Dart 在Flutter中通过 Function(T) 传递泛型类型

我正在try 创建一个通用的使用者小部件，以便于将ViewModel传递给它的子级.因此，我有两个函数.一个在初始化ViewModel之后具有函数(T)，另一个用于将模型传递给子Widget.

泛型类中是ChangeNotifier的子类，在我想要在两个函数中发送T值之前，它工作得很好.

然后，我得到以下错误:

type '(OnBoardingViewModel) => Null' is not a subtype of type '(ChangeNotifier) => void'

和

type '(BuildContext, OnBoardingViewModel, Widget) => Scaffold' is not a subtype of type '(BuildContext, ChangeNotifier, Widget) => Widget'

但是，当我将扩展类型从ChangeNotifier更改为OnBoardingViewModel时，一切工作正常.

can someone help me 和 or explain why this ain't working??

import 'package:flutter/material.dart';
import 'package:get_it/get_it.dart';
import 'package:provider/provider.dart';

class StateFullConsumerWidget<T extends ChangeNotifier> extends StatefulWidget{

  StateFullConsumerWidget({@required this.builder,Key key,this.onPostViewModelInit,this.child}) : super(key : key);

  final Widget Function(BuildContext context, ChangeNotifier value, Widget child) builder;
  final Widget child;

  final void Function(T) onPostViewModelInit;

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

class _StateFullConsumerWidgetState<T extends ChangeNotifier> extends State<StateFullConsumerWidget>{
  T _viewModel;
  @override
  void initState() {
    // assign the model once when state is initialised
    _viewModel = GetIt.instance.get<T>();
    widget.onPostViewModelInit(_viewModel);


    super.initState();
  }
  @override
  Widget build(BuildContext context) {
    return ChangeNotifierProvider<T>(
      builder: (context) => _viewModel,
      child: Consumer<T>(
        builder: widget.builder,
        child: widget.child,
      ),
    );
  }

}

我的小部件

StateFullConsumerWidget<OnBoardingViewModel>(
      onPostViewModelInit: (viewModel){
        buildIntroList(viewModel);
        viewModel.maxPages = _introWidgetsList.length;
      },
      builder: (context,viewModel,child) {
        return Scaffold(
          key: widget.scaffoldKey,
          body: SafeArea(
            child: Container(),
            ),
          ),
        );
      },
    );

我的视图模型

import 'package:flutter/material.dart';

class OnBoardingViewModel extends ChangeNotifier{

  OnBoardingViewModel(){

  }
}