参数类型“Widget Function(BuildContext, T, Widget)”不能分配给参数类型“Widget Function(BuildContext, T, Widget?)”

Question

i have been following a tutorial to implement state management into our flutter web app. This is the tutorial: https://medium.flutterdevs.com/firebase-authentication-using-provider-in-flutter-522841a2ee4d

Now i am creating the "baseView" model for my widgets and am a bit lost because i am new to flutter.

class BaseView<T extends BaseModel> extends StatefulWidget {
  final Widget Function(BuildContext context, T model, Widget child) builder;

  const BaseView({
    @required this.builder,
  });

  @override
  _BaseViewState<T> createState() => _BaseViewState<T>();
}

class _BaseViewState<T extends BaseModel> extends State<BaseView<T>> {
  T model = locator<T>();

  @override
  Widget build(BuildContext context) {
    return ChangeNotifierProvider<T>.value(
      //builder: (context) => model,
      child: Consumer<T>(builder: widget.builder),
      //notifier: model,
      value: model,
    );
  }
}

Firstly i get the error message for the "@required this.builder" part: The parameter 'builder' can't have a value of 'null' because of its type, but the implicit default value is 'null'.

And for the "Consumer(builder: widget.builder)" part i get this error: The argument type 'Widget Function(BuildContext, T, Widget)' can't be assigned to the parameter type 'Widget Function(BuildContext, T, Widget?)'.

I also have the link to the Github repo of the project, which is presented in the tutorial: https://github.com/flutter-devs/flutter_auth_provider

Any help is kindly appreciated!

Answer 1

Widget Function(BuildContext, T, Widget) cannot accept a null value for the widget, which is required by the Widget Function(BuildContext, T, Widget?) signature.

That's it. Make sense?