点击两次退出应用

//两次点击返回退出程序
@Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
    boolean isExit = true;
    if(checkFragment== INDEX_CHARGE_FRAGMENT){ //充电fragment
        isExit = ChargeFragment.onKeyDown(keyCode, event);
    }
    if (isExit){
        if (keyCode == KeyEvent.KEYCODE_BACK && event.getAction() == KeyEvent.ACTION_DOWN) {
            if ((System.currentTimeMillis() - exitTime) > 2000) {
                ToastUtil.showToast(MainActivity.this,"再按一次退出程序");
                // ToastShow.showCustomDialog(MainActivity.this,"再按一次退出程序");
                exitTime = System.currentTimeMillis();
            } else {
                finish();
                System.exit(0);
            }
            return true;
        }
    }else{
        return true;
    }
    return super.onKeyDown(keyCode, event);
}