Consuming .NET dll in VB6 application

Question

I wrote a dll in c#.net that calls another third party .NET dll within the application. This works fine when I tested it with a console application written in c#.NET as well using the code below:

 Assembly u = Assembly.LoadFrom(dllLocation);
 Type t = u.GetType("MyLIB.CLass");
 MethodInfo m = t.GetMethod("Method");
 object[] myparam = new object[1];
 myparam[0] = fileLocation;
 result = (string)m.Invoke(null, myparam);

Please note that some files are loaded within the location where the dll was initially loaded as well using:

  string path = Assembly.GetExecutingAssembly().Location;
  path = Path.GetDirectoryName(path);

But the issue is that when I tried to call it using VB6, I get an error that it cannot load the third party dll. Please help as I seem not to know what's going on.

What is the exact error? And have you checked that it is looking in the correct location? — MarkJ
– MarkJ, Commented Sep 18, 2012 at 7:01
The exact error is "it cannot find the third party dll or one of it's dependencies are missing". Please how can I check if it is looking in the current location in VB6? — Jay
– Jay, Commented Sep 18, 2012 at 7:18
looks like you need to check with the vendor who supplied you the third party dll and ask for COM interop support. — Turbot
– Turbot, Commented Sep 18, 2012 at 13:15

Turbot · Accepted Answer · 2012-09-17 19:00:59Z

6

I would thought to give you more detail, in order .NET Assembly expose to COM

you need to generate the tbl - type library

using RegAsm /tlb: MyLIB.tlb MyLIB.dll

There are Guidelines to expose .NET Types to COM and make sure you cope with that. such as declare ComVisibleAttribute , require a public default constructor to be visible to COM , such are in

you can refer that in How to call a Visual Basic .NET or Visual Basic 2005 assembly from Visual Basic 6.0

edited Sep 17, 2012 at 19:00

answered Sep 17, 2012 at 18:53

Turbot

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3 Comments

Jay Over a year ago

I have specified the necessary ComVisibleAttribute to true, generated the type library and also registered the assembly but recall that my .NET dll references a third party dll. That's where the error pops from, but there's no way I could specify the ComVisibleAttribute for the third party dll. Is there any other way around it?

Mark Hurd Over a year ago

You have marked this as the answer, but your comment suggests you wanted the VB6 code to access the third party DLL directly. Just confirming this is not possible, but you can always add code with the ComVisibleAttribute to the DLL you do have control over that passes the calls straight on to the third party DLL.

Turbot Over a year ago

in this case , you couldn't access the .NET Dll reference directly but you can create interfaces and explicit implement them in .NET classes, and generate the COM interop for your VB6 reference. the link I posted provides the guidelines.

Nate · Accepted Answer · 2012-09-17 18:45:23Z

3

You need to specify the ComVisibleAttribute on the assembly in order to call it from VB6.

answered Sep 17, 2012 at 18:45

Nate

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1 Comment

Jay Over a year ago

I have specified the necessary ComVisibleAttribute to true but recall that my .NET dll references a third party dll. That's where the error pops from, but there's no way I could specify the ComVisibleAttribute for the third party dll. Is there any other way around it?

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