为什么 BlocProvider 使用 null-safety 获取这两个错误？

Question

错误一：

error: 'Null' doesn't conform to the bound 'BlocBase<Object?>' of the type parameter 'T'. (type_argument_not_matching_bounds 

错误 2：

error: Couldn't infer type parameter 'T'.
Tried to infer 'Null' for 'T' which doesn't work:
  Type parameter 'T' is declared to extend 'BlocBase<Object?>' producing 'BlocBase<Object?>'.
The type 'Null' was inferred from:
  Parameter 'create' declared as     'T Function(BuildContext)'
                     but argument is 'Null Function(BuildContext)'.

考虑将显式类型参数传递给泛型。

(could_not_infer 在 [g_movies] lib\layout\movies_layout.dart:12)

    class MoviesLayout extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return BlocProvider(
      create: (BuildContext context) {
        MoviesCubit()..getTopRatedData();
      },
      child: BlocConsumer<MoviesCubit, MoviesStates>(
        listener: (context, state) {},
        builder: (context, state) {
          return Scaffold(
            appBar: AppBar(
              title: Text(
                'GMovies',
                style: GoogleFonts.oswald(
                  fontWeight: FontWeight.bold,
                  fontSize: 24,
                  color: defaultColor,
                ),
              ),
              actions: [
                Padding(
                  padding: const EdgeInsets.symmetric(horizontal: 20),
                  child: CircleAvatar(
                    radius: 20,
                    child: IconButton(
                      icon: Icon(Icons.person),
                      onPressed: () {},
                    ),
                  ),
                ),
              ],
            ),
            body: SingleChildScrollView(
              child: Padding(
                padding: const EdgeInsets.all(20.0),
                child: Column(
                  children: [
                    ExpandablePanel(
                      theme: ExpandableThemeData(
                        headerAlignment: ExpandablePanelHeaderAlignment.center,
                      ),
                      header: Row(
                        children: [
                          Text(
                            'Top Rated',
                            style: TextStyle(
                              fontWeight: FontWeight.bold,
                              fontSize: 22,
                            ),
                          ),
                          SizedBox(
                            width: 5,
                          ),
                          Text(
                            'Movies',
                            style: TextStyle(
                              fontSize: 22,
                            ),
                          ),
                        ],
                      ),
                      collapsed: SizedBox(
                        height: 2,
                      ),
                      expanded: SizedBox(
                        width: double.infinity,
                        height: 200,
                        child: ListView.separated(
                          shrinkWrap: true,
                          scrollDirection: Axis.horizontal,
                          itemBuilder: (context, index) => movieItem(),
                          separatorBuilder: (context, index) => SizedBox(
                            width: 10,
                          ),
                          itemCount: 10,
                        ),
                      ),
                    ),
                    SizedBox(
                      height: 10,
                    ),
                    ExpandablePanel(
                      theme: ExpandableThemeData(
                        headerAlignment: ExpandablePanelHeaderAlignment.center,
                      ),
                      header: Row(
                        children: [
                          Text(
                            'Popular',
                            style: TextStyle(
                              fontWeight: FontWeight.bold,
                              fontSize: 22,
                            ),
                          ),
                          SizedBox(
                            width: 5,
                          ),
                          Text(
                            'Movies',
                            style: TextStyle(
                              fontSize: 22,
                            ),
                          ),
                        ],
                      ),
                      collapsed: SizedBox(
                        height: 2,
                      ),
                      expanded: SizedBox(
                        width: double.infinity,
                        height: 200,
                        child: ListView.separated(
                          shrinkWrap: true,
                          scrollDirection: Axis.horizontal,
                          itemBuilder: (context, index) => movieItem(),
                          separatorBuilder: (context, index) => SizedBox(
                            width: 10,
                          ),
                          itemCount: 10,
                        ),
                      ),
                    ),
                    SizedBox(
                      height: 10,
                    ),
                    ExpandablePanel(
                      theme: ExpandableThemeData(
                        headerAlignment: ExpandablePanelHeaderAlignment.center,
                      ),
                      header: Row(
                        children: [
                          Text(
                            'Coming',
                            style: TextStyle(
                              fontWeight: FontWeight.bold,
                              fontSize: 22,
                            ),
                          ),
                          SizedBox(
                            width: 5,
                          ),
                          Text(
                            'Soon',
                            style: TextStyle(
                              fontSize: 22,
                            ),
                          ),
                        ],
                      ),
                      collapsed: SizedBox(
                        height: 2,
                      ),
                      expanded: SizedBox(
                        width: double.infinity,
                        height: 200,
                        child: ListView.separated(
                          shrinkWrap: true,
                          scrollDirection: Axis.horizontal,
                          itemBuilder: (context, index) => movieItem(),
                          separatorBuilder: (context, index) => SizedBox(
                            width: 10,
                          ),
                          itemCount: 10,
                        ),
                      ),
                    ),
                    SizedBox(
                      height: 10,
                    ),
                    ExpandablePanel(
                      theme: ExpandableThemeData(
                        headerAlignment: ExpandablePanelHeaderAlignment.center,
                      ),
                      header: Row(
                        children: [
                          Text(
                            'Now',
                            style: TextStyle(
                              fontWeight: FontWeight.bold,
                              fontSize: 22,
                            ),
                          ),
                          SizedBox(
                            width: 5,
                          ),
                          Text(
                            'Playing',
                            style: TextStyle(
                              fontSize: 22,
                            ),
                          ),
                        ],
                      ),
                      collapsed: SizedBox(
                        height: 2,
                      ),
                      expanded: SizedBox(
                        width: double.infinity,
                        height: 200,
                        child: ListView.separated(
                          shrinkWrap: true,
                          scrollDirection: Axis.horizontal,
                          itemBuilder: (context, index) => movieItem(),
                          separatorBuilder: (context, index) => SizedBox(
                            width: 10,
                          ),
                          itemCount: 10,
                        ),
                      ),
                    ),
                  ],
                ),
              ),
            ),
          );
        },
      ),
    );
  }

Answer 1

替换 MoviesCubit()..getTopRatedData(); 和 return MoviesCubit()..getTopRatedData();

或替换

create: (BuildContext context) {
        MoviesCubit()..getTopRatedData();
      }

和
create: (_) -> MoviesCubit()..getTopRatedData()