public class ShopCart    {        private string UserId;        public List<CartItem> CartItems { get; set; } = new List<CartItem>();        private ShopCart()        {        }        public ShopCart(string userId)        {            this.UserId = userId;            InitCart();        }        #region 初始化购物车        private void InitCart()        {            CartItems = new ShopCarBll().GetListByUserId(UserId) ?? (List<CartItem>)new List<CartItem>();        }        #endregion        #region 对购物车进行操作        /// <summary>        /// 添加商品        /// </summary>        /// <param name="productId"></param>        /// <param name="count"></param>        /// <returns></returns>        public bool AddProduct(int productId, int count)        {            var productModel = new ProductBll().GetModel(productId);            if (productModel != null)            {                if (CartItems.Any(x => x.ProductId == productId))                {                    return ModifyCount(productId, count);                }                else                {                    //更新购物车到数据库中做持外化                    if (new ShopCarBll().Add(UserId, productId, count))                    {                        CartItems.Add(new CartItem(productModel.Id, productModel.Price, count));                        return true;                    }                }            }            return false;        }        /// <summary>        /// 修改商品数量        /// </summary>        /// <param name="productId"></param>        /// <param name="count"></param>        /// <returns></returns>        public bool ModifyCount(int productId, int count)        {            var item = CartItems.FirstOrDefault(x => x.ProductId == productId);            if (item != null)            {                if (new ShopCarBll().Mobify(UserId, productId, count))                {                    //更新到数据库中                    item.Count = count;                    return true;                }            }            return false;        }        /// <summary>        /// 移除商品        /// </summary>        /// <param name="productId"></param>        /// <returns></returns>        public bool RemoveProduct(int productId)        {            var item = CartItems.FirstOrDefault(x => x.ProductId == productId);            if (item != null)            {                if (new ShopCarBll().Remove(UserId, productId))                {                    //更新到数据库中                    CartItems.Remove(item);                    return true;                }            }            return false;        }        #endregion        /// <summary>        /// 获取购物车总价        /// </summary>        /// <returns></returns>        public decimal GetSumFee()        {            return CartItems.Sum(x => x.Count * x.Count);        }    }    public class CartItem    {        public int ProductId { get; set; }        public int Count { get; set; }        public decimal Price { get; set; }        public CartItem(int productId, decimal price, int count)        {            this.ProductId = productId;            this.Count = count;            this.Price = price;        }    }
接着写测试类

 public class testCart    {        public void Test()        {            string userId = "123123123";            ShopCart myCart = new ShopCart(userId);            myCart.AddProduct(1001, 1);            myCart.AddProduct(1002, 3);            myCart.AddProduct(1003, 2);            myCart.ModifyCount(1002, 5);//修改购物车数量            myCart.RemoveProduct(1003);//删除购物车商品            decimal sumFee = myCart.GetSumFee();//获取所有购物车金额        }    }

完工