怎么在Android中实现一个倒计时功能

  private int minute = 30;//这是分钟
  private int second = 0;//这是分钟后面的秒数。这里是以30分钟为例的，所以，minute是30，second是0
  private TextView timeView;
  private Timer timer;
  private TimerTask timerTask;
  //这是接收回来处理的消息
  private Handler handler = new Handler() {
    public void handleMessage(Message msg) {
      if (minute == 0) {
        if (second == 0) {
          timeView.setText("Time out !");
          if (timer != null) {
            timer.cancel();
            timer = null;
          }
          if (timerTask != null) {
            timerTask = null;
          }
        } else {
          second--;
          if (second >= 10) {
            timeView.setText("0" + minute + ":" + second);
          } else {
            timeView.setText("0" + minute + ":0" + second);
          }
        }
      } else {
        if (second == 0) {
          second = 59;
          minute--;
          if (minute >= 10) {
            timeView.setText(minute + ":" + second);
          } else {
            timeView.setText("0" + minute + ":" + second);
          }
        } else {
          second--;
          if (second >= 10) {
            if (minute >= 10) {
              timeView.setText(minute + ":" + second);
            } else {
              timeView.setText("0" + minute + ":" + second);
            }
          } else {
            if (minute >= 10) {
              timeView.setText(minute + ":0" + second);
            } else {
              timeView.setText("0" + minute + ":0" + second);
            }
          }
        }
      }
    }

  };


  @Override
  protected void onCreate(Bundle savedInstanceState) {
    requestWindowFeature(Window.FEATURE_NO_TITLE);
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    timeView = (TextView) findViewById(R.id.tv);

    timeView.setText(minute + ":" + second);

    timerTask = new TimerTask() {

      @Override
      public void run() {
        Message msg = new Message();
        msg.what = 0;
        handler.sendMessage(msg);
      }
    };

    timer = new Timer();
    timer.schedule(timerTask, 0, 1000);

  }

  @Override
  protected void onDestroy() {
    if (timer != null) {
      timer.cancel();
      timer = null;
    }
    if (timerTask != null) {
      timerTask = null;
    }
    minute = -1;
    second = -1;
    super.onDestroy();
  }

  @Override
  protected void onStart() {
    super.onStart();
  }

  @Override
  protected void onStop() {
    super.onStop();
  }

  @Override
  protected void onResume() {
    super.onResume();
  }

  @Override
  protected void onRestart() {
    super.onRestart();
  }

  @Override
  protected void onPause() {
    super.onPause();
  }
}