myCountDownTimer.setOnTickListener { millisUntilFinished ->
    // Update UI with time left
}

myCountDownTimer.setOnFinishListener {
    // Do something when timer finishes
}

myCountDownTimer.start()

这个CountDownTimer会持续60秒，并且每隔1秒回调一次onTickListener，最后结束时调用onFinishListener。如果需要修改时间，可以调用setTimeLeft方法。如果需要停止计时器，可以调用cancel方法。