Exposing generic inherited methods to COM

Question

I'm developing a COM Visible DLL and try to re-use parts of my code by inheriting base classes. This works fine until I use a base class with a generic type. Although the generic type itself is never exposed it still doesn't work. I'm trying to think this is some sort of bug.

Here is an oversimplified version for testing:

Imports System.Runtime.InteropServices

Public MustInherit Class TestGeneric(Of T)
    Private _Value As T

    Public Sub DoSomething(Value As T)
        _Value = Value
    End Sub
End Class

<ClassInterface(ClassInterfaceType.AutoDual)>
Public Class TestString
    Inherits TestGeneric(Of String)
End Class

<ClassInterface(ClassInterfaceType.AutoDual)>
Public Class TestInteger
    Inherits TestGeneric(Of Integer)
End Class

After compiling I register the DLL and use it in VB6. In VB6 I can see both classes TestString and TestInteger but they do not have any methods. I would expect them to show TestString.DoSomething(Value as string) and TestInteger.DoSomething(Value as integer). These methods themselves do not contain generic types, they are just based on a generic type in the backend. Why would this these methods be exposed?

Answer 1

It may not be the most elegant solution but the following worked in my simple test -

Imports System.Runtime.InteropServices


<ComVisible(False)>
Public MustInherit Class TestGeneric(Of T)
    Private _Value As T

    Public Sub DoSomething(Value As T)
        _Value = Value
    End Sub

    Public Function GetValue() As T
        Return _Value
    End Function
End Class

<InterfaceType(ComInterfaceType.InterfaceIsDual)>
Public Interface ITestString
    Sub DoSomething(s As String)
    Function GetValue() As String
End Interface

<InterfaceType(ComInterfaceType.InterfaceIsDual)>
Public Interface ITestInteger
    Sub DoSomething(i As Integer)
    Function GetValue() As Integer
End Interface

<ClassInterface(ClassInterfaceType.None)>
Public Class TestString
    Inherits TestGeneric(Of String)
    Implements ITestString

    Private Sub ITestString_DoSomething(s As String) Implements ITestString.DoSomething
        MyBase.DoSomething(s)
    End Sub
    Private Function ITestString_GetValue() As String Implements ITestString.GetValue
        Return MyBase.GetValue()
    End Function
End Class

<ClassInterface(ClassInterfaceType.None)>
Public Class TestInteger
    Inherits TestGeneric(Of Integer)
    Implements ITestInteger

    Private Sub ITestInteger_DoSomething(i As Integer) Implements ITestInteger.DoSomething
        MyBase.DoSomething(i)
    End Sub
    Private Function ITestInteger_GetValue() As Integer Implements ITestInteger.GetValue
        Return MyBase.GetValue()
    End Function
End Class