二 策略模式

策略模式是一种定义一系列算法的方法，从概念上来看，所有这些算法完成的都是相同的工作，只是实现不同，它可以以相同的方式调用所有的算法，减少了各种算法类与使用算法类之间的耦合

策略模式封装了变化

在实践中，我们发现可以用它来封装几乎任类型的规则，只要在分析过程中听到需要在不同时间应用到不同的业务规则，就考虑使用策略模式来处理这种变化的可能

商场促销例子

现金收费抽象类

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace factoryClass.Strategy
{
    /// <summary>
    /// 现金收费抽象类
    /// </summary>
   public abstract class CashSuper
    {
       /// <summary>
       /// 超类的抽象方法，收取现金
       /// </summary>
        /// <param name="money">参数为原价</param>
        /// <returns>返回为当前价</returns>
       public abstract double acceptCash(double money);
    }
}

正常收费子类

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace factoryClass.Strategy
{
    /// <summary>
    /// 正常收费子类
    /// </summary>
   public class CashNormal:CashSuper
    {
        public override double acceptCash(double money)
        {
            return money;
        }
    }
}

打折收费子类

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace factoryClass.Strategy
{
    /// <summary>
    /// 打折收费子类
    /// </summary>
   public class CashRebate:CashSuper
    {
       private double moneyRebate = 1d;
       public CashRebate(string moneyRebate)
       {
           this.moneyRebate = double.Parse(moneyRebate);
       }
        public override double acceptCash(double money)
        {
            return moneyRebate * money;
        }
    }
}

返利收费子类

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace factoryClass.Strategy
{
    /// <summary>
    /// 返利收费子类
    /// </summary>
  public  class CashReturn:CashSuper
    {
      private double moneyCondition = 0.0d;
      private double moneyReturn = 0.0d;

      public CashReturn(string moneyCondition, string moneyReturn)
      {
          this.moneyCondition = double.Parse(moneyCondition);
          this.moneyReturn = double.Parse(moneyReturn);
      }
        public override double acceptCash(double money)
        {
            double resurt = money;
            if (money >= moneyCondition)
            {
                resurt = money - Math.Floor(money / moneyCondition) * moneyReturn;
            }
            return resurt;
        }
    }
}

CashContext类

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace factoryClass.Strategy
{
   public class CashContext
    {
        CashSuper cs=null;//申明一个CashSuper对象

       /// <summary>
        /// CashContext
       /// </summary>
       /// <param name="type">促销类型</param>
       /// <param name="moneyRebates">折扣</param>
       /// <param name="moneyCondition">满</param>
       /// <param name="moneyReturn">返</param>
        public CashContext(string type, string moneyRebates, string moneyCondition, string moneyReturn)
       {
           switch (type)
           {
               case "0":
                   CashNormal cs0 = new CashNormal();
                   cs = cs0;
                   break;
               case "1":
                   CashRebate cs1 = new CashRebate(moneyRebates);
                   cs = cs1;
                   break;
               case "2":
                   CashReturn cs2 = new CashReturn(moneyCondition, moneyReturn);
                   cs = cs2;
                   break;

           }
       }

       /// <summary>
       /// 根据收费策略不同，获得计算结果
       /// </summary>
       /// <param name="money"></param>
       /// <returns></returns>
       public double GetResult(double money)
       {
           return cs.acceptCash(money);
       }
    }
}

客户端

 protected void btnA_Click(object sender, EventArgs e)
        {
            factoryClass.Strategy.CashContext cashContext = new factoryClass.Strategy.CashContext(this.ddlcu.SelectedValue,this.ddlzhe.SelectedValue,this.txtman.Text,this.txtfan.Text);
            this.txtying.Text = cashContext.GetResult(Convert.ToDouble(this.txtprice.Text)).ToString();
        }