CODEWITHSUNDEEP
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RyanMac
RyanMac

Reputation: 767

How can you pass a custom collection class from VB.NET to VB6?

I have recently attempted to port a legacy VB6 application to .NET. It's not a complete port however as I'm focusing solely on the application layer. I'll still be consuming a handful of VB6 COM components.

So far so good, but I recently hit a wall.

I need to pass a custom collection from .NET to VB6. Is this possible?

The COM method I'm calling on the .NET side is expecting a generic object however the application blows up immediately with: InvalidCastException - Specified Cast Not Valid.

I've stumbled upon a few articles that hint on how to pass VB6 collections to .NET but not the other way around. I've tried inheriting from / utilizing a few different collection types in .NET but all to no avail so far. Any help is appreciated.

Upvotes: 1

Views: 787

Answers (1)

Markus
Markus

Reputation: 761

In the COM interface declaration implemented by your .NET collection class, set the DispId for the method that returns your enumerator to -4. Call that method "GetEnumerator".

On the other hand, if you're actually wanting to mock a VBA.Collection object, and not just support For Each in VB6, you can set a reference to the VBA type library in your VB.NET class library (assuming you're creating a class library) and implement _Collection in your VB.NET class.

<Guid("A4C4671C-499F-101B-BB78-00AA00383CBB")>
<ComDefaultInterface(GetType(_Collection))>
<ComVisible(False)>
Public Class VBACollection
   Implements _Collection
   .
   .
   .
End Class

Then just implement the _Collection interface. If VB.NET doesn't like the underscore in the interface name, you may need to escape it.

Upvotes: 1

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