flutter - 在 flutter 中将 "Widget"添加为 "State"类中的字段时出错

Question

此类实现的目的

为 admin 显示不同的 View 和 user登录后 Scaffold body .

错误

使用 Widget 时显示以下错误作为 State<NormalMenuState> 内的字段类。

'_NormalMenuState.widget' ('() → Widget') isn't a valid override of 'State.widget' ('() → NormalMenuState')

代码

class NormalMenu extends StatelessWidget {
  final String userType;

  NormalMenu({this.userType});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: MyHomePage(this.userType),
    );
  }
}

class NormalMenuState extends StatefulWidget {
  final String userType;

  NormalMenuState(this.userType);

  @override
  State<StatefulWidget> createState() => _NormalMenuState(userType: this.userType);
}

class _NormalMenuState extends State<NormalMenuState> {
  String appTitle = 'Welcome';
  final String userType;
  Widget widget; //<= `This line shows error`

  _NormalMenuState({this.userType});

  @override
  void initState() {
    if (this.userType == UserType.admin) {
      this.appTitle = "User Information";
      widget = UserInformation();
    } else {
      this.appTitle = "Pay Fair";
      widget = BookTicket();
    }
    super.initState();
  }

Answer 1

如果你查看源代码:

abstract class State<T extends StatefulWidget> extends Diagnosticable {
  T get widget => _widget;

有一个widget getter 用于访问相关的StatefulWidget 类。问题不在于将 Widget 创建为实例字段，而是您的错误指出的名称:

'_NormalMenuState.widget' ('() → Widget') isn't a valid override of 'State.widget' ('() → NormalMenuState')

因此更改变量的名称:

Widget widget; => Widget myWidget;