设计模式：工厂方法模式（Factory Method）

定义：定义一个用于创建对象的接口，让子类决定实例化哪一个类。

工厂方法使一个类的实例化延迟到其子类。

结构图：

示例：

HTML代码：

<html xmlns="http://www.w3.org/1999/xhtml">

<head runat="server">

    <title></title>

</head>

<body>

    <form id="form1" runat="server">

    <div>

        <asp:TextBox runat="server" ID="txtNumberA"></asp:TextBox>

        <asp:DropDownList runat="server" ID="ddlType">

            <asp:ListItem Selected="True">+</asp:ListItem>

            <asp:ListItem>-</asp:ListItem>

            <asp:ListItem>*</asp:ListItem>

            <asp:ListItem>/</asp:ListItem>

        </asp:DropDownList>

        <asp:TextBox runat="server" ID="txtNumberB"></asp:TextBox>

        =

        <asp:TextBox runat="server" ID="txtResult"></asp:TextBox>

        <asp:Button runat="server" ID="btnCalculate" Text="计算" OnClick="btnCalculate_Click" />

        <asp:Label runat="server" ID="lblMsg"></asp:Label>

    </div>

    </form>

</body>

</html>

IFactory.cs:
interface IFactory
    {
        Operation CreateOpertion();
    }

AddFactory.cs:

public class AddFactory : IFactory
    {
        public Operation CreateOpertion()
        {
            return new OperateAdd();
        }
    }

SubFactory.cs:

public class SubFactory : IFactory
    {
        public Operation CreateOpertion()
        {
            return new OperateSub();
        }
    }

MulFactory.cs:

public class MulFactory : IFactory
    {
        public Operation CreateOpertion()
        {
            return new OperateMul();
        }
    }

DivFactory.cs:

public class DivFactory : IFactory
    {
        public Operation CreateOpertion()
        {
            return new OperateDiv();
        }
    }

Operation.cs:

 public class Operation

    {

        public int NumberA { get; set; }

        public int NumberB { get; set; }

        public virtual int GetResult()

        {

            return ;

        }

    }

OperateAdd.cs:

 public class OperateAdd : Operation

    {

        public override int GetResult()

        {

            return NumberA + NumberB;

        }

    }

OperateSub.cs:

public class OperateSub : Operation

    {

        public override int GetResult()

        {

            return NumberA - NumberB;

        }

    }

OperateMul.cs:

 public class OperateMul : Operation

    {

        public override int GetResult()

        {

            return NumberA * NumberB;

        }

    }

OperateDiv.cs:

 public class OperateDiv : Operation

    {

        public override int GetResult()

        {

            int result = ;

            if (NumberB == )

                throw new Exception("被除数为0！");

            result = NumberA / NumberB;

            return result;

        }

    }

客户端代码：

  protected void btnCalculate_Click(object sender, EventArgs e)

        {

            IFactory factory = null;

            string type = ddlType.SelectedValue;

            switch (type)

            {

                case "+":

                    factory = new AddFactory();

                    break;

                case "-":

                    factory = new SubFactory();

                    break;

                case "*":

                    factory = new MulFactory();

                    break;

                case "/":

                    factory = new DivFactory();

                    break;

            }

            try

            {

                Operation operation = factory.CreateOpertion();

                operation.NumberA = Convert.ToInt32(txtNumberA.Text);

                operation.NumberB = Convert.ToInt32(txtNumberB.Text);

                txtResult.Text = operation.GetResult().ToString();

            }

            catch (Exception ex)

            {

                lblMsg.Text = ex.Message;

            }

        }

简单工厂模式和工厂方法模式比较：

简单工厂：最大优点在于工厂类中包含了必要的逻辑判断，根据客户端的选择条件动态实例化相应的类，对于客户端来说，

去除了与具体产品的依赖。（违反了开闭原则）

工厂方法：将必要的判断逻辑放在客户端，这样在增加新的产品类时只需要增加相应的工厂类，而不需要修改原来的类，遵

守了开闭原则。

巴特西

设计模式：工厂方法模式（Factory Method）

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