大话设计模式 第二章:策略模式

　　策略模式(strategy)：它定义了算法家族，分别封装起来，让他们之间可以相互替换，此模式让算法的变化，不会影响到试用算法的客户。

　　本文章是的工厂模式和策略模式的结合例子：

1,定义现金抽象类:

    /// <summary>    /// 现金父类    /// </summary>    public abstract class CashSuper    {        /// <summary>        /// 将原价转为返回价        /// </summary>        /// <param name="money">原价</param>           public abstract double acceptCash(double money);    }

2,定义各个算法类,全部继承自现金父类:

    /// <summary>    /// 没有活动的现金类    /// </summary>    public class CashNormal : CashSuper    {        public override double acceptCash(double money)        {            return money;//直接返回原价                   }    }        /// <summary>    /// 打折类    /// </summary>    public class CashRebate : CashSuper    {        private double rebate = 1.0;//打几折        public CashRebate(double rebate)        {            this.rebate = rebate;        }        public override double acceptCash(double money)        {            double result = 0.0;            result = money * rebate;            return result;        }    }    /// <summary>    /// 返回现金类    /// </summary>    public class CashReturn : CashSuper    {        private double moneyCondition;//满多少钱        private double moneyReturn;   //返多少钱        public CashReturn(double moneyCondition, double moneyReturn)        {            this.moneyCondition = moneyCondition;            this.moneyReturn = moneyReturn;        }        public override double acceptCash(double money)        {            double result = 0.0;            result = money - Math.Floor(money / moneyCondition) * moneyReturn;            return result;        }    }

3,定义现金上下文类，决定使用哪一种算法，并实例化哪个算法对象，这是工厂模式与策略模式的结合：

    /// <summary>    /// 现金上下文，选择哪种活动方式    /// </summary>    public class CashContext    {        private CashSuper cash=null;        /// <summary>        /// 根据活动方式返回价格        /// </summary>        /// <param name="type">活动方式(如:打8折)</param>        public CashContext(string type)        {            switch (type)            {                case "正常收费":                    cash = new CashNormal();                    break;                case "打8折":                    cash = new CashRebate(0.8);                    break;                case "满300返100":                    cash = new CashReturn(300, 100);                    break;                default:                    throw new  Exception("没有该活动");            }                           }        /// <summary>        /// 输入原价返回价格        /// </summary>        /// <param name="money">原价</param>            public double GetResult(double money)        {           return cash.acceptCash(money);        }    }

4,客户端界面的设计：

5,客户端后台代码:

    public partial class Form1 : Form    {        public Form1()        {            InitializeComponent();        }        double total = 0.0;        private void buttonOK_Click(object sender, EventArgs e)        {            try            {                double totalPrice = 0.0;                CashContext cashContext = new CashContext(this.comboBox1.Text);                totalPrice = cashContext.GetResult(Convert.ToDouble(textBoxPrice.Text) * Convert.ToDouble(textBoxNum.Text));                string resutl = "单价:" + textBoxPrice.Text + " 数量:" + textBoxNum.Text + " 活动方式:" + comboBox1.SelectedText + " 总价:" + totalPrice.ToString();                listBox1.Items.Add(resutl);                total += totalPrice;                this.labelTotal.Text = total.ToString();            }            catch (Exception ex)            {                MessageBox.Show(ex.Message);                     }                    }        private void Form1_Load(object sender, EventArgs e)        {            string[] type = new string[] { "正常收费", "打8折", "满300返100" };            this.comboBox1.Items.AddRange(type);                 }    }