无法在此Provider<Movies> Widget之上找到正确的MyApp

Question

所以，我在一个应用程序中使用BLoC和提供者包。在我的“moviesprovider.dart”中，当应用程序第一次打开时，我从返回json的API中获取一些数据。如何从Provider.of中的main.dart (上下文)访问MultiProvider？基本上，我想访问列表电影的同一个实例，但不知道如何访问。

我所犯的错误：

错误:无法在此MyApp Widget之上找到正确的提供程序

这是因为您使用了不包括您选择的提供者的BuildContext。

代码：Main.dart

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

class MyApp extends StatelessWidget {
  MyApp({Key key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return MultiProvider(
      providers: [
        ChangeNotifierProvider.value(
          value: Movies(),
        ),
        Provider<SwipeBloc>(create: (_) {
          SwipeBloc()
            ..add(
              LoadMoviesEvent(
                movies: context.read<Movies>().movies,
              ),
            );
        }),
        ChangeNotifierProvider.value(
          value: User(),
        ),
        ChangeNotifierProvider.value(
          value: Auth(),
        ),
      ],
      child: ...
  }
}

movies_provider.dart

import 'dart:convert';

import 'package:flutter/material.dart';
import 'package:movies_recomendations/constants.dart';
import 'package:http/http.dart' as http;

import './single_movie_provider.dart';

class Movies with ChangeNotifier {
  String plotText = "";

  List<Movie> _movies = [];

  List<Movie> get movies {
    return <Movie>[..._movies];
  }

  .....

  Future<void> fetchAndSetMovies() async {
    const url = 'http://192.168.1.142:8000/Desktop/textData.json';

    try {
      final response = await http.get(
        Uri.parse(url),
      );
      String source = Utf8Decoder().convert(response.bodyBytes);

      final extractedData =
          List<Map<String, dynamic>>.from(json.decode(source));
      final List<Movie> loadedMovies = [];

      extractedData.forEach(
        ((movieInfo) => {
              loadedMovies.add(Movie(
                id: movieInfo['id'],
                age: 12,
                countries: List<String>.from(movieInfo['country']),
                description: movieInfo['descriprion'],
                frames: movieInfo['frames'],
                genre: movieInfo['genre'],
                poster: movieInfo['poster'],
                premiereWorld: movieInfo['date'].toString(),
                ratingIMDb: movieInfo['ratingIMDb'],
                ratingKinopoisk: movieInfo['ratingKinopoisk'],
                title: movieInfo['title'][1],
                ifSeries: movieInfo['ifSeries'],
                dateTo: movieInfo['dateTo'].toString(),
                isFavourite: true,
                seasons: movieInfo['seasons'],
              )),
            }),
      );
      _movies = loadedMovies;
      notifyListeners();
    } on Exception catch (e) {
      print('error');
      print(e.toString());
    }
  }
}

Swipe_event.dart

part of 'swipe_block.dart';

abstract class SwipeEvent extends Equatable {
  const SwipeEvent();

  @override
  List<Object> get props => [];
}

class LoadMoviesEvent extends SwipeEvent {
  final List<Movie> movies ;

  LoadMoviesEvent({
    required this.movies,
  });

  @override
  List<Object> get props => [movies];
}

class SwipeLeftEvent extends SwipeEvent {
  final Movie movie;

  SwipeLeftEvent({
    required this.movie,
  });

  @override
  List<Object> get props => [movie];
}

class SwipeRightEvent extends SwipeEvent {
  final Movie movie;

  SwipeRightEvent({
    required this.movie,
  });

  @override
  List<Object> get props => [movie];
}

Answer 1

您可能需要将调用Provider.of(context)的代码移动到它自己的小部件中。正如错误所暗示的那样，您不能使用提供程序在您用来设置提供程序作用域的同一个BuildContext中检索依赖项。创建一个新的小部件还会生成一个新的BuildContext。

如果确实需要在定义Provider.of(context)的同一个类中使用MultiProvider，则可以使用构建器小部件生成新的上下文。

Answer 2

因此，要解决这个问题，不应该在BlocProvider中使用main.dart。您应该在实现BLoC提供程序的直接小部件中使用它。所以我在一个屏幕引用中使用它，所以我把它写成这样

class RecomendationsScreen extends StatelessWidget {
  static const routeName = '/recomendations';

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      backgroundColor: kBackgroundColor,
      body: BlocProvider(
        create: (_) => SwipeBloc()
          ..add(
            LoadMoviesEvent(
              movies: Provider.of<Movies>(context).movies,
            ),
          ),
        child: RecomendationsBody(),
      ),
    );
  }
}