TextBox不会在主窗口WPF上更新

Question

我有一个程序拦截来自SMS调制解调器的短信，然后它意味着从我的代码的另一个类更新主窗口上的TextBox：

主窗口：

Class MainWindow
Public WithEvents SMScon As SMSComms
Private Delegate Sub GetDisplay(ByVal SMS As SMSMessage)

Public Sub GetFromSMSComms(SMS As SMSMessage) Handles SMScon.SMSListChanged
    If tb_recievedmessages.Dispatcher.CheckAccess() Then
        DisplaySMS(SMS)
    Else
        tb_recievedmessages.Dispatcher.BeginInvoke(DispatcherPriority.Normal, New GetDisplay(AddressOf DisplaySMS), SMS)
    End If
End Sub

Private Sub DisplaySMS(ByVal SMS As SMSMessage)
    Debug.WriteLine("Writing To TextBox")
    tb_recievedmessages.Text() = SMS.MessageText
End Sub
End Class

在另一个班级中捕获的短信：

SMSComms.vb：

Public Class SMSComms

   Public Event SMSListChanged(ByVal SMS As SMSMessage)

Private Delegate Sub GetDisplaySMSCallback(ByVal SMS As List(Of String))

Public Sub DataReceivedHandler(sender As Object, e As SerialDataReceivedEventArgs)

    Dim rxString As String
    Dim index As Integer
    Dim newMsg As New SMSMessage

    RemoveHandler SMSPort.DataReceived, AddressOf DataReceivedHandler

    Thread.Sleep(100)
    rxString = SMSPort.ReadExisting()
    rxString = TrimCRLF(rxString)

    index = NewSMSIndex(rxString)
    If index > -1 Then

        newMsg = ReadSMS(index)
        If newMsg.Index > -1 Then


            AddHandler SMSListChanged, AddressOf Main.GetFromSMSComms

            RaiseEvent SMSListChanged(newMsg)


        End If

    End If
    RemoveHandler SMSListChanged, AddressOf Main.GetFromSMSComms
    AddHandler SMSPort.DataReceived, AddressOf DataReceivedHandler

End Sub
End Class

现在SMS对象从SMSComms类传递到主窗口，我使用Dispatcher.BeginInvoke（）来调用主线程但是当它到达写入文本框的子对象时，文本框不会更新在主UI上。

谁能告诉我为什么？或者如何更新??