怎么在Android应用中利用View实现一个倒计时功能

 public class CountDownView extends TextView {      private long totalMills = 10 * 1000;//倒计时的总时间，根据需要更改这个值   private long interval = 1000;//倒计时的时间间隔      public CountDownView(Context context) {     super(context);   }    public CountDownView(Context context, AttributeSet attrs) {     super(context, attrs);   }    public CountDownView(Context context, AttributeSet attrs, int defStyle) {     super(context, attrs, defStyle);   }    private TimeCount mTimeCount;      private void startCount(long totalMills, long countDownInterval) {     if (mTimeCount == null)       mTimeCount = new TimeCount(totalMills, countDownInterval);     mTimeCount.start();   }      public void start(){     defaultText = getText().toString();     startCount(totalMills, interval);   }    public void cancel() {     if (mTimeCount != null){       mTimeCount.onFinish();       mTimeCount.cancel();     }   }    String defaultText = "";//获取到在点击之前的文本内容    class TimeCount extends CountDownTimer {      public TimeCount(long millisInFuture, long countDownInterval) {       super(millisInFuture, countDownInterval);     }      @Override     public void onTick(long millisUntilFinished) {       setEnabled(false);       setText(millisUntilFinished / 1000 + "S");     }      @Override     public void onFinish() {       setEnabled(true);       setText(defaultText);     }    }  }