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安卓为验证码倒计时提供了一个很方便的类android.os.CountDownTimer
其使用方法：
new CountDownTimer(30000, 1000) { public void onTick(long millisUntilFinished) { mTextField.setText("seconds remaining: " + millisUntilFinished / 1000); } public void onFinish() { mTextField.setText("done!"); } }.start();
onTick 间隔时间回调 onfinish 倒计时完回调
从源码可以看到其实现主要是通过sendMessageDelayed实现的,其主要的逻辑如下：
private Handler mHandler = new Handler() { @Override public void handleMessage(Message msg) { synchronized (CountDownTimer.this) { if (mCancelled) { return; } final long millisLeft = mStopTimeInFuture - SystemClock.elapsedRealtime(); if (millisLeft <= 0) { onFinish(); } else if (millisLeft < mCountdownInterval) { // no tick, just delay until done sendMessageDelayed(obtainMessage(MSG), millisLeft); } else { long lastTickStart = SystemClock.elapsedRealtime(); onTick(millisLeft); // take into account user‘s onTick taking time to execute long delay = lastTickStart + mCountdownInterval - SystemClock.elapsedRealtime(); // special case: user‘s onTick took more than interval to // complete, skip to next interval while (delay < 0) delay += mCountdownInterval; sendMessageDelayed(obtainMessage(MSG), delay); } } } };
可以在以后做一些定时操作的时候，做相关的逻辑。
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原文地址：http://www.cnblogs.com/zhangzcf/p/5415741.html
