android 连按两次退出程序

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 private long exitTime = 0;

 /**
  * 捕捉返回事件按钮
  *
  * 因为此 Activity 继承 TabActivity 用 onKeyDown 无响应，所以改用 dispatchKeyEvent
  * 一般的 Activity 用 onKeyDown 就可以了
  */

 @Override
 public boolean dispatchKeyEvent(KeyEvent event) {
   if (event.getKeyCode() == KeyEvent.KEYCODE_BACK) {
     if (event.getAction() == KeyEvent.ACTION_DOWN && event.getRepeatCount() == 0) {
       this.exitApp();
     }
     return true;
   }
   return super.dispatchKeyEvent(event);
 }

 /**
  * 退出程序
  */
 private void exitApp() {
   // 判断2次点击事件时间
   if ((System.currentTimeMillis() - exitTime) > 2000) {
     Toast.makeText(MainActivity.this, "再按一次退出程序", Toast.LENGTH_SHORT).show();
     exitTime = System.currentTimeMillis();
   } else {
     finish();
   }
 }