Flutter 使用 SnackBar 報 Scaffold.of() called with a context that does not contain a Scaffold. 錯誤的解決辦法

class LoginState extends State<LoginPage> {
  var _scaffoldkey = GlobalKey<ScaffoldState>();//把Scaffold的key自己保存

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      key: _scaffoldkey,//添加
      body: SingleChildScrollView(
        child: Column(
          crossAxisAlignment: CrossAxisAlignment.start,
          children: <Widget>[
            Container(
              child: GestureDetector(
                onTap: () {
                  final snackBar = SnackBar(content: Text("點擊按鈕"), duration: Duration(seconds: 1),);
                  //Scaffold.of(context).showSnackBar(snackbar); 修改爲
                  _scaffoldkey.currentState.showSnackBar(snackBar);
                },
                child: Text(S.of(context).register, style: TextStyle(color: Colors.blue, fontSize: 13),),
              ),
            ),
          ],
        ),
      ),
    );
  }
}