CountDownTimer的用法及原理

1.主線程中使用

值得注意的是，CountDownTimer可以在主線程中直接使用。驗證一下回調的執行線程。在主線程中執行如下代碼

CountDownTimer countDownTimer = new CountDownTimer(1000L * 30, 1000L) {
            @Override
            public void onTick(long millisUntilFinished) {
                // your logic for tick
                Log.i("TEST", "onTick - " + Thread.currentThread() + ", id - " + Thread.currentThread().getId());
            }
 
            @Override
            public void onFinish() {
                // your logic for finish
 
                Log.i("TEST", "onFinish" + Thread.currentThread() + ", id - " + Thread.currentThread().getId());
            }
};
countDownTimer.start();

Log：

02-24 14:05:13.545 30358 30358 I TEST    : onTick - Thread[main,5,main], id - 1
02-24 14:05:14.546 30358 30358 I TEST    : onTick - Thread[main,5,main], id - 1
02-24 14:05:15.548 30358 30358 I TEST    : onTick - Thread[main,5,main], id - 1
02-24 14:05:16.550 30358 30358 I TEST    : onTick - Thread[main,5,main], id - 1
02-24 14:05:17.551 30358 30358 I TEST    : onTick - Thread[main,5,main], id - 1
02-24 14:05:18.553 30358 30358 I TEST    : onTick - Thread[main,5,main], id - 1
02-24 14:05:19.555 30358 30358 I TEST    : onTick - Thread[main,5,main], id - 1
02-24 14:05:20.557 30358 30358 I TEST    : onTick - Thread[main,5,main], id - 1
02-24 14:05:21.560 30358 30358 I TEST    : onTick - Thread[main,5,main], id - 1
02-24 14:05:22.563 30358 30358 I TEST    : onTick - Thread[main,5,main], id - 1
02-24 14:05:23.566 30358 30358 I TEST    : onTick - Thread[main,5,main], id - 1
02-24 14:05:24.569 30358 30358 I TEST    : onTick - Thread[main,5,main], id - 1
02-24 14:05:25.571 30358 30358 I TEST    : onTick - Thread[main,5,main], id - 1
02-24 14:05:26.573 30358 30358 I TEST    : onTick - Thread[main,5,main], id - 1
02-24 14:05:27.575 30358 30358 I TEST    : onTick - Thread[main,5,main], id - 1
02-24 14:05:28.578 30358 30358 I TEST    : onTick - Thread[main,5,main], id - 1
02-24 14:05:29.580 30358 30358 I TEST    : onTick - Thread[main,5,main], id - 1
02-24 14:05:30.581 30358 30358 I TEST    : onTick - Thread[main,5,main], id - 1
02-24 14:05:31.583 30358 30358 I TEST    : onTick - Thread[main,5,main], id - 1
02-24 14:05:32.586 30358 30358 I TEST    : onTick - Thread[main,5,main], id - 1
02-24 14:05:33.588 30358 30358 I TEST    : onTick - Thread[main,5,main], id - 1
02-24 14:05:34.589 30358 30358 I TEST    : onTick - Thread[main,5,main], id - 1
02-24 14:05:35.592 30358 30358 I TEST    : onTick - Thread[main,5,main], id - 1
02-24 14:05:36.595 30358 30358 I TEST    : onTick - Thread[main,5,main], id - 1
02-24 14:05:37.598 30358 30358 I TEST    : onTick - Thread[main,5,main], id - 1
02-24 14:05:38.599 30358 30358 I TEST    : onTick - Thread[main,5,main], id - 1
02-24 14:05:39.601 30358 30358 I TEST    : onTick - Thread[main,5,main], id - 1
02-24 14:05:40.602 30358 30358 I TEST    : onTick - Thread[main,5,main], id - 1
02-24 14:05:41.604 30358 30358 I TEST    : onTick - Thread[main,5,main], id - 1
02-24 14:05:43.546 30358 30358 I TEST    : onFinishThread[main,5,main], id - 1

