在将ChangeNotifierProxyProvider添加到我的multiproviders后异步挂起

Question

我正在从Auth传递身份验证令牌。dart文件到产品。dart文件使应用程序能够获取我数据库中的产品，但应用程序无法获取这些，我是很新的扑动任何帮助将不胜感激

谢谢

这是我的Auth。飞镖文件

import 'dart:convert';
import 'package:flutter/widgets.dart';
import 'package:http/http.dart' as http;
import '../models/http_exceptions.dart';
class Auth with ChangeNotifier {
  String _token;
  DateTime _expiryDate;
  String _userId;
  bool get isAuth {
    return token != null;
  }
  String get token {
    if (_expiryDate != null &&
        _expiryDate.isAfter(DateTime.now()) &&
        _token != null) {
      return _token;
    }
    return null;
  }
  Future<void> _authenticate(
      String email, String password, String urlSegment) async {
    final url = Uri.parse(
      'https://identitytoolkit.googleapis.com/v1/accounts:$urlSegment?key=<key>',
    );
    try {
      final response = await http.post(
        url,
        body: json.encode(
          {
            'email': email,
            'password': password,
            'returnSecureToken': true,
          },
        ),
      );
      final responseData = json.decode(response.body);
      if (responseData['error'] != null) {
        throw HttpEception(responseData['error']['message']);
      }
      _token = responseData['idToken'];
      _userId = responseData['localId'];
      _expiryDate = DateTime.now().add(
        Duration(
          seconds: int.parse(responseData['expiresIn']),
        ),
      );
      notifyListeners();
    } catch (error) {
      throw error;
    }
  }
  Future<void> signup(String email, String password) async {
    return _authenticate(email, password, 'signUp');
  }
  Future<void> login(String email, String password) async {
    return _authenticate(email, password, 'signInWithPassword');
  }
}

这是我的产品。dart文件，该文件的Product类为

import 'package:flutter/foundation.dart';
import 'package:http/http.dart' as http;
import 'dart:convert';
import 'package:shop_app/models/http_exceptions.dart';
class Product with ChangeNotifier {
  final String id;
  final String title;
  final String description;
  final double price;
  final String imageUrl;
  bool isFavorite;
  Product({
    @required this.id,
    @required this.title,
    @required this.description,
    @required this.price,
    @required this.imageUrl,
    this.isFavorite = false,
  });
  Future<void> toggleFavoriteStatus() async {
    final url = Uri.https(
      '<confedential>.firebaseio.com',
      '/products/$id.json',
    );
    final oldStatus = isFavorite;
    isFavorite = !isFavorite;
    notifyListeners();
    final response = await http.patch(
      url,
      body: json.encode(
        {
          'isFavorite': isFavorite,
        },
      ),
    );
    if (response.statusCode >= 400) {
      isFavorite = oldStatus;
      notifyListeners();
      throw HttpEception('Could Not Change To Favourite');
    }
  }
}

