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);         
        }
    }