二、策略模式之商场促销计价器

1、创建一个窗体项目，窗体内控件如图所示：

2、相应的类如下

using System;

namespace 商场促销_策略模式实现
{
    // 现金收取超类的抽象方法，收取现金，参数为原价，返回为当前价
    abstract class CashSuper
    {
        public abstract double acceptCash(double money);
    }
    //正常收费，原价返回
    class CashNormal : CashSuper
    {
        public override double acceptCash(double money)
        {
            return money;
        }
    }
    //打折收费类，初始化时必须输入折扣率，如八折 0.8
    class CashRebate : CashSuper
    {
        private double moneyRebate = 1d;
        public CashRebate(string moneyRebate)
        {
            this.moneyRebate = double.Parse(moneyRebate);
        }
        public override double acceptCash(double money)
        {
            return money * moneyRebate;
        }
    }
    //返利收费类，初始化时必须要输入返利条件和返利值，如满300返100
    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 result = money;
            if (money >= moneyCondition)   //若满足返利条件，则减去返利值
                result = money - Math.Floor(money / moneyCondition) * moneyReturn;

            return result;
        }
    }

    class CashContext
    {
        CashSuper cs;   //声明一个CashSuper
        //通过构造方法，传入具体的收费策略
        public CashContext(string type) //参数type为字符串，表示收费策略
        {
            switch (type)   //将实例化具体策略的过程由客户端转移到Context类中，即简单工厂的应用
            {
                case "正常收费":
                    CashNormal cs0 = new CashNormal();
                    cs = cs0;
                    break;
                case "满300返100":
                    CashReturn cs1 = new CashReturn("300","100");
                    cs = cs1;
                    break;
                case "打八折":
                    CashRebate cs2 = new CashRebate("0.8");
                    cs = cs2;
                    break;
            }
        }
        //根据收费策略不同，获得计算结果
        public double GetResult(double money)
        {
            return cs.acceptCash(money);
        }

    }
}

3、窗体控件相关操作代码

using System;
using System.Windows.Forms;

namespace 商场促销_策略模式实现
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        double total = 0.0d;    //用于总计

        private void btnOk_Click(object sender, EventArgs e)
        {
            string strCashAccept = cbxType.Text;    //声明计价类型
            CashContext cc = new CashContext(cbxType.Text); //将选定的计价类型用于初始化对应的计价策略
            double totalPrice = 0d;
            totalPrice = cc.GetResult(Convert.ToDouble(txtPrice.Text) * Convert.ToDouble(txtTotal.Text));   //根据计价策略计算得到结果
            total = total + totalPrice;
            lbxList.Items.Add("单价：" + txtPrice.Text + " 数量：" + txtTotal.Text + " " +    //显示计算得到的结果
                cbxType.SelectedItem + "	合计：" + totalPrice.ToString());
            lblResult.Text = total.ToString();
        }

        private void btnClear_Click(object sender, EventArgs e)
        {
            txtPrice.Text = null;   //清空显示结果
            txtTotal.Text = null;
            lbxList.Items.Clear();
            lblResult.Text = null;
            total = 0d;
        }
    }
}

注：本文内容是《大话设计模式》一书阅读过程复写代码！