设计模式之策略模式（包含与简单工厂模式的区别，实现了超市结账系统）

今天看了策略模式，不知觉的和前天学的简单工厂模式做了对比，也百度了一些博客，最后的出一个结论，简单工厂模式主要负责初始化各种对象，而策略模式则是更多的对方法进行封装。同一个例子，如果使用简单工厂模式，则是根据需求返回不同的对象，而使用策略模式的话，就是根据需求来返回不同的方法。

下面的例子分别使用简单工厂模式和策略模式和写的超市结账系统，二者功能实现上没有区别。

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 简单工厂模式与策略模式
{
public class Cash
{
double price;
int num;
public double Price
{
get
{
return price;
}
set
{
price = value;
}
}
public int Num
{
get
{
return num;
}
set
{
num = value;
}
}
public virtual string GetCash()
{
return "error";
}
}
public class CashA:Cash
{
public override string GetCash()
{
return (Price * Num).ToString();
}
}
public class CashB : Cash
{
public override string GetCash()
{
return (Price * Num*0.8).ToString();
}
}
public class CashC : Cash
{
public override string GetCash()
{
return (Price * Num * 0.5).ToString();
}
}
public class CashFactory          //工厂类
{
public static Cash GetCashObject(string str)
{
switch (str)
{
case "正常收费": return new CashA();
case "8折收费": return new CashB();
case "5折收费": return new CashC();
default: return new Cash();
}
}
}
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
double total=0;
private void button1_Click(object sender, EventArgs e)
{
double totalPrice;
Cash p = CashFactory.GetCashObject(comboBox1.SelectedItem.ToString());
p.Num = int.Parse(textBox2.Text);
p.Price = double.Parse(textBox1.Text);
totalPrice=double.Parse(p.GetCash());
total+=totalPrice;
listBox1.Items.Add("单价："+textBox1.Text+"数量："+textBox2.Text+"总价为"+totalPrice.ToString());
label4.Text = total.ToString();
}

private void button2_Click(object sender, EventArgs e)
{
textBox1.Text = null;
textBox2.Text = null;
label4.Text = null;
for (int i = 0; i < listBox1.Items.Count;i++ )
{
listBox1.Items.RemoveAt(i);
}
}

private void Form1_Load(object sender, EventArgs e)
{
comboBox1.Items.AddRange(new object[] { "正常收费", "8折收费", "5折收费" });
comboBox1.SelectedIndex = 0;
}
}
}

下面是使用策略模式写的超市结账系统。

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 简单工厂模式与策略模式
{
public class Cash
{
double price;
int num;
public double Price
{
get
{
return price;
}
set
{
price = value;
}
}
public int Num
{
get
{
return num;
}
set
{
num = value;
}
}
public virtual string GetCash()
{
return "error";
}
}
public class CashA:Cash
{
public override string GetCash()
{
return (Price * Num).ToString();
}
}
public class CashB : Cash
{
public override string GetCash()
{
return (Price * Num*0.8).ToString();
}
}
public class CashC : Cash
{
public override string GetCash()
{
return (Price * Num * 0.5).ToString();
}
}
public class CashContext
{
public Cash p;
public CashContext(string str)
{
switch(str)
{
case "正常收费": p = new CashA(); break;
case "8折收费": p = new CashB(); break;
case "5折收费": p = new CashC(); break;
}
}
public string GetResult()
{
return p.GetCash();
}
}
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
double total=0;
private void button1_Click(object sender, EventArgs e)
{
double totalPrice=0;
// Cash p = CashFactory.GetCashObject(comboBox1.SelectedItem.ToString());
CashContext p = new CashContext(comboBox1.SelectedItem.ToString());
p.p.Num = int.Parse(textBox2.Text);
p.p.Price = double.Parse(textBox1.Text);
totalPrice = double.Parse(p.p.GetResult());

total+=totalPrice;
listBox1.Items.Add("单价："+textBox1.Text+"数量："+textBox2.Text+"总价为"+totalPrice.ToString());
label4.Text = total.ToString();
}

private void button2_Click(object sender, EventArgs e)
{
textBox1.Text = null;
textBox2.Text = null;
label4.Text = null;
for (int i = 0; i < listBox1.Items.Count;i++ )
{
listBox1.Items.RemoveAt(i);
}
}

private void Form1_Load(object sender, EventArgs e)
{
comboBox1.Items.AddRange(new object[] { "正常收费", "8折收费", "5折收费" });
comboBox1.SelectedIndex = 0;
}
}
}

求大神点拨，感觉用起来区别不大，二者还可以相互融合使用。