安卓APP---点击两次退出

 @Override
    public boolean dispatchKeyEvent(KeyEvent event){
        if(event.getKeyCode() == KeyEvent.KEYCODE_BACK &&
                event.getAction() == KeyEvent.ACTION_DOWN && event.getRepeatCount() == 0){
            if ((System.currentTimeMillis() - exitTime) > 2000) {
                Toast.makeText(this, "再按一次退出程序", Toast.LENGTH_SHORT).show();
                exitTime = System.currentTimeMillis();
            } else {
                finish();
            }
            return true;
        }
        return super.dispatchKeyEvent(event);
    }
}