Exposing .NET COM Interfaces to VB6

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I was looking at an article by Muhammad Musa Ali entitled "Exposing COM interfaces of a .NET class library for Late Binding"

I did Solution 1, which was to create a COM object using the COM class template of Visual Studio.NET.

So I have a .NET DLL that is exposed as a COM interface, and in the same solution I have a .NET container project that accesses it. The purpose of the COM object is to get a connection string out of app.config. I also added a property called "Color" that returns a simple string for testing purposes.

In the .NET container both properties work as expected returning the connection string and the color.

When I reference the DLL in VB6 the color property works fine but the connection string property fails with this error:

Overload resolution failed because no Public (Item) is most specific for these arguments:
    'Public ReadOnly Property Item(index As Integer) As String':
        Not most specific.
    'Public Property Item(name As String) As String':
        Not most specific.

I googled this error and I've spent over a day trying to get this working. If you have any idea what might be causing this I would greatly appreciate any advice.

Thanks,

Jerry

Posted 2-Nov-10 2:35am

Jerry44

Updated 2-Nov-10 2:50am

Johnny J.

v3

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Jerry44 · Answer 1 · 2010-11-02T04:54:00

Solution 2

I also put some logging in the DLL. The connection string name is getting passed to the object.

It is apparently not finding the app.config file. I have the app.config file in the same directory as the test file for the VB6 project.

Posted 2-Nov-10 4:54am

Jerry44

Comments

Nish Nishant 2-Nov-10 11:09am

Ok, so your error now has nothing to do with the original error you mentioned in your initial question. This is now more to do with the config file not being found in the search path. Perhaps it needs to be in the same folder as the .NET assembly?

Jerry44 2-Nov-10 11:19am

Yes, and I have no idea why it stopped giving that error.

I tried putting it in the folder with the .NET assembly at first and it didn't work. In researching it, it seems that it should go in the folder with the test project.

I found that if you change the name of the app.config to VB6Project.exe.config it works but only if it is compiled into an exe. For some strange reason it doesn't work when you step through the code in the VB6 project.

But at least it is working and I can live with that.

Thanks for taking a look at this.

Jerry

Jerry44 2-Nov-10 18:36pm

Well, I've decided that this not working in debug mode will just not suffice, so I decided to use an INI file and it works just fine.

I regret that I spent so much time on this.

Nish Nishant · Answer 2 · 2010-11-02T03:09:00

Solution 1

Are you sure you are passing a VB6 string to the property index argument? It needs to be a string, which will resolve to a BSTR (which is what the .NET String is exposed as in COM).

Posted 2-Nov-10 3:09am

Nish Nishant

Comments

Jerry44 2-Nov-10 9:31am

Yes. Here is the code:

Private Sub Form_Load()

Dim x As New JKConnect.MyConnect

Dim sColor As String
sColor = x.Color

Dim sConn As String
'sConn = x.ReadConnect("ConnectionString22")

Dim sName As String
sName = "ConnectionString22"
sConn = x.ReadConnect(sName)

End Sub

sColor returns "Blue"

sConn returns ""

Nish Nishant 2-Nov-10 9:36am

And what line throws the error you mentioned?