Extend a C++/MFC application with plugins in C++/MFC and C#

Question

I wonder how to best develop a plugin framework where you can develop plugins with both C++/MFC and C#.

The Host Program is an existing program developed in native C++/MFC. To extend the functionality of this program, we have so far developed separate programs in C++/MFC and C# that run as separate applications or windows services. These programs are now communicating with the host application via files. This is obviously a rather clumsy method, and we therefore wish to bring them under a common plug-in framework.

Each program also has a separate management of settings. We therefore want each plugin to expand the settings window in the host application so that all settings can be managed in one place. How can we do that in a flexible and easy way?

Answer 1

(...) we therefore wish to bring them under a common plug-in framework. (...)

You can do that by creating a set of COM interfaces in a type library that you can wrap in a C++/MFC dll project. Then from either C++ or C# you can import this type library and create new COM classes that implement the predefined interfaces. Two disadvantages of these approach are: 1- That your main application will need to know the class IDs somehow to create instances of the COM classes. 2- Your plugins will need to be registered on the system or you will need to provide manifest files .

(...) We therefore want each plugin to expand the settings window in the host application so that all settings can be managed in one place. (...)

This one is a bit more tricky, but you could try having a tab control with one tab for each plug-in, then pass the window handle of the corresponding tab to each plug-in during initialization, and then use that to place an ActiveX control on it. Creating ActiveX controls in MFC is well documented, and there is a sample project here for doing the same in C#: CSActiveX Sample