Side-By-Side COM Interop with C# and VBA

Question

I'm not talking about calling a VBA COM from C#... the other way around!

What I would like to do is call a C# library using VBA in MS Access without registering the DLL. I've been playing around with side-by-side interop for a while without success and it has finally occurred to me that a mdb.manifest is probably not an acceptable replacement for an exe.manifest (probably obvious, I know, but I was trying to be optimistic).

My question: Is it possible to get VBA to load a side-by-side COM component?

Or, is there another way to use an unregistered C# library in Access?

(Before you ask, my reasons are: there is absolutely no way I will be granted access to my client's Windows registry -- that's why it was written in Access in the first place. And, I will need to implement the same functionality in a C# application soon and rather not do it twice).

Answer 1

C# libraries are not regular DLLs. They're more similar to COM libraries which need to be registered (just like ActiveX controls) before being used; especially when called from non-.NET code.

(Unless, of course, things have changed...)

Answer 2

The problem is that to use SxS, you need to own the exe to set up the config to load the SxS assembly. You don't "own" Access, and while you could drop the right config in to cause it to load your .NET COM stuff sans registration, it wouldn't be a "good citizen" move.

If you get tricky with shimming, you can set up an unmanaged DLL (or a hacked C# class library with a dllexport, see this, for example) with an export that will load the .NET framework, create an instance of a COMVisible DispInterface managed type and return it (the method should return IDispatch). Then write a VBA declare to your DLL export function (declared as returning Object). If this doesn't make sense, you probably oughtn't try it... :) I've done this before in a similar situation, and it does work, but I don't have a sample to point you at.

Answer 3

You don't have to own the exe to use SxS, SxS is another word for Activation Context. If you can import the relevant win32 calls into vba (and you can), then you can use the activation context api to load your manifest file.

More on the subject and some examples can be found here.