在博客文章中，我们提到的简单工厂模式。然而，GoF摘要23设计模式，而不是她的影子，严厉格感，简单工厂模式是不是一种设计模式，合设计模式的开放—封闭原则，即软件实体如类、模块等应该能够扩展，可是不可改动。对于设计模式的设计原则，将在下一篇博文中介绍。这里我们先来看一个样例：

周所周知，超市收银系统都具有计费功能，那么要你做一个可以依据输入的商品单位价格和数量，以及计费方式进行计算的模块，你怎样做？计费方式也就是打不打折，有没有返利优惠等等。那么我们先用简单工厂模式去实现一下。

简单工厂实现

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;namespace 商场收银软件
{public partial class Form1 : Form{public Form1(){InitializeComponent();}double total = 0.0d;private void textBox1_TextChanged(object sender, EventArgs e){}private void label5_Click(object sender, EventArgs e){}private void Form1_Load(object sender, EventArgs e){cbxType.Items.AddRange(new object[] { "正常收费", "满300返100", "打8折" });cbxType .SelectedIndex =0;}private void buttonOK_Click(object sender, EventArgs e){CashSuper csuper = CashFactory.createCashAccept(cbxType.SelectedItem.ToString());double totalPrices = 0d;totalPrices = csuper.acceptCash(Convert.ToDouble(txtPrice.Text) * Convert.ToDouble(txtNum.Text));total = total + totalPrices;lbxList.Items.Add("单位价格：" + txtPrice.Text + "数量：" + txtNum.Text +"计费方式："+ cbxType.SelectedItem + "合计：" + totalPrices.ToString());lblResult.Text = total.ToString();}private void button2_Click(object sender, EventArgs e){txtNum.Text = "";txtPrice.Text = "";lbxList.Items.Clear();lblResult.Text = "0.00";}}//现金收费抽象类abstract class CashSuper{public abstract double acceptCash(double money);}//正常收费子类class CashNormal : CashSuper{public override double acceptCash(double money){return money;}}//打折收费子类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;}}//返利收费子类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)result = money - Math.Floor(money / moneyCondition) * moneyReturn;return result;}}//现金收费工厂类class CashFactory{public static CashSuper createCashAccept(string type){CashSuper cs = null;switch (type){case "正常收费":cs = new CashNormal();break;case "满300返100":CashReturn cr1 = new CashReturn("300", "100");cs = cr1;break;case "打8折":CashRebate cr2 = new CashRebate("0.8");cs = cr2;break;}return cs;}}
}

我们看到，这样的方案的特点就是将计费方式的实例化放到了工厂里。从而在须要加入新的计费方式的时候，仅仅需在工厂里加一下条件。完了再设计一个对应的类就可以。

可是这样做相同也破坏了开放—封闭原则，每一次的扩展都要大动干戈，实在是不好，不好。面对算法的时常变动。怎样应对？以下我们用还有一种方式试试：

策略模式实现

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;namespace 商场收银软件
{public partial class Form1 : Form{public Form1(){InitializeComponent();}double total = 0.0d;private void textBox1_TextChanged(object sender, EventArgs e){}private void label5_Click(object sender, EventArgs e){}private void Form1_Load(object sender, EventArgs e){cbxType.Items.AddRange(new object[] { "正常收费", "满300返100", "打8折" });cbxType .SelectedIndex =0;}private void buttonOK_Click(object sender, EventArgs e){//简单工厂模式的client代码//CashSuper csuper = CashFactory.createCashAccept(cbxType.SelectedItem.ToString());//double totalPrices = 0d;//totalPrices = csuper.acceptCash(Convert.ToDouble(txtPrice.Text) * Convert.ToDouble(txtNum.Text));//total = total + totalPrices;//lbxList.Items.Add("单位价格：" + txtPrice.Text + "数量：" + txtNum.Text +"计费方式："+ cbxType.SelectedItem + "合计：" + totalPrices.ToString());//lblResult.Text = total.ToString();//策略模式的client代码CashContext cc = null;switch (cbxType.SelectedItem.ToString()){case "正常收费":cc = new CashContext(new CashNormal());break;case "满300返100":cc = new CashContext(new CashReturn("300", "100"));break;case "打8折":cc = new CashContext(new CashRebate("0.8"));break;}double totalPrices = 0d;totalPrices = cc.GetResult(Convert.ToDouble(txtPrice.Text) * Convert.ToDouble(txtNum.Text));total = total + totalPrices;lbxList.Items.Add("单位价格：" + txtPrice.Text + "数量：" + txtNum.Text + "计费方式：" + cbxType.SelectedItem + "合计：" + totalPrices.ToString());lblResult.Text = total.ToString();}private void button2_Click(object sender, EventArgs e){txtNum.Text = "";txtPrice.Text = "";lbxList.Items.Clear();lblResult.Text = "0.00";}}//现金收费抽象类abstract class CashSuper{public abstract double acceptCash(double money);}//正常收费子类class CashNormal : CashSuper{public override double acceptCash(double money){return money;}}//打折收费子类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;}}//返利收费子类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)result = money - Math.Floor(money / moneyCondition) * moneyReturn;return result;}}//现金收费工厂类//class CashFactory//{//    public static CashSuper createCashAccept(string type)//    {//        CashSuper cs = null;//        switch (type)//        {//            case "正常收费"://                cs = new CashNormal();//                break;//            case "满300返100"://                CashReturn cr1 = new CashReturn("300", "100");//                cs = cr1;//                break;//            case "打8折"://                CashRebate cr2 = new CashRebate("0.8");//                cs = cr2;//                break;//        }//        return cs;//    }//}//CashContext类class CashContext{private CashSuper cs;public CashContext(CashSuper csuper){this.cs = csuper;}public double GetResult(double money){return cs.acceptCash(money);}}
}

对照两个方案，我们能够看到不同之处就是策略模式将工厂类撤了。取而代之的是CashContext类，然而又将实现哪一个算法的推断交给了client，这样client承担的责任又大了，不好。不好……

怎么办？要不将简单工厂和策略模式混搭？试试看。对于他们的结合。仅仅需将CashContext类改造一下就可以，例如以下：

 //改造后的CashContext类class CashContext{CashSuper cs = null ;public CashContext(string type){switch (type){case "正常收费":CashNormal cs0 = new CashNormal();cs = cs0;break;case "满300返100":CashReturn cr1 = new CashReturn("300", "100");cs = cr1;break;case "打8折":CashRebate cr2 = new CashRebate("0.8");cs = cr2;break;}}public double GetResult(double money){return cs.acceptCash(money);}}

这样一来，client的代码就要简单的多了，简单工厂模式须要让client和两个类CashSuper和CashFactory打交道，而策略模式与简单工厂结合后的使用方法，client就仅仅需和CashContext打交道就可完毕对应的功能，减少了耦合性。

我们再回过头去看策略模式的定义：

策略模式：定义了算法家族，分别封装起来，让它们之间能够相互替代，此模式让算法的变化，不会影响到使用此算法的客户。