参数类型 'Products Function(BuildContext, dynamic, dynamic)' 无法分配给参数类型 'Products Function(BuildContext)'

Question

我是新手，正在学习以前版本编写的 Flutter 教程，我在使用此代码时遇到以下错误：

main.ts:

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MultiProvider(
      providers: [
        ChangeNotifierProvider.value(
          value: Auth(),
        ),
        ChangeNotifierProxyProvider<Auth, Products>(
          create: (ctx, auth, previousProducts) => Products(
            auth.token,
            auth.userId,
            previousProducts == null ? [] : previousProducts.items,
          ),
        ),
        ChangeNotifierProvider.value(
          value: Cart(),
        ),
        ChangeNotifierProxyProvider<Auth, Orders>(
          create: (ctx, auth, previousOrders) => Orders(
            auth.token,
            auth.userId,
            previousOrders == null ? [] : previousOrders.orders,
          ),
        ),
      ],
      child: Consumer<Auth>(
        builder: (ctx, auth, _) => MaterialApp(
          title: 'MyShop',
          theme: ThemeData(
            primarySwatch: Colors.purple,
            textSelectionTheme: TextSelectionThemeData(
              selectionColor: Colors.deepOrange,
              selectionHandleColor: Colors.blue,
            ),
            fontFamily: 'Lato',
            pageTransitionsTheme: PageTransitionsTheme(
              builders: {
                TargetPlatform.android: CustomPageTransitionBuilder(),
                TargetPlatform.iOS: CustomPageTransitionBuilder(),
              },
            ),
          ),
          home: auth.isAuth
              ? ProductsOverviewScreen()
              : FutureBuilder(
                  future: auth.tryAutoLogin(),
                  builder: (ctx, authResultSnapshot) =>
                      authResultSnapshot.connectionState ==
                              ConnectionState.waiting
                          ? SplashScreen()
                          : AuthScreen(),
                ),
          routes: {
            ProductDetailScreen.routeName: (ctx) => ProductDetailScreen(),
            CartScreen.routeName: (ctx) => CartScreen(),
            OrdersScreen.routeName: (ctx) => OrdersScreen(),
            UserProductsScreen.routeName: (ctx) => UserProductsScreen(),
            EditProductScreen.routeName: (ctx) => EditProductScreen(),
          },
        ),
      ),
    );
  }
}

The named parameter 'update' is required, but there's no corresponding argument. Try adding the required argument.

The argument type 'Products Function(BuildContext, dynamic, dynamic)' can't be assigned to the parameter type 'Products Function(BuildContext)'.

所有错误都来自这部分代码（以及其他类似部分）：

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

这是 Products.ts:

import 'dart:convert';

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

import '../models/http_exception.dart';
import './product.dart';

class Products with ChangeNotifier {
  List<Product> _items = [];
  final String authToken;
  final String userId;

  Products(this.authToken, this.userId, this._items);

  List<Product> get items {
    // if (_showFavoritesOnly) {
    //   return _items.where((prodItem) => prodItem.isFavorite).toList();
    // }
    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([bool filterByUser = false]) async {
    final filterString =
        filterByUser ? 'orderBy="creatorId"&equalTo="$userId"' : '';
    var url = Uri.parse(
        'https://flutter-update.firebaseio.com/products.json?auth=$authToken&$filterString');
    try {
      final response = await http.get(url);
      final extractedData = json.decode(response.body) as Map<String, dynamic>;
      if (extractedData == null) {
        return;
      }
      url = Uri.parse(
          'https://flutter-update.firebaseio.com/userFavorites/$userId.json?auth=$authToken');
      final favoriteResponse = await http.get(url);
      final favoriteData = json.decode(favoriteResponse.body);
      final List<Product> loadedProducts = [];
      extractedData.forEach((prodId, prodData) {
        loadedProducts.add(Product(
          id: prodId,
          title: prodData['title'],
          description: prodData['description'],
          price: prodData['price'],
          isFavorite:
              favoriteData == null ? false : favoriteData[prodId] ?? false,
          imageUrl: prodData['imageUrl'],
        ));
      });
      _items = loadedProducts;
      notifyListeners();
    } catch (error) {
      throw (error);
    }
  }

