获取验证码的时候经常用到一个控件，就是点击按钮之后会出现60秒倒计时。
其实这个原理很简单，就是 textview 和 Timer 的混合使用

直接贴代码

  public class VerificationCountDownTimer extends CountDownTimer { 
    private final String text; 
    private final TextView view;    
    private  final  static  long MILLIS_IN_FUTURE=60000;//默认60秒 
    private  final  static  long COUNT_DOWN_INTERVAL=1000;//1秒计时一次   
   /**     * @param millisInFuture    The number of millis in the future from the call     *                          to {@link #start()} until the countdown is done and {@link #onFinish()}     *                          is called.     * @param countDownInterval The interval along the way to receive     *                          {@link #onTick(long)} callbacks.     */   
    public VerificationCountDownTimer(long millisInFuture, long countDownInterval , TextView textView) {//        super(countDownInterval, millisInFuture);        super(MILLIS_IN_FUTURE, COUNT_DOWN_INTERVAL);   
           this.view = textView;      
           text = textView.getText().toString();   
   }  
    @Override  
    public void onFinish() {// 计时完毕    
      view.setText(text);   
       view.setClickable(true);  
    } 
     @Override  
     public void onTick(long millisUntilFinished) {     
           view.setClickable(false);// 防止重复点击   
           view.setText(millisUntilFinished / COUNT_DOWN_INTERVAL + "秒后可点击");   
 }
}

使用时 只需要

     verificationCountDown =  (TextView)findViewById(R.id.verificationCountDown);
     verificationCountDown.setOnClickListener(new View.OnClickListener() {   
     @Override    public void onClick(View v) { //0,0 可以自定义
      new VerificationCountDownTimer(0,0,verificationCountDown); 
   }
});

是不是很简单，那么我们来看看 CountDownTimer源码

public synchronized final CountDownTimer start() {  
mCancelled = false;    
if (mMillisInFuture <= 0) {   
     onFinish(); 
     return this;    
}   
  // SystemClock.elapsedRealtime() 返回系统启动到现在的时间
 mStopTimeInFuture = SystemClock.elapsedRealtime() +   mMillisInFuture;  
 mHandler.sendMessage(mHandler.obtainMessage(MSG));  
//发送消息 
 return this;

}

在仔细看一下消息处理

 private Handler mHandler = new Handler() {   
 @Override
 public void handleMessage(Message msg) {   
     synchronized (CountDownTimer.this) {   
  //如果取消事件    
     if (mCancelled) {             
           return;           
     }         
  // 计算倒数时间 持续的
     final long millisLeft = mStopTimeInFuture - SystemClock.elapsedRealtime();  
    //到0时，自动调用finish 方法
          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);   
         }     
     } 
   }
};