I have been re-reading the ”Upgrading Visual Basic 6.0 Applications to Visual Basic .NET and Visual Basic 2005” guide lately which discusses phased migrations where individual application components are upgraded independently (which I prefer to call “Extending with .NET”). This approach relies on COM Interop to get the old VB6 components talking to the new .NET components – which is great for Business Logic. What the guide doesn’t address are the possibilities opened up by the Interop Forms Toolkit which was released after the guide was written. The Toolkit (amongst other things) allows an application to mix Visual Basic .NET User Interface (UI) with VB6 UI. E.g. An application with 100 VB6 forms could have the 101st form written in Visual Basic .NET – and the users would never know.
It is a real shame we didn’t have the Interpop Forms Toolkit in place when we released the first version of Visual Basic .NET back in 2002. It would have significantly simplified the roadmap and effort involved for companies with VB6 applications.
NB: You can also use C# with the Interop Forms Toolkit to extend VB6 applications.