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

Question

我是一名新学习者，正在学习以前版本中编写的 Flutter 教程，并且此代码出现以下错误:

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;
  }
}

我不知道问题是什么以及应该如何解决这些错误？我在 Products 类中找不到名为 update 的必需参数。

Answer 1

我假设您正在学习 Maximillian 的 udemy 类(class)。您正在使用 ChangeNotifierProxy，因为您的产品提供程序依赖于身份验证提供程序的变量。

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

这是定义 ChangeNotifierProxyProvider 的方法。 对于您的情况，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:)