安卓验证码倒计时实现

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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