设计模式-策略模式C#版

using System; using System.Collections.Generic; using System.Linq; using System.Text;  namespace DomainModel.Model {     /// <summary>     /// 打折策略     /// </summary>     public interface IDiscountStrategy     {         decimal Apply(decimal originalPrice);     }      public class Price     {         private IDiscountStrategy _discountStrategy;         private decimal _salePrice;          public Price(decimal salePrice, IDiscountStrategy discountStrategy)         {             this._salePrice = salePrice;             this._discountStrategy = discountStrategy;         }         /// <summary>         /// 应用策略         /// </summary>         /// <param name="discountStrategy"></param>         public void SetDiscountStrategy(IDiscountStrategy discountStrategy)         {             this._discountStrategy = discountStrategy;         }         /// <summary>         /// 返回打折后的价格         /// </summary>         public decimal SalePrice         {              get             {                 return this._discountStrategy.Apply(this._salePrice);             }         }      }      public class Product     {          public int Id { get; set; }          public string Name { get; set; }          public Price Price { get; set; }     }     public enum CustomerType     {         /// <summary>         ///  不打折        /// </summary>         General = 0,         /// <summary>         ///  6折        /// </summary>         Trade = 1     }     public class NullDiscountStrategy : IDiscountStrategy     {          public decimal Apply(decimal originalPrice)         {             return originalPrice;         }     }     public class TradeDiscountStrategy : IDiscountStrategy     {         public decimal Apply(decimal originalPrice)         {             return originalPrice * 0.6m;         }     }     /// <summary>     /// 折扣策略工厂     /// </summary>     public sealed class DiscountStrategyFactory     {          public static IDiscountStrategy GetDiscountStrategy(CustomerType customerType)         {             switch (customerType)             {                 case CustomerType.General:                     return new NullDiscountStrategy();                 default:                     return new TradeDiscountStrategy();             }         }     }     public interface IProductRepository     {         IList<Product> Find();     }      public static class ProductListExtensions     {         public static void ApplyDiscount(this IList<Product> products, IDiscountStrategy discountStrategy)         {             foreach (var p in products)             {                 p.Price.SetDiscountStrategy(discountStrategy);             }         }     }      public class ProductRepository:IProductRepository      {         public IList<Product> Find()         {             return new List<Product>();         }     }     public class ProductService     {         private IProductRepository _productRepository;         public ProductService()         {             this._productRepository = new ProductRepository();         }         public ProductService(IProductRepository productRepository)         {             this._productRepository = productRepository;         }          public IList<Product> Find(CustomerType customerType)         {             var discountStrategy = DiscountStrategyFactory.GetDiscountStrategy(customerType);             var products = this._productRepository.Find();             products.ApplyDiscount(discountStrategy);             return products;         }     }      public class Client     {         private CustomerType _customerType = CustomerType.Trade;                  public void FindProducts()         {             var service = new ProductService();             var products = service.Find(this._customerType);         }     } }