I have a VSTO addin, which works fine. I am trying to give it a plugin-loading mechanism so that others can add plugins to my plugin. I sounds horrific, I know, but it seems to best option for now.
I publish my addin to a folder called 'Published'. This creates the application manifest (Symbols.application) and also a folder called Symbols_x.y.xx.yy with the actual addin assemblies in it. Visual Studio increments this version number each time I publish, so the assemblies are never in the same place twice.
The plugins are in a folder Published\Plugins. I load the plugin assemblies using Assembly.LoadFile(string) and this works OK. The plugins are all in folder which stays in the same place no matter how many times I publish it and I can scan that folder for DLLs and load them.
What doesn't work is when those plugin DLLs have dependencies. In particular, one depends on a COM object. Visual Studio builds an automatic Interop DLL which it puts in the Published\Plugins folder, alongside the corresponding plugin DLL. An exception is thrown as soon as any attempt is made to access the COM object, saying that the interop assembly could not be found.
Putting the interop DLL into the folder Published\Symbols_x.y.xx.yy folder works, but that requires manually putting it there each time. I've tried adding the plugins to the AppDomain's PrivateBinPath, but the documentation says that anything outside the ApplicationBase will be ignored and it seems this is indeed the case - it doesn't work. ApplicationBase is set to Published\Symbols_x.y.xx.yy.
It seems to me I have four options:
- Figure out how to change the ApplicationBase, moving it up one level, and then add the Published\Plugins folder to the AppDomain's PrivateBinPath.
- Make some change to the application manifest to indicate that assemblies can be loaded automatically from Published\Plugins.
- Find some other way of explicitly loading an assembly into the AppDomain, not just into memory using Assembly.LoadFile.
- Anything else anyone wants to suggest!
But I can't find any way to get any of these options to work. Help!