没有定义“statefulwidget.createstate”和 setstate 的具体实现

Question

我是上周刚学的 Flutter 的新手，在这里遇到两个问题，我正在尝试解决错误，但仍然无法解决，有人可以帮帮我吗？下面是飞镖代码。

'main.dart'

class Sharer extends StatefulWidget
{
  bool _isLoggedIn = false;
  Map userProfile;
  final facebookLogin = FacebookLogin();
  @override
  Widget build(BuildContext context)
  {
    return Scaffold(
      appBar: AppBar(
        backgroundColor: Colors.amber,
        centerTitle: true,
        title: Text('Welcome Sharer',
          style: TextStyle(
            fontSize: 16.0,
            color: Colors.black87,
            letterSpacing: 1.0,
          ),
        ),
      ),
      body:
      //Center(
        //child: isLoggedin
            //?
        Row(
          mainAxisAlignment: MainAxisAlignment.center,
          crossAxisAlignment: CrossAxisAlignment.center,
          children: <Widget>[
            Expanded(
              flex: 1,
              child: Container(
                padding: EdgeInsets.all(20.0),
                child: RaisedButton.icon(
                  onPressed: () async {
                    final result = await facebookLogin.logIn(['email']);

                    switch (result.status) {
                      case FacebookLoginStatus.loggedIn:
                        final token = result.accessToken.token;
                        final graphResponse = await http.get('https://graph.facebook.com/v2.12/me?fields=name,picture,email&access_token=${token}');
                        final profile = JSON.jsonDecode(graphResponse.body);
                        print(profile);
                        setState(() {
                          userProfile = profile;
                          _isLoggedIn = true;
                        });
                        break;

                      case FacebookLoginStatus.cancelledByUser:
                        setState(() => _isLoggedIn = false );
                        break;
                      case FacebookLoginStatus.error:
                        setState(() => _isLoggedIn = false );
                        break;
                    }
                    

                  },
                  icon: Icon(
                    MyFlutterApp.facebook,
                  ),
                  label: Text(
                    'Sharer',
                    style: TextStyle(
                      fontFamily: 'MyFlutterApp',
                      color: Colors.black87,
                      letterSpacing: 1.0,
                    ),
                  ),
                ),
              ),
            ),
          ],
        ),
      //),
    );
  }
}

错误显示在类名上说'缺少 statefulwidget.create state 的具体实现'另一个是'setstate is not defined'，我不知道有什么问题可以帮忙吗？ 谢谢和问候。

Answer 1

这是一个 StatefulWidget 实现的示例

class NameOfYourWidget extends StatefulWidget {
  @override
  _NameOfYourWidgetState createState() => _NameOfYourWidgetState();
}

class _NameOfYourWidgetState extends State<NameOfYourWidget> {
  @override
  Widget build(BuildContext context) {
    return Container(
      
    );
  }
}

对于您的代码，请改用它：

class Shared extends StatefulWidget {
  @override
  _SharedState createState() => _SharedState();
}

class _SharedState extends State<Shared> {
  bool _isLoggedIn = false;
  Map userProfile;
  final facebookLogin = FacebookLogin();
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        backgroundColor: Colors.amber,
        centerTitle: true,
        title: Text(
          'Welcome Sharer',
          style: TextStyle(
            fontSize: 16.0,
            color: Colors.black87,
            letterSpacing: 1.0,
          ),
        ),
      ),
      body:
          //Center(
          //child: isLoggedin
          //?
          Row(
        mainAxisAlignment: MainAxisAlignment.center,
        crossAxisAlignment: CrossAxisAlignment.center,
        children: <Widget>[
          Expanded(
            flex: 1,
            child: Container(
              padding: EdgeInsets.all(20.0),
              child: RaisedButton.icon(
                onPressed: () async {
                  final result = await facebookLogin.logIn(['email']);

                  switch (result.status) {
                    case FacebookLoginStatus.loggedIn:
                      final token = result.accessToken.token;
                      final graphResponse = await http.get(
                          'https://graph.facebook.com/v2.12/me?fields=name,picture,email&access_token=${token}');
                      final profile = JSON.jsonDecode(graphResponse.body);
                      print(profile);
                      setState(() {
                        userProfile = profile;
                        _isLoggedIn = true;
                      });
                      break;

                    case FacebookLoginStatus.cancelledByUser:
                      setState(() => _isLoggedIn = false);
                      break;
                    case FacebookLoginStatus.error:
                      setState(() => _isLoggedIn = false);
                      break;
                  }
                },
                icon: Icon(
                  MyFlutterApp.facebook,
                ),
                label: Text(
                  'Sharer',
                  style: TextStyle(
                    fontFamily: 'MyFlutterApp',
                    color: Colors.black87,
                    letterSpacing: 1.0,
                  ),
                ),
              ),
            ),
          ),
        ],
      ),
      //),
    );
  }
}

您可以在此处了解有关statefulwidget 的更多信息：

视频： Google Developers : How Stateful Widgets Are Used Best
Flutter Tutorial for Beginners- Stateful Widgets

文章： Let's build a simple Stateful Widget in Flutter

希望对你有帮助