双击返回按钮退出App

/** * 点击退出键土司再按一次退出程序 */private long exitTime = 0;@Overridepublic boolean onKeyDown(int keyCode, KeyEvent event) {    if (event.getAction() == KeyEvent.ACTION_DOWN && keyCode == KeyEvent.KEYCODE_BACK) {        if (System.currentTimeMillis() - exitTime > 2000) {            Toast.makeText(this, "再按一次退出智能APP", Toast.LENGTH_SHORT).show();            exitTime = System.currentTimeMillis();        } else {            finish();        }        return true;    }    return super.onKeyDown(keyCode, event);}