Merging two .IDL files or two .tlb files into one file

Question

I have 2 .net dll's which I expose to COM using REGASM. In order to simplify referencing within a COM client I would like to make these into one file.

I have tried converting both files to IDL and then copying the contents of the Library section of one into the other and then compiling back to .tlb with MIDL. This works fine for the TypeDefs within the second IDL however it seems to fail when it comes to the interfaces I copied in. OLE/COM viewer can see the interface definitions but when I try and use the TLB via COM it cant find the interfaces that I copied in.

I wanted to make sure before I spend too much time on this, that it is actually possible to meagre IDL's in this way.

Answer 1

Ok so it turns out that the issues I was experiencing were not related to merging the idl's.

If you wish to merge to idl's you can do so by simply copying the content of a library section in one idl into another. Then run midl on the merged file to turn it into a tlb.

Answer 2

Could you use ILMerge to first combine the .NET assemblies and then use REGASM on the resulting assembly?

ILMerge is a utility for merging multiple .NET assemblies into a single .NET assembly. It works on executables and DLLs alike and comes with several options for controlling the processing and format of the output.

Answer 3

I don't see an obvious way this would fail. You said you merged the library sections but you didn't say you copy-pasted the interface declarations from the other .idl. That would be an obvious, but unlikely, explanation.

One failure mode is when the client app uses the type library to marshal interface pointers across apartment boundaries or out-of-process. That however requires registry keys in HKCR\Interfaces. .NET doesn't create them, you'd have to do that yourself. You'd know if you did, not much of an explanation either.