提供程序错误：找不到正确的提供程序-Flutter

Question

我正在使用Flutter提供程序，但是我遇到了这个问题，我进行了很多搜索，但找不到解决方案，也许我导入软件包的方式错误，更改了它，但仍然是相同的错误

这是我的提供商代码（AuthService）

import 'package:firebase_auth/firebase_auth.dart';
import 'dart:async';
import 'package:flutter/material.dart';

class AuthService with ChangeNotifier {
  final FirebaseAuth _auth = FirebaseAuth.instance;

  Future<FirebaseUser> getUser() {
    return _auth.currentUser();
  }


  Future logout() async {
    var result = FirebaseAuth.instance.signOut();
    notifyListeners();
    return result;
  }

  Future<FirebaseUser> loginUser({String email, String password}) async {
    try {
      var result = await FirebaseAuth.instance
          .signInWithEmailAndPassword(email: email, password: password);
      notifyListeners();
      return result.user;
    }  catch (e) {
      throw new AuthException(e.code, e.message);
    }
  }

  Future<FirebaseUser> signupUser({String email,String password}) async{
    try{
      var result = await FirebaseAuth.instance.createUserWithEmailAndPassword(email: email,password: password);
      notifyListeners();
      return result.user;
    }catch(e){
      throw new AuthException(e.code, e.message);
    }
  }
}

这是我的主要爱好，我在这里使用MultiProvider

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

import './providers/auth_service.dart';
import './screens/authenticate_screen.dart';
import './screens/edit_categories_screen.dart';
import './providers/categories.dart';
import './screens/category_screen.dart';
import './screens/categories_overview_screen.dart';
import './screens/add_item_screen.dart';

void main(List<String> args) {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MultiProvider(
      providers: [
        Provider<Categories>(
          create: (_) => Categories(),
        ),
        Provider<AuthService>(
          create: (_)=>AuthService(),
        )
      ],
      child: MaterialApp(
        title: 'Save All Me',
        theme: ThemeData(primarySwatch: Colors.purple),
        home: FutureBuilder<FirebaseUser>(
          future: Provider.of<AuthService>(context).getUser(),
          builder: (context, snapshot){
            if(snapshot.connectionState==ConnectionState.done){
              if(snapshot.error!=null){
                print('error');
                return Text(snapshot.error.toString());
              }
              return snapshot.hasData?CategoriesOverviewScreen(snapshot.data):AuthScreen();
            }else{
              return Center(child: CircularProgressIndicator());
            }
          },
        ),
        routes: {
          AddItemScreen.routeName: (context) => AddItemScreen(),
          CategoryScreen.routeName:(context)=>CategoryScreen(),
          EditCategoriesScreen.routeName:(context)=>EditCategoriesScreen(),
        },
      ),
    );
  }
}

and this is the error 任何帮助，请^^