/**

 * 菜单、返回键响应

 */

@Override

public boolean onKeyDown(int keyCode, KeyEvent event) {

    // TODO Auto-generated method stub

    if(keyCode == KeyEvent.KEYCODE_BACK)

       {

           exitBy2Click();      //调用双击退出函数

       }

    return false;

}

/**

 * 双击退出函数

 */

private static Boolean isExit = false;

private void exitBy2Click() {

    Timer tExit = null;

    if (isExit == false) {

        isExit = true; // 准备退出

        Toast.makeText(this, "再按一次退出程序", Toast.LENGTH_SHORT).show();

        tExit = new Timer();

        tExit.schedule(new TimerTask() {

            @Override

            public void run() {

                isExit = false; // 取消退出

            }

        }, 2000); // 如果2秒钟内没有按下返回键，则启动定时器取消掉刚才执行的任务  

    } else {

        finish();

        System.exit(0);

    }

} 

//=======第二个方法===============================================

private long mExitTime;

if ((System.currentTimeMillis() - mExitTime) > 2000) {

    Toast.makeText(this, "在按一次退出", Toast.LENGTH_SHORT).show();

    mExitTime = System.currentTimeMillis();

    } else {

        finish();

    }