我尝试使用Bloc，但我的BlocProvider返回错误：

The method 'BlocProvider' isn't defined for the type '_MyAppState'.
Try correcting the name to the name of an existing method, or defining a method named 'BlocProvider'.

我找不到解决这个问题的方法。
这是我正在使用的代码

import 'package:app_13/post_cubit.dart';
import 'package:app_13/post_view.dart';
import 'package:flutter/material.dart';
import 'package:bloc/bloc.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatefulWidget {
  @override
  State<StatefulWidget> createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: BlocProvider<PostsCubit> (
        create: (context) => PostsCubit(),
        child: PostsView(),
      ),
    );
  }
}

并在pub.yaml中添加flutter_bloc

bloc: ^8.1.0

我做错了什么？为什么无法识别BlocProvider？
先谢谢你的帮助。