EPower2002示例:运用"工厂方法"设计类

1.新建一类库工程,命名为"VBNETDesignMode.vb"
2.将Class1.vb删除
3.在此工程中添加类,命名为"FactoryMethod.vb"
4.在"FactoryMethod.vb"中添加产品类"Product".
  (1)添加三个私有成员变量:mID,mName,mCreaDate
  (2)添加三个公有属性:ID,Name,CreaDate
***********************************************
FactoryMethod.vb代码如下:
***********************************************
Public Class Product    '产品
    '定义私有成员变量
    Private mID As Integer
    Private mName As String
    Private mCreaDate As DateTime
    '定义属性
    Public Property ID() As Integer
        Get
            Return mID
        End Get
        Set(ByVal Value As Integer)
            mID = Value
        End Set
    End Property
    Public Property Name() As String
        Get
            Return mName
        End Get
        Set(ByVal Value As String)
            mName = Value
        End Set
    End Property
    Public Property CreaDate() As DateTime
        Get
            Return mCreaDate
        End Get
        Set(ByVal Value As DateTime)
            mCreaDate = Value
        End Set
    End Property

    '以下还可定义其它属性
    '以下还可定义更多方法
    '以下还可定义更多事件
End Class

5.再添加一类,命名为"Factory.vb"
6.在其类中,用Overridable关键字定义CreateProduct方法,方法将返回一个Product类的实例.
7.在CreateProduct函数体中初始化Product类.在这里,为演示方便,我们将此产品编号ID定为99999,产品名称Name定为"DreamFactoryNO.1",出产日期为date.now

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Factory.vb代码如下:
**********************************
Public Class Factory    '工厂
    '用Overridable关键字定义CreateProduct方法,该方法返回一个Product类的实例
    '由于它有Overridable关键字,其子类可用Overrides关键字覆盖。
    Public Overridable Function CreateProduct() As Product
        Dim NewProduct As New Product()
        '进行产品类的初始化工作
        NewProduct.ID = 99999
        NewProduct.Name = "DreamFactoryNO.1"
        NewProduct.CreaDate = Date.Now
        Return NewProduct
    End Function
End Class

8.接下来,我们要在该解决方案中添加一"window应用程序"项目,将该项目命名为"Test"
一般来说,最好将该测试工程保存在该类的文件夹内.

9.将VS默认生成的form1.vb更名为"frmFactory.vb",最好也代码视图中的"public Class Form1()"改为"public Class frmFactory()"
代码如下:
Public Class frmFactory
    Inherits System.Windows.Forms.Form
    #Region " Windows 窗体设计器生成的代码 "
    注:其中代码已省略
    #End Region
End Class

10.添加对"VBNETDesignMode"项目的引用,并导入VBNETDesignMode名称空间.
Imports VBNETDesignMode

11.添加一个名为"NewFactory"的新类,我们将让此类继承Factory类.继承是通过Inherits关键字实现的.
Inherits VBNETDesignMode.Factory

12.由于我们要对产品进行新的初始化操作,因此,我们将要覆盖CreateProduct方法.
前面我们说过,该方法之所以可以覆盖,是因为它是被Overridable关键字来声明的.
Public Class NewFactory
    Inherits VBNETDesignMode.Factory
    Public Overrides Function CreateProduct() As Product
        Dim NewProduct As New Product()
        '进行产品类的初始化工作
        NewProduct.ID = 88888
        NewProduct.Name = "DreamFactoryNO.2"
        NewProduct.CreaDate = Date.Now
        Return NewProduct
    End Function
End Class

13.最后,我们在窗体的Load中来分别测试:

    Private Sub frmFactory_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        Dim OldPro As New Product()
        Dim OldFac As New Factory()
        OldPro = OldFac.CreateProduct
        Debug.WriteLine("********旧产品信息**********")
        Debug.WriteLine("        ID:" & OldPro.ID)
        Debug.WriteLine("      Name:" & OldPro.Name)
        Debug.WriteLine("  CreaDate:" & OldPro.CreaDate)

        Dim NewPro As New Product()
        Dim NewFac As New NewFactory()
        NewPro = NewFac.CreateProduct
        Debug.WriteLine("********新产品信息**********")
        Debug.WriteLine("        ID:" & NewPro.ID)
        Debug.WriteLine("      Name:" & NewPro.Name)
        Debug.WriteLine("  CreaDate:" & NewPro.CreaDate)
    End Sub

小结:
以上代码虽无什么实用价值,但是实现这些代码的设计思想却是很有实用价值的,当你真正理解"工厂方法"的设计模式后,你可以开发出效率更高更专业的东西来的.