只允许创建一个实例的VB.NET窗口

利用Shared属性值是唯一的，实现只允许创建一个实例的VB.NET窗口：

FORM1中的代码：

    '确保只调用一次这个Form1
    Private Shared frmThisform As Form1
    Public Shared Property OnlyOneInstance() As Form1
        Get
            If frmThisform Is Nothing OrElse frmThisform.IsDisposed Then
                frmThisform = New Form1
            End If
            OnlyOneInstance = Form1
        End Get
        Set(ByVal Value As Form1)
            frmThisform = Value
        End Set
    End Property

显示Form1调用时的代码：

        With Form1.OnlyOneInstance
            .MdiParent = Me
            .Show()
            .WindowState = FormWindowState.Maximized
        End With

或者是：

Module Module1

    Sub Main()

        Application.Run(Form1.OnlyOneInstance)  

    End Sub

End Module