错误：类型“CartItem”不是类型转换中类型“CartItem”的子类型，其中

Question

我最近开始学习Flutter。 当我点击“立即订购”时，出现错误： 类型“CartItem”不是类型转换中类型“CartItem”的子类型，其中 当我单击“立即订购”按钮时，我必须进入空白订单屏幕。 如果我不添加演员表，我会收到错误

The argument type 'List<CartItem>' can't be assigned to the parameter type 'List<CartItem>'

class CartScreen extends StatelessWidget {
  static const routeName = '/cart';

  const CartScreen({super.key});

  @override
  Widget build(BuildContext context) {
    final cart = Provider.of<Cart>(context);
    final orders = Provider.of<Orders>(context);

    return Scaffold(
      appBar: AppBar(
        title: Text(
          'Your cart',
          style: Theme.of(context).textTheme.bodyLarge,
        ),
      ),
      body: Column(
        children: [
          Card(
            margin: const EdgeInsets.all(15),
            child: Padding(
              padding: const EdgeInsets.all(8),
              child: Row(
                mainAxisAlignment: MainAxisAlignment.spaceBetween,
                children: [
                  const Text(
                    'Total',
                    style: TextStyle(fontSize: 20),
                  ),
                  Consumer<Cart>(
                    builder: (BuildContext context, Cart cart, Widget? widget) {
                      return Chip(
                        label: Text(
                          '\$${cart.totalAmount}',
                        ),
                        backgroundColor: Colors.white,
                      );
                    },
                  ),
                  ElevatedButton(
                     onPressed: () {
                      orders.addOrder(
                        cart.items.values.cast<CartItem>().toList(),
                        cart.totalAmount,
                      );
                      cart.clear();
                    },
                    child: Text(
                      'ORDER NOW',
                      style: Theme.of(context).textTheme.bodyMedium,
                    ),
                  ),
                ],
              ),
            ),
          ),
          Expanded(
            child: ListView.builder(
              itemBuilder: (context, index) => CartItem(
                id: cart.items.values.toList()[index].id,
                productId: cart.items.keys.toList()[index],
                title: cart.items.values.toList()[index].title,
                quantity: cart.items.values.toList()[index].quantity,
                price: cart.items.values.toList()[index].price,
              ),
              itemCount: cart.itemCount,
            ),
          ),
        ],
      ),
    );
  }
}

订单

class OrderItem {
  final String id;
  final double amount;
  final List<CartItem> products;
  final DateTime dateTime;

  const OrderItem({
    required this.id,
    required this.amount,
    required this.products,
    required this.dateTime,
  });
}

class Orders with ChangeNotifier {
  final List<OrderItem> _orders = [];

  List<OrderItem> get orders {
    return [..._orders];
  }

  void addOrder(
    List<CartItem> cartProducts,
    double total,
  ) {
    _orders.insert(
      0,
      OrderItem(
        id: DateTime.now().toString(),
        amount: total,
        products: cartProducts,
        dateTime: DateTime.now(),
      ),
    );
    notifyListeners();
  }
}

购物车

class CartItem {
  final String id;
  final String title;
  final int quantity;
  final double price;

  CartItem({
    required this.id,
    required this.title,
    required this.quantity,
    required this.price,
  });
}

class Cart with ChangeNotifier {
  late Map<String, CartItem> _items = {};

  Map<String, CartItem> get items {
    return {..._items};
  }

  int get itemCount {
    return _items.length;
  }

  double get totalAmount {
    double total = 0.0;
    _items.forEach((key, cartItem) {
      total += cartItem.price * cartItem.quantity;
    });
    return total;
  }

  void addItem(
    String productId,
    double price,
    String title,
  ) {
    if (_items.containsKey(productId)) {
      _items.update(
        productId,
        (existingCartItem) => CartItem(
          id: existingCartItem.id,
          title: existingCartItem.title,
          quantity: existingCartItem.quantity + 1,
          price: existingCartItem.price,
        ),
      );
    } else {
      _items.putIfAbsent(
        productId,
        () => CartItem(
          id: DateTime.now().toString(),
          title: title,
          quantity: 1,
          price: price,
        ),
      );
    }
    notifyListeners();
  }

  void removeItem(String productId) {
    _items.remove(productId);
    notifyListeners();
  }

  void clear() {
    _items = {};
    notifyListeners();
  }
}

Answer 1

我认为 prblm 是你有一个代表你的数据模型的 CartItem 类，还有一个 CartItem 是导致 prblm 的小部件。

CartItem 数据模型类

class CartItem {
  final String id;
  final String title;
  final int quantity;
  final double price;

  CartItem({
    required this.id,
    required this.title,
    required this.quantity,
    required this.price,
  });
}

另一个是这个 CartItem Widget，因为您将其返回到 Listview 中

Expanded(
            child: ListView.builder(
              itemBuilder: (context, index) => CartItem(
                id: cart.items.values.toList()[index].id,
                productId: cart.items.keys.toList()[index],
                title: cart.items.values.toList()[index].title,
                quantity: cart.items.values.toList()[index].quantity,
                price: cart.items.values.toList()[index].price,
              ),
              itemCount: cart.itemCount,
            ),
          ),

由于一个是小部件，另一个是对象，因此显示类型错误