可見，回調執行在主線程，這也就意味着可以在回調中直接處理UI，還是很方便的。

2.在工作線程中使用

不能在工作線程中像主線程一樣簡單使用的原因，是CountDownTimer是基於Handler的，細節將在原理部分說明。主線程已經由安卓框架層啟動了消息循環，所以可以直接使用。那么在工作線程中怎樣使用呢？可以借助於HanderThread。在onLooperPrepared()中初始化並開啟CountDownTimer：

new HandlerThread("TestThread") {
    protected void onLooperPrepared() {
        CountDownTimer countDownTimer = new CountDownTimer(1000L * 30, 1000L) {
            @Override
            public void onTick(long millisUntilFinished) {
                // your logic for tick
                Log.i("TEST", "onTick - " + Thread.currentThread() + ", id - " + Thread.currentThread().getId());
            }

            @Override
            public void onFinish() {
                // your logic for finish
                Log.i("TEST", "onFinish" + Thread.currentThread() + ", id - " + Thread.currentThread().getId());
            }
        };
        countDownTimer.start();
    }
}.start();

執行log如下：

02-24 14:03:35.789 30099 30222 I TEST    : onTick - Thread[TestThread,5,main], id - 473
02-24 14:03:36.790 30099 30222 I TEST    : onTick - Thread[TestThread,5,main], id - 473
02-24 14:03:37.793 30099 30222 I TEST    : onTick - Thread[TestThread,5,main], id - 473
02-24 14:03:38.795 30099 30222 I TEST    : onTick - Thread[TestThread,5,main], id - 473
02-24 14:03:39.797 30099 30222 I TEST    : onTick - Thread[TestThread,5,main], id - 473
02-24 14:03:40.800 30099 30222 I TEST    : onTick - Thread[TestThread,5,main], id - 473
02-24 14:03:41.801 30099 30222 I TEST    : onTick - Thread[TestThread,5,main], id - 473
02-24 14:03:42.803 30099 30222 I TEST    : onTick - Thread[TestThread,5,main], id - 473
02-24 14:03:43.804 30099 30222 I TEST    : onTick - Thread[TestThread,5,main], id - 473
02-24 14:03:44.806 30099 30222 I TEST    : onTick - Thread[TestThread,5,main], id - 473
02-24 14:03:45.809 30099 30222 I TEST    : onTick - Thread[TestThread,5,main], id - 473
02-24 14:03:46.810 30099 30222 I TEST    : onTick - Thread[TestThread,5,main], id - 473
02-24 14:03:47.813 30099 30222 I TEST    : onTick - Thread[TestThread,5,main], id - 473
02-24 14:03:48.814 30099 30222 I TEST    : onTick - Thread[TestThread,5,main], id - 473
02-24 14:03:49.816 30099 30222 I TEST    : onTick - Thread[TestThread,5,main], id - 473
02-24 14:03:50.818 30099 30222 I TEST    : onTick - Thread[TestThread,5,main], id - 473
02-24 14:03:51.820 30099 30222 I TEST    : onTick - Thread[TestThread,5,main], id - 473
02-24 14:03:52.821 30099 30222 I TEST    : onTick - Thread[TestThread,5,main], id - 473
02-24 14:03:53.823 30099 30222 I TEST    : onTick - Thread[TestThread,5,main], id - 473
02-24 14:03:54.825 30099 30222 I TEST    : onTick - Thread[TestThread,5,main], id - 473
02-24 14:03:55.827 30099 30222 I TEST    : onTick - Thread[TestThread,5,main], id - 473
02-24 14:03:56.828 30099 30222 I TEST    : onTick - Thread[TestThread,5,main], id - 473
02-24 14:03:57.829 30099 30222 I TEST    : onTick - Thread[TestThread,5,main], id - 473
02-24 14:03:58.831 30099 30222 I TEST    : onTick - Thread[TestThread,5,main], id - 473
02-24 14:03:59.832 30099 30222 I TEST    : onTick - Thread[TestThread,5,main], id - 473
02-24 14:04:00.835 30099 30222 I TEST    : onTick - Thread[TestThread,5,main], id - 473
02-24 14:04:01.836 30099 30222 I TEST    : onTick - Thread[TestThread,5,main], id - 473
02-24 14:04:02.838 30099 30222 I TEST    : onTick - Thread[TestThread,5,main], id - 473
02-24 14:04:03.840 30099 30222 I TEST    : onTick - Thread[TestThread,5,main], id - 473
02-24 14:04:05.791 30099 30222 I TEST    : onFinishThread[TestThread,5,main], id - 473