Referencing .NET Assembly in VB6 won't work

Question

I wrote a .net assembly using c# to perform functions that will be used by both managed and unmanaged code. I have a VB6 project that now needs to use the assembly via COM.

I created my .net assembly, made sure that ComVisible is set to true and that it is registered for COM interop via project properties.

public class MyClass

    [ComVisible(true)]
    public string GetResponse()
    {
        return "Testing Response"
    }

}

I build the assembly and copied the file into a folder. TestInterop.dll

I then run a batch file to register the assembly tool to register the object for COM.

cd C:\Windows\Microsoft.NET\Framework\v4.0.30319\
regasm "c:\Program Files\TestApp\TestInterop.dll" /tlb:TestInterop.tlb

I open a new VB6 application and reference TestInterop.dll

In VB6 I write the following code and it compiles.

Dim obj as TestInterop.MyClass
Set obj = new TestInterop.MyClass

Dim strTest as string

strTest = obj.GetRespose()

When I run the program it errors on the obj.GetResponse() line.

Run-time error' -2147024894 (80070002'):
Automation error
The system cannot find the file specified

Also, the intellesense does not work on obj. I had to type the GetResponse method. Is this normal?

Does anyone have any clue what could be wrong or what steps I missed. Thanks!

Answer 1

You'll want to put your .NET assembly in the GAC or else run RegAsm with the /codebase command line switch (it will complain, but this will at least work). No intellisense is normal, unfortunately.

Answer 2

Last time I saw that I forgot to hard-code the GUIDs. So every time I recompiled VB would be unable to find my code. This is a template from VB.NET. (Don't use these GUIDs, make your own.)

<ComClass(ComClass1.ClassId, ComClass1.InterfaceId, ComClass1.EventsId)> _
Public Class ComClass1

#Region "COM GUIDs"
    ' These  GUIDs provide the COM identity for this class 
    ' and its COM interfaces. If you change them, existing 
    ' clients will no longer be able to access the class.
    Public Const ClassId As String = "eaf83044-f0a7-417b-b333-e45aec398ca5"
    Public Const InterfaceId As String = "84e0fb8f-266d-40e6-9e8c-3d4eb37d3bf0"
    Public Const EventsId As String = "22ea2214-032f-4eb6-b2d4-c5dd213bab87"
#End Region

    ' A creatable COM class must have a Public Sub New() 
    ' with no parameters, otherwise, the class will not be 
    ' registered in the COM registry and cannot be created 
    ' via CreateObject.
    Public Sub New()
        MyBase.New()
    End Sub

End Class

Answer 3

I think, the tlb file is generated under the framework directory as against this directory (c:\Program Files\TestApp).

Could that be the problem here?

Answer 4

I have noticed that you don't need to run the RegAsm manually, actually just set AssemblyInfo property ComVisible to true:

[assembly: ComVisible(true)]

You can also do this by going to Project properties -> Application -> Assembly Information -> Make Assembly COM Visible, and set the check box.

It is not required to register the assembly you are creating into the GAC in order to use it from VB6.

Answer 5

I was having the -2147024894 error, or other errors no matter what I tried, until I ran the vb6 consumer code directly from exe. Something about the VB6 debugger that was preventing from allowing me to use the dll at runtime. I couldn't even instantiate the object. I could reference the tlb at design time, and had perfect intellisense support too. As soon as I launched the application outside of Visual Studio everything worked perfectly. Hope this helps someone.