Firebase Dart 尝试读取在创建其值期间抛出的提供程序

Question

我现在正在开发一个身份验证系统，我遇到了这个错误：

Bad state: Tried to read a provider that threw during the creation of its value.
The exception occurred during the creation of type AuthenticationService.

这是我的 main.dart：

import 'package:flutter/material.dart';
import 'package:provider/provider.dart';
import 'package:twofound/authentication.dart';
import 'package:twofound/database.dart';
import 'package:twofound/swipe.dart';
import 'package:twofound/map.dart';
import 'package:twofound/offers.dart';
import 'package:twofound/friends.dart';
import 'package:twofound/profile.dart';
import 'package:twofound/splash.dart';
import 'package:twofound/login.dart';
import 'package:twofound/register.dart';
import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:firebase_auth/firebase_auth.dart';
import 'package:firebase_core/firebase_core.dart';

void main() async {
  WidgetsFlutterBinding.ensureInitialized();
  runApp(const MainSeite());
  await Firebase.initializeApp();
  connectToFireBase();
}

class MainSeite extends StatefulWidget {
  const MainSeite({Key? key}) : super(key: key);

  @override
  _MainSeiteState createState() => _MainSeiteState();
}

class _MainSeiteState extends State<MainSeite> {
  int currentIndex = 0;
  List<Widget> pages = [
    const RegisterForm(),
    const Swipe(),
    const Map(),
    const Chat(),
    const Contacts(),
    const Profile(),
  ];

  @override
  Widget build(BuildContext context) {
    return MultiProvider(
        providers: [
          Provider<AuthenticationService>(
            create: (_) => AuthenticationService(FirebaseAuth.instance),
          ),
          StreamProvider(
            create: (context) =>
                context.read<AuthenticationService>().authStateChanges,
            initialData: null,
          ),
        ],
        child: MaterialApp(
          home: Scaffold(
            bottomNavigationBar: BottomNavigationBar(
              backgroundColor: Colors.black,
              selectedItemColor: Colors.orange,
              unselectedItemColor: Colors.black,
              currentIndex: currentIndex,
              items: [
                BottomNavigationBarItem(
                    icon: Icon(Icons.people), label: "Swipe"),
                BottomNavigationBarItem(icon: Icon(Icons.map), label: "Map"),
                BottomNavigationBarItem(
                    icon: Icon(Icons.zoom_in_outlined),
                    label: "Activity Offers"),
                BottomNavigationBarItem(icon: Icon(Icons.chat), label: "Social")
              ],
              onTap: (index) {
                setState(() {
                  currentIndex = index;
                });
              },
            ),
            body: SafeArea(child: pages[currentIndex]),
          ),
        ));
  }
}

class AuthenticationWrapper extends StatelessWidget {
  const AuthenticationWrapper({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    final firebaseUser = context.watch<User?>();
    if (firebaseUser == null) {
      return const RegisterForm();
    }
    return const MainSeite();
  }
}

void connectToFireBase() async {
  final FirebaseAuth authenticate = FirebaseAuth.instance;
  UserCredential result = await authenticate.signInAnonymously();
  User user = result.user!;

  DatabaseService database = DatabaseService(user.uid);

  database.setEntry("Test", "test text");
}

我希望用户在退出 Firebase 时看到注册页面，在登录时看到主页。我使用可能导致该错误的提供商。

如果你能帮助我，我非常高兴，因为我是 dart 和 flutter 的新手。

Answer 1

如果没有 AuthenticationService 的源代码，就不可能说出导致异常的原因。请将其添加到您的问题中。另外，对于未来的问题，请考虑将问题范围缩小到似乎导致问题的最小代码位。但是，至少提供最小的、可重现的示例。

编辑：

AuthenticationService 的源看起来不错。异常来自 StreamProvider.create。这是在当前 BuildContext 中 authService 可用之前调用的 ctx.read 。像这样确定提供商的范围可以消除这个问题。

  @override
  Widget build(BuildContext context) {
    return Provider(
      create: (_) => AuthenticationService(FirebaseAuth.instance),
      child: StreamProvider(
          create: (ctx) => ctx.read<AuthenticationService>().authStateChanges,
          initialData: null,
          child: MaterialApp(),
      ),
    );
  }