Calling .Net Classes from Visual Basic 6

Question

We have a .Net DLL. We need to call this DLL from a VB Application. What are the procedures we need to follow?

Answer 1

Have a look at

• C# Com
• COM Interop Exposed
• C# Classes as COM Objects
• Real Stories of .NET Interop: C#, VB.NET and VB6

Answer 2

The last time I did this, it got so thorny (some irrelevant issues involving COM+, deployment, etc tripping us up) that I actually ditched the COM boundary, and re-wrote the interface as a POX web-service talking to a handler (ashx) in the .NET. I would give serious consideration to this approach... (unless you need to share windows handles, or similar)

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If you really want a COM API, you need to generate a COM-callable wrapper; this is largely a case of:

• ensuring the necessary types / methods are public
• marking the assembly / types as [ComVisible(true)]
• using tlbexe to export the type library if you need
• using regasm to register the type in COM (either in the GAC or from a fixed location on a drive)

After that your VB6 should just see it as another COM package, but I strongly recommend that you limit this interface to the bare minimum; it isn't change-friendly, and the VB6-style interface forwarding (ie where you can get away with adding a method, without breaking binary compatibility) is not here.