设计模式之策略模式

UML:

CashSuper(父类)

 /// <summary>
    /// 2014-05-21
    /// 超市商品收费
    /// </summary>
    public abstract class CashSuper
    {
        public abstract double AcceptCash(double money);
    }

子类：

 /// <summary>
    /// 普通收费
    /// </summary>
    public class NormalCashSuper : CashSuper
    {
        public override double AcceptCash(double money)
        {
            return money;
        }
    }

 /// <summary>
    /// 打折收费
    /// </summary>
    public class RebateCashSuper : CashSuper
    {
        public double MoneyRebate
        {
            get;
            set;
        }
        public RebateCashSuper(double moneyRebate)
        {
            this.MoneyRebate = moneyRebate;
        }
        public override double AcceptCash(double money)
        {
            return this.MoneyRebate * money ;
        }
    }

 /// <summary>
    /// 返利收费
    /// </summary>
    public class ReturnCashSuper : CashSuper
    {
        /// <summary>
        /// 返利金额条件
        /// </summary>
        public double MoneyCondition
        {
            get;
            set;
        }
        /// <summary>
        /// 返利金额
        /// </summary>
        public double ReturnMoney
        {
            get;
            set;
        }
        public override double AcceptCash(double money)
        {
            if (money >= this.MoneyCondition)
            {
                return money  - this.ReturnMoney;
            }
            else
            {
                return money;
            }
        }
    }

策略类：

 public class CashContext
    {
        private CashSuper cashSuper = null;
        public CashContext(CashSuper cs)
        {
            this.cashSuper = cs;
        }
      

        public double GetResult(double money)
        {
           double returnMoney = this.cashSuper.AcceptCash(money);
           return returnMoney;
        }  
        
    
    }

页面代码：

protected void btnStrategy_Click(object sender, EventArgs e)
        {
            CashContext cc = null;
            int intType = int.Parse(this.DropDownList1.SelectedValue.Trim());
            double dbRebate = double.Parse(this.txtRebate.Text.Trim());
            double dbConditonMoney = double.Parse(this.txtCondition.Text.Trim());
            double dbReturnMoney = double.Parse(this.txtReturnMoney.Text.Trim());
            double dbMoney = double.Parse(this.txtMoney.Text.Trim());  
            switch (intType)
            { 
                case 1:
                    cc = new CashContext(new NormalCashSuper());
                    break;
                case 2:
                    RebateCashSuper rcs = new RebateCashSuper(dbRebate);
                    cc = new CashContext(rcs);
                    break;
                case 3:
                    ReturnCashSuper recs = new ReturnCashSuper();
                    recs.MoneyCondition = dbConditonMoney;
                    recs.ReturnMoney = dbReturnMoney;
                    cc = new CashContext(recs);
                    break;
            }
            Response.Write(cc.GetResult(dbMoney).ToString());  
 
        }

问题

1：书中有提到将页面上的条件判断代码放到策略类中，那折扣，返利等数据如何传递？

　　如下：public CashContext(int intType,.....?)
        {
            switch(inttype)

　　　　　　{

　　　　　　　　case 1:

　　　　　　　　　　new NormalCashSuper();

　　　　　　　　　　break;

　　　　　　}
        }

2:代码中的money指的是计算后的总价。如业务变化，需增加买5退一的业务（即买5个只算4个的价格），如何更改代码？

   此业务和以上三种业务的关系是什么（兄弟OR没关系）？

总结：

1：页面只访问了CashContext类，算法和客户端分离了。

2：算法可以单独进行单元测试，互相不受影响。

3：客户端代码简单了。