flutter - 如何添加我购物车中所有商品的总数而不是商品*数量，还添加运费和折扣以使其总计？

Question

我正在尝试添加我们在每件商品的数量 * 价格之后获得的商品总量，并在其中添加运费使其总计，然后我们继续结帐。这是我的购物车模型

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

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

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

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

  int get itemCount {
    return _items.length;
  }

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

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

  void removeSingleItem(String id) {
    if (!_items.containsKey(id)) {
      return;
    }
    if (_items[id].quantity > 1) {
      _items.update(
          id,
          (existingCartItem) => CartItem(
              id: DateTime.now().toString(),
              name: existingCartItem.name,
              quantity: existingCartItem.quantity - 1,
              price: existingCartItem.price));
    }
    notifyListeners();
  }

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

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

这是我的购物车屏幕代码；

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

  @override
  Widget build(BuildContext context) {
    final cart = Provider.of<Cart>(context);
    return Scaffold(
      appBar: AppBar(
        title: Text(
          'My Cart',
          style: TextStyle(fontSize: 30, color: Theme.of(context).accentColor),
        ),
      ),
      body: Column(
        children: <Widget>[
          Expanded(
            child: ListView.builder(
                itemCount: cart.items.length,
                itemBuilder: (ctx, i) => CartPdt(
                    cart.items.values.toList()[i].id,
                    cart.items.keys.toList()[i],
                    cart.items.values.toList()[i].price,
                    cart.items.values.toList()[i].quantity,
                    cart.items.values.toList()[i].name)),
          ),
          CheckoutButton(
            cart: cart,
          ),
         
        ],
      ),
    );
  }
}

我只是想添加总金额并添加运费以使其总计并低于结帐按钮

标签： flutter