设计模式（1）--简单工厂模式

采用计算器的实例来说明。

到底实例化谁，将来会不会增加实例化得对象，比如增加开根运算，这是很容易变化的地方（需要经常改动），应该用一个单独的类来做这个创造实例的过程，这就是工厂。利用工厂产生的是各种各样的对象。但都有一个共同的父类，这样利用多态的特性，调用父类的方法，会执行被子类覆盖的同名方法。

核心代码（业务代码）（Operation.cs）：

using System;
using System.Collections.Generic;
using System.Text;

namespace OperationLibrary
{
    /// <summary>
    /// 运算类
    /// </summary>
    public class Operation
    {
        private double _numberA = 0;
        private double _numberB = 0;

        /// <summary>
        /// 数字A
        /// </summary>
        public double NumberA
        {
            get
            {
                return _numberA;
            }
            set
            {
                _numberA = value;
            }
        }

        /// <summary>
        /// 数字B
        /// </summary>
        public double NumberB
        {
            get
            {
                return _numberB;
            }
            set
            {
                _numberB = value;
            }
        }

        /// <summary>
        /// 得到运算结果
        /// </summary>
        /// <returns></returns>
        public virtual double GetResult()
        {
            double result = 0;
            return result;
        }

        /// <summary>
        /// 检查输入的字符串是否准确
        /// </summary>
        /// <param name="currentNumber"></param>
        /// <param name="inputString"></param>
        /// <returns></returns>
        public static string checkNumberInput(string currentNumber, string inputString)
        {
            string result = "";
            if (inputString == ".")
            {
                if (currentNumber.IndexOf(".") < 0)
                {
                    if (currentNumber.Length == 0)
                        result = "0" + inputString;
                    else
                        result = currentNumber + inputString;
                }
            }
            else if (currentNumber == "0")
            {
                result = inputString;
            }
            else
            {
                result = currentNumber + inputString;
            }

            return result;
        }


    }

    /// <summary>
    /// 加法类
    /// </summary>
    class OperationAdd : Operation
    {
        public override double GetResult()
        {
            double result = 0;
            result = NumberA + NumberB;
            return result;
        }
    }

    /// <summary>
    /// 减法类
    /// </summary>
    class OperationSub : Operation
    {
        public override double GetResult()
        {
            double result = 0;
            result = NumberA - NumberB;
            return result;
        }
    }

    /// <summary>
    /// 乘法类
    /// </summary>
    class OperationMul : Operation
    {
        public override double GetResult()
        {
            double result = 0;
            result = NumberA * NumberB;
            return result;
        }
    }

    /// <summary>
    /// 除法类
    /// </summary>
    class OperationDiv : Operation
    {
        public override double GetResult()
        {
            double result = 0;
            if (NumberB == 0)
                throw new Exception("除数不能为0。");
            result = NumberA / NumberB;
            return result;
        }
    }

    /// <summary>
    /// 平方类
    /// </summary>
    class OperationSqr : Operation
    {
        public override double GetResult()
        {
            double result = 0;
            result = NumberB * NumberB;
            return result;
        }
    }

    /// <summary>
    /// 平方根类
    /// </summary>
    class OperationSqrt : Operation
    {
        public override double GetResult()
        {
            double result = 0;
            if (NumberB < 0)
                throw new Exception("负数不能开平方根。");
            result = Math.Sqrt(NumberB);
            return result;
        }
    }

    /// <summary>
    /// 相反数类
    /// </summary>
    class OperationReverse : Operation
    {
        public override double GetResult()
        {
            double result = 0;
            result = -NumberB;
            return result;
        }
    }

    /// <summary>
    /// 运算类工厂
    /// </summary>
public class OperationFactory
{
    public static Operation createOperate(string operate)
    {
        Operation oper = null;
        switch (operate)
        {
            case "+":
                {
                    oper = new OperationAdd();
                    break;
                }
            case "-":
                {
                    oper = new OperationSub();
                    break;
                }
            case "*":
                {
                    oper = new OperationMul();
                    break;
                }
            case "/":
                {
                    oper = new OperationDiv();
                    break;
                }
            case "sqr":
                {
                    oper = new OperationSqr();
                    break;
                }
            case "sqrt":
                {
                    oper = new OperationSqrt();
                    break;
                }
            case "+/-":
                {
                    oper = new OperationReverse();
                    break;
                }
        }

        return oper;
    }
}
} 

具体界面可根据使用要求的不同进行编写：

本例采用两种不同的方案来完成：

1，Console版本

代码：

using System;
using System.Collections.Generic;
using System.Text;
using OperationLibrary;

namespace 计算器控制台
{

    class Program
    {
        static void Main(string[] args)
        {
            try
            {
                Console.Write("请输入数字A：");
                string strNumberA = Console.ReadLine();
                Console.Write("请选择运算符号(+、-、*、/)：");
                string strOperate = Console.ReadLine();
                Console.Write("请输入数字B：");
                string strNumberB = Console.ReadLine();
                string strResult = "";

                Operation oper;
                oper = OperationFactory.createOperate(strOperate);
                oper.NumberA = Convert.ToDouble(strNumberA);
                oper.NumberB = Convert.ToDouble(strNumberB);
                strResult = oper.GetResult().ToString();

                Console.WriteLine("结果是：" + strResult);

                Console.ReadLine();


            }
            catch (Exception ex)
            {
                Console.WriteLine("您的输入有错：" + ex.Message);
            }
        }
    }
}

运行结果：

 

２，GUI 版本

代码：

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using OperationLibrary;

namespace 计算器
{
    /// <summary>
    /// 面向对象编程
    /// 1、加运算类
    /// 2、加运算子类
    /// 3、加运算类工厂
    /// 4、更改Form1
    public partial class Form1 : Form
    {
        bool bOperate = false;
        Operation oper;

        public Form1()
        {
            InitializeComponent();
        }

        private void button0_Click(object sender, EventArgs e)
        {
            if (bOperate)
            {
                txtShow.Text = "";
                bOperate = false;
            }
            
            string number = ((Button)sender).Text;

            txtShow.Text = Operation.checkNumberInput(txtShow.Text, number);
            
        }

        private void buttonClear_Click(object sender, EventArgs e)
        {
            txtShow.Text = "";
        }

        private void buttonAdd_Click(object sender, EventArgs e)
        {
            if (txtShow.Text != "")
            {
                oper = OperationFactory.createOperate(((Button)sender).Text);
                
                oper.NumberA = Convert.ToDouble(txtShow.Text);
                
                bOperate = true;
            }
        }

        private void buttonEqual_Click(object sender, EventArgs e)
        {
            if (txtShow.Text != "")
            {
                if (((Button)sender).Text != "=")
                {
                    oper = OperationFactory.createOperate(((Button)sender).Text);
                }
                
                oper.NumberB = Convert.ToDouble(txtShow.Text);

                
                txtShow.Text = oper.GetResult().ToString();
                bOperate = true;
            }
        }

 
    }
}

 

运行结果：

UML结构图：