推送新路线时，flutter_bloc库中的存储库提供程序不提供存储库 [英] Repository provider in the flutter_bloc library doesn't provide repository with when pushing new route

问题描述

我正在使用flutter_bloc库来构建我的应用程序。除了BlocProvider之外，我还使用存储库提供程序，因为我将在整个应用程序中广泛使用特定的存储库。但是我在上下文方面有一个问题。以下是我的代码段：

I am using the flutter_bloc library to architect my app. In addition to the BlocProvider I am using the Repository Provider, since I will be using a specific repository extensively throughout my app. But I am having an issue with regards to context . Below is snippets of my code:

main.dart

void main() async {
  .......
  appRepository _appRepository = AppRepository();
  SystemChrome.setPreferredOrientations([DeviceOrientation.portraitUp])
      .then((_) {
    runApp(
      BlocProvider(
        builder: (context) =>
            AuthenticationBloc(appRepository: _appRepository)..dispatch(AppStarted()),
        child: App(appRepository: _appRepository,),
      ),
    );
  });
}

class App extends StatelessWidget {

............
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      home: BlocBuilder<AuthenticationBloc, AuthenticationState>(
        builder: (BuildContext context, AuthenticationState state) {
       .....
          if (state is AuthenticationUnauthenticated) {
            return SafeArea(
              top: false,
              bottom: false,
              child: RepositoryProvider(
                builder: (context) => _appRepository,
                child: LoginPage(firebaseMessaging: _firebaseMessaging),
              ),
            );
          }
      ......

        },
      ),
    );
  }
}

在登录表单中找到注册按钮：

register_button.dart

class RegisterButton extends StatelessWidget {
  final FirebaseMessaging _firebaseMessaging;

  RegisterButton({
    Key key,
    @required FirebaseMessaging firebaseMessaging,
  })  : assert(firebaseMessaging != null),
        _firebaseMessaging = firebaseMessaging,
        super(key: key);

  @override
  Widget build(BuildContext context) {
    return Row(
      mainAxisAlignment: MainAxisAlignment.center,
      children: <Widget>[
        Text("Don't have an account?", style: TextStyle(color: Colors.black)),
        SizedBox(width: 4.0),
        GestureDetector(
          child: Text("Register here!",
              style: TextStyle(
                  color: Color(0xFF585B8D), fontWeight: FontWeight.w500)),
          onTap: () {
            Navigator.of(context).push(
              MaterialPageRoute(builder: (context) {
                return RegisterPage(
                  firebaseMessaging: _firebaseMessaging,
                );
              }),
            );
          },
        )
      ],
    );
  }

register_page.dart

class RegisterPage extends StatelessWidget {
  final FirebaseMessaging _firebaseMessaging;

  RegisterPage({
    Key key,
    @required FirebaseMessaging firebaseMessaging,
  })  : assert(firebaseMessaging != null),
        _firebaseMessaging = firebaseMessaging,
        super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: BlocProvider(
        builder: (context) => RegisterBloc(
          appRepository: RepositoryProvider.of<AppRepository>(context),
          firebaseMessaging: _firebaseMessaging,
        ),
        child: RegisterForm(),
      ),
    );
  }
}

问题：

当我单击登录表单上的注册按钮时，出现以下错误：

I'm getting an error when I click on the register button on my login form that says the following:

No ancestor could be found starting from the context that was passed to RepositoryProvider.of<AppRepository>().

This can happen if:
1. The context you used comes from a widget above the RepositoryProvider.
2. You used MultiRepositoryProvider and didn't explicity provide the RepositoryProvider types.

Good: RepositoryProvider<AppRepository>(builder: (context) => AppRepository())
Bad: RepositoryProvider(builder: (context) => AppRepository()).

The context used was: BlocProvider<RegisterBloc>(dirty, state: _DelegateWidgetState#a87b2(lifecycle state: created))

为什么会出现此错误？如果在主函数中将存储库提供程序作为blocprovider的子级，将应用程序作为子存储库提供程序，然后在App（）中删除单个存储库提供程序，则似乎可以解决此问题。我猜问题出在按下按钮上的材料页面路线。我认为我不了解上下文或提供程序在Flutter中的工作原理。我以为提供商会为存储库/块查找小部件树，推送路由是否会破坏这种连续性？

Why am I getting this error? This problem seems to be fixed if I put the repository provider as the child of the blocprovider and app as the child repository provider in the main function and then deleting the invidual repository providers in App(). I'm guessing the issue is from pushing the material page route from the button. I don't think I understand how context or provider exactly works in Flutter. I thought the provider would look up the widget tree for the repository/bloc, does pushing a route some how break this continuity?

推荐答案

使用 Navigator.of（context）.push 或 Navigator.of（context）.pushNamed 所推送的小部件不是调用 Navigator.of（context）.push 或 Navigator.of（context）.pushNamed ，此小部件是 Navigator 包含给定的上下文，在您的情况下， Navigator 由 MaterialApp ，因此如果要将存储库或 Bloc 提供给其他 routes ， Provider 必须是 Navigator 的父级，成为 MaterialApp 的父母。

When you use Navigator.of(context).push or Navigator.of(context).pushNamed the widget pushed is not a child of the widget that call Navigator.of(context).push or Navigator.of(context).pushNamed, this widget is a child of the closest instance of Navigator that encloses the given context, in your case the Navigator is created by the MaterialApp, so if you want to provide the Repository or Bloc to different routes, the Provider must be a parent of the Navigator, in your case must be a parent of MaterialApp.

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