按两次退出程序

@Override    public void onBackPressed() {        back2App();    }    private boolean isBack = false;    private Handler backHandler = new Handler() {        @Override        public void handleMessage(Message msg) {            super.handleMessage(msg);            isBack = false;        }    };    private void back2App() {        if (isBack) {            finish();        } else {            isBack = true;            Toast.makeText(mContext, "再按一次退出程序", Toast.LENGTH_SHORT).show();            backHandler.sendEmptyMessageDelayed(0, 2000);        }    }