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;
}