大话设计模式读书笔记1——简单工厂模式

最近几日，重温了一下《大话设计模式》这本书，当时读的仓促，有很多没有注意的地方，现在仔细翻看起来，发现这值得细细品味的一本书！！

好东西就要记下来！！！

第一章笔记：从一个简单的计算器程序来看简单工厂模式。

变化的地方就要封装，用一个单独的类来做创造实例的过程这就是工厂。

UML图：

    /// <summary>
    /// 运算类
    /// </summary>
    public class Operation
    {
        public double Number1 { get; set; }

        public double Number2 { get; set; }

        public virtual double GetResult()
        {
            double result = 0;
            return result;
        }
    }

    /// <summary>
    /// 加法类
    /// </summary>
    public class OprerationAdd : Operation
    {
        public override double GetResult()
        {
            double reslut = 0;
            reslut = Number1 + Number2;
            return reslut;
        }
    }

    /// <summary>
    /// 减法类
    /// </summary>
    public class OprerationSub : Operation
    {
        public override double GetResult()
        {
            double reslut = 0;
            reslut = Number1 - Number2;
            return reslut;
        }
    }

    /// <summary>
    /// 乘法类
    /// </summary>
    public class OprerationMul : Operation
    {
        public override double GetResult()
        {
            double reslut = 0;
            reslut = Number1 * Number2;
            return reslut;
        }
    }

    /// <summary>
    /// 除法类
    /// </summary>
    public class OprerationDiv : Operation
    {
        public override double GetResult()
        {
            double reslut = 0;
            if (Number2==0)
            {
                throw new Exception("除数不能等于0");
            }
            reslut = Number1 / Number2;
            return reslut;
        }
    }

运算工厂类：

public class OperationFactory
    {
        public static Operation CreateOperate(string oper)
        {
            Operation operation = null;
            switch (oper)
            {
                case "+":
                    operation = new OprerationAdd();
                    break;
                case "-":
                    operation = new OprerationSub();
                    break;
                case "*":
                    operation = new OprerationMul();
                    break;
                case "/":
                    operation = new OprerationDiv();
                    break;
            }
            return operation;
        }
    }

客户端代码：

   public partial class FrmMain : Form
    {
        public FrmMain()
        {
            InitializeComponent();
            this.cbxOper.SelectedIndex = 0;         
        }     
        
        /// <summary>
        /// 运算点击
        /// </summary> 
        private void btnCompute_Click(object sender, EventArgs e)
        {
            double num1 = 0;
            double num2 = 0;
            if (!double.TryParse(this.txtNum1.Text,out num1))
            {
                this.lblInfo.Text = "请输入正确的数字";
                this.txtNum1.Focus();
                return;
            }

            if (!double.TryParse(this.txtNum2.Text, out num2))
            {
                this.lblInfo.Text = "请输入正确的数字";
                this.txtNum2.Focus();
                return;
            }

            Operation operation = null;
            operation = OperationFactory.CreateOperate(this.cbxOper.Text);
            operation.Number1 = num1;
            operation.Number2 = num2;
            double ret = operation.GetResult();
            this.txtResult.Text = ret.ToString();
        }
    }

界面显示：

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