StreamProvider：错误：在此 App Widget 上方找不到正确的 Provider<User>

Question

我在我的 flutter-firebase 应用程序中使用提供程序包中的 StreamProvider 来实现身份验证功能，就像本教程 https://www.youtube.com/watch?v=j_SJ7XmT2MM&list=PL4cUxeGkcC9j--TKIdkb3ISfRbJeJYQwC&index=9 中解释的那样。

在尝试运行我的应用程序时，我收到一条错误消息，并建议如何正确执行此操作，但我的代码是按照建议的方式编写的。

void main() {
  WidgetsFlutterBinding.ensureInitialized();
  runApp(FirebaseWrapper());
  runApp(App());
}

class FirebaseWrapper extends StatelessWidget {
  // Create the initialization Future outside of build():
  final Future<FirebaseApp> _initialization = Firebase.initializeApp();
  // final Future<void> _initSharedPrefs = SharedPrefsHelper().initSharedPrefsInstance();

  @override
  Widget build(BuildContext context) {
    SystemChrome.setPreferredOrientations([DeviceOrientation.portraitUp]);
    return FutureBuilder(
      // from: https://firebase.flutter.dev/docs/overview/#initializing-flutterfire
      future: _initialization,
      // future: Future.wait([_initialization, _initSharedPrefs]),
      builder: (context, snapshot) {
        if (snapshot.hasError) return ErrorPage(); //TODO better error pages
        if (snapshot.connectionState == ConnectionState.done) return FirebaseAuthWrapper();
        return Loading(); //waiting
      },
    );
  }
}

class FirebaseAuthWrapper extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return StreamProvider<User>.value(
      value: Auth().userStream,
      initialData: null,
      child: App(),
    );
  }
}

class App extends StatefulWidget {
  @override
  _AppState createState() => _AppState();
}

class _AppState extends State<App> {
  @override
  Widget build(BuildContext context) {
    final user = Provider.of<User>(context);
    print('yeet');

    return MaterialApp(
      key: UniqueKey(),
      title: 'Wanderapp',
      theme: ThemeData(primarySwatch: Colors.blue),
      initialRoute: (user == null) ? '/signIn' : '/',
      routes: (user == null)
          ? {
              '/signIn': (context) => SignIn(),
              '/register': (context) => Register(),
              // '/forgotPassword': (context) => ForgotPassword(),
            }
          : {
              '/': (context) => Home(),
              //...
            },
    );
  }
}

错误信息：

Error: Could not find the correct Provider<User> above this App Widget

This happens because you used a `BuildContext` that does not include the provider
of your choice. There are a few common scenarios:

- You added a new provider in your `main.dart` and performed a hot-reload.
  To fix, perform a hot-restart.

- The provider you are trying to read is in a different route.

  Providers are "scoped". So if you insert of provider inside a route, then
  other routes will not be able to access that provider.

- You used a `BuildContext` that is an ancestor of the provider you are trying to read.

  Make sure that App is under your MultiProvider/Provider<User>.
  This usually happens when you are creating a provider and trying to read it immediately.

  For example, instead of:

  ```
  Widget build(BuildContext context) {
    return Provider<Example>(
      create: (_) => Example(),
      // Will throw a ProviderNotFoundError, because `context` is associated
      // to the widget that is the parent of `Provider<Example>`
      child: Text(context.watch<Example>()),
    ),
  }
  ```

  consider using `builder` like so:

  ```
  Widget build(BuildContext context) {
    return Provider<Example>(
      create: (_) => Example(),
      // we use `builder` to obtain a new `BuildContext` that has access to the provider
      builder: (context) {
        // No longer throws
        return Text(context.watch<Example>()),
      }
    ),
  }
  ```

我是 Firebase 中 StreamProvider 和 Provider.of 的相同“用户”类的用户，层次结构/范围在我的代码中似乎也是正确的，但它不起作用。 有谁知道我的错误是什么？非常感谢。

Answer 1

在这个link 关于runApp 它说：

再次调用 runApp 将从 屏幕并在其位置附加给定的小部件。

因此，您只需要删除第二个runApp，因为无论如何都会从StreamProvider 调用App：child: App(),。

解决方案：

void main() {
  WidgetsFlutterBinding.ensureInitialized();
  runApp(FirebaseWrapper());
  runApp(App()); //*** Remove this line ***///
}