Android中再按一次退出提醒实现的两种方法

 long waitTime = 2000; 
 long touchTime = 0; 
 @Override
 public boolean onKeyDown(int keyCode, KeyEvent event) {
 if(event.getAction() == KeyEvent.ACTION_DOWN && KeyEvent.KEYCODE_BACK == keyCode) { 
     long currentTime = System.currentTimeMillis(); 
     if((currentTime-touchTime)>=waitTime) { 
     //让Toast的显示时间和等待时间相同
       Toast.makeText(this, "再按一次退出", (int)waitTime).show(); 
       touchTime = currentTime; 
     }else { 
       finish(); 
     } 
     return true; 
   } 
   return super.onKeyDown(keyCode, event); 
 }

 @Override
 public void onBackPressed() {
    long currentTime = System.currentTimeMillis(); 
    if((currentTime-touchTime)>=waitTime) { 
     //让Toast的显示时间和等待时间相同
      Toast.makeText(this, "再按一次退出", (int)waitTime).show(); 
      touchTime = currentTime; 
    }else { 
      finish(); 
    } 
 }