'尝试采用 委托 方式实现，但是第2次执行EndIdentify时，仍然无法获得第1次执行EndIdentify时设置的uid值。代码如下。
Public Class Form
    Private uid As String '当前用户 
    'property   
    Public Property CurrUid() As String
        Get
            Return uid
        End Get
        Set(ByVal value As String)
            uid = value
        End Set
    End Property
    '声明委托
    Public Delegate Function StringPropertyDg(ByVal s As String) As String
    '试图通过这个方法来获得和设置uid
    Public Function StringPropertyGatter(ByVal s As String)  As String
          If(s<>"") Then
                 uid = s
           End If
           Return uid
    End Function    

    Public Sub New()
        InitializeComponent()
        Identify()
    End Sub

    Private Sub Identify()
        Dim threadIdentify As Identify
        threadIdentify = New Identify(Me)
    End Sub    
    Public Sub EndIdentify()    
        '实例化委托
            Dim d As New StringPropertyDg(AddressOf StringPropertyGatter)
            MsgBox(d.Invoke("")) '获取uid的值，每次执行EndIdentify都是空的，何解？
            id.Invoke("123456")'设置uid的值
    End Sub

End Class
Public Class Identify
    Private mainForm As Form
    Public Sub New(ByVal form As Form)
        mainForm = form
        Dim td As New Thread(AddressOf IdentifyStart)
        td.Start()
    End Sub
    Private Sub IdentifyStart()
        mainForm.EndIdentify()
    End Sub
End Class