I have an old MFC app written in Visual Studio 6. This will at some point be rewritten in C# .NET. However, before then I have to write a couple of new Windows services for the existing application. The others were written in ATL. What I would prefer to do is write these new services in C# .NET so that when the rest of the application is rewritten, these don’t need to be.
Is it going to be possible to call the interfaces on the libraries hosted in a .NET windows service from the old application? If so, could you please explain how.
Absolutely. You’re looking for a feature of .NET called COM-Interop.
http://msdn.microsoft.com/en-us/library/kew41ycz%28v=vs.71%29.aspx
http://msdn.microsoft.com/en-us/magazine/cc163494.aspx
The second link has an ATL example.
EDIT:
Based on your feedback in the comments, let me expand on this…
Ah – you’re right about the sample on that page.
The first link is really where you want to start for all the details. If you follow the links, you’ll find this page:
“Exposing .NET Framework Components to COM”
http://msdn.microsoft.com/en-us/library/zsfww439%28v=vs.71%29.aspx
Essentially, it’s just a matter of applying a series of attributes to your classes and properties, and then generating the appropriate registry entries on the client machine (which .NET has a tool to do – see: http://msdn.microsoft.com/en-us/library/bctyca52%28v=vs.71%29.aspx)
I’ve done this several times myself for .NET projects people needed to call from VC++ and/or VB6.
Some other links that might be of interest:
http://www.codeproject.com/KB/COM/nettocom.aspx <– Perfect example of what you’re trying to do.
http://www.codeproject.com/KB/COM/Universal_CCW.aspx