'Singleton模式:一个类只会创建一个实例。
Module Module1

    Sub Main()
        Dim In1 As Singleton = Singleton.Intance
        In1.Name = "李小龙"
        Dim In2 As Singleton = Singleton.Intance

        System.Console.WriteLine(Object.ReferenceEquals(In1, In2) = True)
        System.Console.WriteLine(In1.Name)
        System.Console.WriteLine(In2.Name)
        System.Console.ReadLine()

    End Sub

End Module

Public Class Singleton

    Private Shared m_Intance As Singleton
    Private Shared m_Mutex As New System.Threading.Mutex '同步基元也可用于进程间同步
    Private m_Name As String
    Private Sub New()

    End Sub

    Public Shared Function Intance() As Singleton
        m_Mutex.WaitOne() '当在派生类中重写时，阻塞当前线程，直到当前的 System.Threading.WaitHandle 收到信号

        Try
            If m_Intance Is Nothing Then
                m_Intance = New Singleton   '释放 System.Threading.Mutex 一次
            End If
        Finally
            m_Mutex.ReleaseMutex()
        End Try
        Return m_Intance
    End Function

    Public Property Name() As String
        Get
            Return Me.m_Name
        End Get
        Set(ByVal value As String)
            Me.m_Name = value
        End Set
    End Property
End Class

更简单的实现(缺点:不支持带参构造函数)

'Singleton模式:一个类只会创建一个实例。
Module Module1

    Sub Main()
        Dim In1 As Singleton = Singleton.Intance
        In1.Name = "李小龙"
        Dim In2 As Singleton = Singleton.Intance
        System.Console.WriteLine(Object.ReferenceEquals(In1, In2) = True)
        System.Console.WriteLine(In1.Name)
        System.Console.WriteLine(In2.Name)
        System.Console.ReadLine()

    End Sub

End Module

Public Class Singleton
    Private m_Name As String
    Public Shared ReadOnly Intance As New Singleton
    Private Sub New()

    End Sub

   

    Public Property Name() As String
        Get
            Return Me.m_Name
        End Get
        Set(ByVal value As String)
            Me.m_Name = value
        End Set
    End Property
End Class

Singleton模式扩展思想:从一个实例扩展到n个实例,例如对象池的实现.
Singleton模式核心思想:如果控制用户使用New对一个类的实例构造器的
任意调用

[[it] 本帖最后由 ioriliao 于 2008-2-18 11:32 编辑 [/it]]

.Net 框架中singleton模式的应用
一个简单的例子

Dim cl1 As New MyClasses
        Dim cl2 As New MyClasses

        Dim ct1 As Type
        Dim ct2 As Type
        '错误写法 Dim ct3 As New .... 你将会看到 加上New关键字后,智能感知将不会感知到Type
        '可知Type类是singleton模式的.

        ct1 = cl1.GetType
        ct2 = cl1.GetType

Public Class MyClasses

End Class