倒计时功能可以是用[http://developer.android.com/reference/android/os/CountDownTimer.html CountDownTimer]

{{{
 new CountDownTimer(30000, 1000) {

     public void onTick(long millisUntilFinished) {
         mTextField.setText("seconds remaining: " + millisUntilFinished / 1000);
     }

     public void onFinish() {
         mTextField.setText("done!");
     }
  }.start();
}}}

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