ComVisible C# DLL causing Error 438 in VB6.0

Question

i've written a DLL in C# (.NET v4) which I want to use in a VB6.0 Projekt. I basicly followed the tutorial at http://msdn.microsoft.com/de-de/library/ms227568(v=vs.80).aspx and ended up with this class

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Runtime.InteropServices;

namespace CRUFL_CS_ExchangeRate
{
    [Serializable]
    [ComVisible(true), ClassInterface(ClassInterfaceType.None), Guid("F5DCE88F-AD38-4a9a-9A69-0F8DC0EDB4E3")]
    public class ExchangeUfl : IExchangeUfl
    {
        public double ConvertUSDollarsToCDN(double usd)
        {
            return (usd * 1.45);
        }

        public void bla()
        {
        }

        public string t2()
        {
            return "t2";
        }

        public String test()
        {
            return "test";
        }
    }
}

and this Interface

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Runtime.InteropServices;

namespace CRUFL_CS_ExchangeRate
{
    [ComVisible(true), InterfaceType(ComInterfaceType.InterfaceIsDual), Guid("F6B3D6DB-E4C8-48A9-B9B5-324012E2E93F")]
    interface IExchangeUfl
    {
        [DispId(1)]
        double ConvertUSDollarsToCDN(double usd);

        [DispId(2)]
        String test();

        [DispId(3)]
        string t2();

        [DispId(4)]
        void bla();
    }
}

My AssemblyInfo.cs look like this

using System.Reflection;
using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;

[assembly: AssemblyTitle("CRUFL_CS_ExchangeRate")]
[assembly: AssemblyDescription("")]
[assembly: AssemblyConfiguration("")]
[assembly: AssemblyCompany("Microsoft")]
[assembly: AssemblyProduct("CRUFL_CS_ExchangeRate")]
[assembly: AssemblyCopyright("Copyright © Microsoft 2014")]
[assembly: AssemblyTrademark("")]
[assembly: AssemblyCulture("")]
[assembly: Guid("912fe53d-dfc9-4eec-bbca-7f2ed29d95dc")]
[assembly: AssemblyVersion("1.0.0.0")]
[assembly: AssemblyFileVersion("1.0.0.0")]

I've turned on the strong name signing in the project properties and the COM-Interopt registration is off.

I created the project and registered the DLL via "regasm.ex C:\path\to\the\lib.dll /codebase" and it shows up in the GAC (i'm using RegDllView from www.nirsoft.net)

In the VB project I can create the object, so i assume the registration works properly. But when i call one of the methods i got a Run-time error ‘438’: Object doesn’t support this property or method

My VB Code looks like this:

Dim testi As Object
Dim fab As Object
Set fab = CreateObject("CRUFL_CS_ExchangeRate.ExchangeUfl")
Set testi = fab.t2()

It doesnt matter which method i call, i always get the same error :( Am I missing something? Have I done something wrong? Any ideas?

Thanks :)

Answer 1

1. Skip the GAC, and do use the /codebase option.

2. When you register the .NET assemble using RegAsm, also export the typelib using the /tlb option.

3. As a double-check, look in the registry for the objects you just registered in HKCR.

4. In your VB6 project, don't use the CreateObject syntax. Instead, add a refernce to the typelib you exported earlier.

TIP: Avoid underscores in COM public signatures / class names. VB6 treats the underscore with special meaning in some edge cases. It is best to nip that in the bud.