[RESOLVED] COM Visible library fails to access the UI thread?

[3raser]

For reference, this is the code for testing a callback.

.NET interface that defines the callback class.

Imports System.Runtime.InteropServices

<ComVisible(True),
    InterfaceType(ComInterfaceType.InterfaceIsIDispatch)>
Public Interface IControlCallback

    Sub TestCallback()

End Interface

.NET class for testing the callback. This uses the same frmTest form as before.

Imports System.Runtime.InteropServices

<ComVisible(True),
    ClassInterface(ClassInterfaceType.AutoDual)>
Public Class TestCallback

    Private WithEvents _Form As New frmTest
    ReadOnly Property Callback As IFromCallback

    Public Sub SetCallback(Callback As IFromCallback)
        _Callback = Callback
    End Sub

    Public Sub ShowNonModal()
        _Form.Show()
    End Sub

    Public Sub ShowModal()
        _Form.ShowDialog()
    End Sub

    Private Sub _Form_Testing() Handles _Form.Testing
        If Callback IsNot Nothing Then
            Callback.TestCallback()
        End If
    End Sub

End Class

In VB6 I created a callback class for handling the code that should run when clicking the .NET form button.

Option Explicit
Implements IFormCallback

Private Sub IFormCallback_TestCallback()
    Debug.Print "Callback hit!"
    MsgBox "Testing msgbox through callback"
    'Now open a modal form through the callback.
    frmTest.Show 1
End Sub

Now in VB6 create the code for running the .NET class with a reference to the VB6 callback class.

Private Sub Command1_Click()
    Dim Callback As New FormCallback
    Dim TestNetCallback As New TestCallback
    TestNetCallback.SetCallback Callback
    TestNetCallback.ShowModal
End Sub

And to my surprise, this now works! I will test this more thoroughly to see what I missed last time.