  Future<void> addProduct(Product product) async {
    final url = Uri.parse(
        'https://flutter-update.firebaseio.com/products.json?auth=$authToken');
    try {
      final response = await http.post(
        url,
        body: json.encode({
          'title': product.title,
          'description': product.description,
          'imageUrl': product.imageUrl,
          'price': product.price,
          'creatorId': userId,
        }),
      );
      final newProduct = Product(
        title: product.title,
        description: product.description,
        price: product.price,
        imageUrl: product.imageUrl,
        id: json.decode(response.body)['name'],
      );
      _items.add(newProduct);
      // _items.insert(0, newProduct); // at the start of the list
      notifyListeners();
    } catch (error) {
      print(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.parse(
          'https://flutter-update.firebaseio.com/products/$id.json?auth=$authToken');
      await 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.parse(
        'https://flutter-update.firebaseio.com/products/$id.json?auth=$authToken');
    final existingProductIndex = _items.indexWhere((prod) => prod.id == id);
    Product? existingProduct = _items[existingProductIndex];
    _items.removeAt(existingProductIndex);
    notifyListeners();
    final response = await http.delete(url);
    if (response.statusCode >= 400) {
      _items.insert(existingProductIndex, existingProduct);
      notifyListeners();
      throw HttpException('Could not delete product.');
    }
    existingProduct = null;
  }
}

我不知道问题出在哪里，我应该如何解决这些错误？我在 Products class.

中找不到名为 update 的必需参数

Answer 1

不要使用ChangeNotifierProxyProvider创建新对象。这是一个提供者，它也依赖于其他对象来更新它的值。通过以下方式仅使用 Provider：

Provider(
  create: (_) => MyModel(),
  child: ...
)

这对于您的用例应该足够了。

Answer 2

我假设您正在学习 Maximillian 的 udemy 课程。您正在使用 ChangeNotifierProxy，因为您的产品提供商依赖于 Auth 提供商的变量。

ChangeNotifierProxyProvider<MyModel, MyChangeNotifier>(
create: (_) => MyChangeNotifier(),
update: (_, myModel, myNotifier) => myNotifier
..update(myModel),
child: ...
);

这是定义 ChangeNotifierProxyProvider 的方法。在您的情况下，它将是：

without null safety migration

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

with null safety migration

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

如果您看到任何与更新相关的错误，那么您需要升级您的软件包。

如果您还需要帮助，请告诉我:)

Answer 3

最后我可以通过修改代码解决我的问题：

providers: [
        ChangeNotifierProvider.value(
          value: Auth(),
        ),
        ChangeNotifierProxyProvider<Auth, Products>(
          create: (ctx) =>
              Products(null as String, null as String, null as List<Product>),
          update: (ctx, auth, previousProducts) => Products(
            auth.token as String,
            auth.userId as String,
            previousProducts == null ? [] : previousProducts.items,
          ),
        ),
        ChangeNotifierProvider.value(
          value: Cart(),
        ),
        ChangeNotifierProxyProvider<Auth, Orders>(
          create: (ctx) =>
              Orders(null as String, null as String, null as  List<OrderItem>),
          update: (ctx, auth, previousOrders) => Orders(
            auth.token as String,
            auth.userId as String,
            previousOrders == null ? [] : previousOrders.orders,
          ),
        ),
      ],

参数类型 'Products Function(BuildContext, dynamic, dynamic)' 无法分配给参数类型 'Products Function(BuildContext)'

The argument type 'Products Function(BuildContext, dynamic, dynamic)' can't be assigned to the parameter type 'Products Function(BuildContext)'

flutter

typeerror

non-nullable