再按一次退出程序

    @Override
    public boolean onKeyDown(int keyCode, KeyEvent event)
    {
        if (keyCode == KeyEvent.KEYCODE_BACK)
        {
            if (isExit == false)
            {
                isExit = true;
                Toast.makeText(this, "再按一次退出程序", Toast.LENGTH_SHORT).show();
                if (!hasTask)
                {
                    tExit.schedule(taskExitCheck, 2000);
                }
            } else
            {
                finish();
            }
            return false;
        }
        return super.onKeyDown(keyCode, event);
    }

    private Boolean isExit = false;
    private Boolean hasTask = false;
    Timer tExit = new Timer();
    TimerTask taskExitCheck = new TimerTask()
    {
        @Override
        public void run()
        {
            isExit = false;
            hasTask = true;
        }
    };