import 'dart:convert';
import 'package:flutter/material.dart';
import 'package:http/http.dart' as http;
import 'package:shop_app/models/http_exceptions.dart';
import './product.dart';
class Products with ChangeNotifier {
  List<Product> _items = [];
  final String authToken;
  Products(this.authToken,this._items);
  List<Product> get items {
    return [..._items];
  }
  List<Product> get favoriteItems {
    return _items.where((prodItem) => prodItem.isFavorite).toList();
  }
  Product findById(String id) {
    return _items.firstWhere((prod) => prod.id == id);
  }
  Future<void> fetchAndSetProducts() async {
    final url = Uri.https(
      '<details>.firebaseio.com',
      '/products.json?auth=$authToken',
    );
    try {
      final response = await http.get(url);
      // print(json.decode(response.body));
      final extractedData = json.decode(response.body) as Map<String, dynamic>;
      if (extractedData == null) {
        return;
      }
      final List<Product> loadedProducts = [];
      extractedData.forEach((productId, productData) {
        loadedProducts.add(
          Product(
            id: productId,
            title: productData['title'],
            description: productData['description'],
            price: productData['price'],
            isFavorite: productData['isFavourite'],
            imageUrl: productData['imageUrl'],
          ),
        );
      });
      _items = loadedProducts;
      notifyListeners();
    } catch (error) {
      throw error;
    }
  }
  Future<void> addProduct(Product product) async {
    var url = Uri.https(
      '<details>.firebaseio.com',
      '/products.json',
    );
    try {
      final response = await http.post(
        url,
        body: json.encode(
          {
            'title': product.title,
            'description': product.description,
            'imageUrl': product.imageUrl,
            'price': product.price,
            'isFavourite': product.isFavorite,
          },
        ),
      );
      final newProduct = Product(
        title: product.title,
        description: product.description,
        price: product.price,
        imageUrl: product.imageUrl,
        id: json.decode(response.body)['name'],
      );
      _items.add(newProduct);
      notifyListeners();
    } catch (error) {
      throw error;
    }
  }
  Future<void> updateProduct(String id, Product newProduct) async {
    final prodIndex = _items.indexWhere((prod) => prod.id == id);
    if (prodIndex >= 0) {
      final url = Uri.https(
        '<details>.firebaseio.com',
        '/products/$id.json',
      );
      http.patch(
        url,
        body: json.encode(
          {
            'title': newProduct.title,
            'description': newProduct.description,
            'imageUrl': newProduct.imageUrl,
            'price': newProduct.price,
          },
        ),
      );
      _items[prodIndex] = newProduct;
      notifyListeners();
    } else {
      print('...');
    }
  }
  Future<void> deleteProduct(String id) async {
    final url = Uri.https(
      '<details>.firebaseio.com',
      '/products/$id.json',
    );
    final exisitingProductIndex = _items.indexWhere((prod) => prod.id == id);
    var exisitingProduct = _items[exisitingProductIndex];
    _items.removeAt(exisitingProductIndex);
    notifyListeners();
    final response = await http.delete(url);
    if (response.statusCode >= 400) {
      _items.insert(exisitingProductIndex, exisitingProduct);
      notifyListeners();
      throw HttpEception('Could Not Delete Product.');
    }
    exisitingProduct = null;
  }
}

最后是main。Dart文件使用了所有这些

import 'package:flutter/material.dart';
import 'package:provider/provider.dart';
import './providers/auth.dart';
import './screens/cart_screen.dart';
import './screens/products_overview_screen.dart';
import './screens/product_detail_screen.dart';
import './providers/products.dart';
import './providers/cart.dart';
import './providers/orders.dart';
import './screens/orders_screen.dart';
import './screens/user_products_screen.dart';
import './screens/edit_product_screen.dart';
import './screens/auth_screen.dart';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MultiProvider(
      // Defining these providers for lisening to changes in the data
      providers: [
        ChangeNotifierProvider.value(
          value: Auth(),
        ),
        // First parameter is the type of data that we depened on and second is the data that we arre passing
        ChangeNotifierProxyProvider<Auth, Products>(
          update: (ctx, auth, previousProducts) => Products(
            auth.token,
            previousProducts == null ? [] : previousProducts.items,
          ),
        ),
        ChangeNotifierProvider.value(
          value: Cart(),
        ),
        ChangeNotifierProvider.value(
          value: Orders(),
        ),
      ],
      child: Consumer<Auth>(
        builder: (context, auth, _) => MaterialApp(
          title: 'MyShop',
          theme: ThemeData(
            primarySwatch: Colors.purple,
            accentColor: Colors.deepOrange,
            fontFamily: 'Lato',
          ),
          // home: ProductsOverviewScreen(),
          home: auth.isAuth ? ProductsOverviewScreen() : AuthScreen(),
          routes: {
            ProductDetailScreen.routeName: (ctx) => ProductDetailScreen(),
            CartScreen.routeName: (ctx) => CartScreen(),
            OrdersScreen.routeName: (ctx) => OrdersScreen(),
            UserProductsScreen.routeName: (ctx) => UserProductsScreen(),
            EditProductScreen.routeName: (ctx) => EditProductScreen(),
          },
        ),
      ),
    );
  }
}

Answer 1

刚刚添加了create到ChangeNotifierProxyProvider

ChangeNotifierProxyProvider<Auth, Products>(
          create: (_)=>Products('',[]),
          update: (ctx, auth, previousProducts) => Products(
            auth.token,
            previousProducts == null ? [] : previousProducts.items,
          ),
        ),

并更改了product中的url字符串。飞镖文件

    Uri url = Uri.parse(
        'https://<some_details>.firebaseio.com/products.json?auth=$authToken');