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();

  }

}