Android 双击返回键退出功能的实现

private boolean appExit=false;public Handler mHandler=new Handler(){    @Override    public void handleMessage(Message msg) {        if(msg.what==0){            appExit=false;        }    }};@Override public void onBackPressed() {    if(appExit){        finish();    }else{        appExit=true;        Toast.makeText(this,"再按一次退出",2000).show();//延迟两秒发送        mHandler.sendEmptyMessageDelayed(0,2000);    }}

@Override    public boolean onKeyUp(int keyCode, KeyEvent event) {        if (keyCode == KeyEvent.KEYCODE_BACK) {            if ((System.currentTimeMillis() - exitTime) > 2000) {                ToastUtil.showToast(this, R.string.hint_back_up);                exitTime = System.currentTimeMillis();            } else {                finish();            }        }        return true;    }