I have an ASP.NET (MVC) application in which I would like to load WebForms .aspx files that are embedded as resources in 3rd party assemblies. The reason I want to do this is to make a sort of "plug-in" system where a .dll file can be dropped in a folder and then picked up at runtime to provide additional functionality to the base application.

I've gotten the plugin system to work (I'm using MEF) with plugins written in ASP.NET MVC (Views and Controllers), but for plain old ASP.NET (Pages), I've got myself into a bit of a problem.

For the execution of the embedded .aspx file (which, in the usual WebForm way Inherits="My.BasePage") I've created a custom VirtualPathProvider, ResourceFile ControllerFactory and PageController. Within the PageController I've overridden the Execute(RequestContext) method and within it I'm trying to compile the .aspx with BuildManager.CreateInstanceFromVirtualPath(virtualPath, type).

When doing this, I get the error message "Could not load type 'My.BasePage'", even though I'm giving the BuildManager the System.Type of My.BasePage in the call to CreateInstanceFromVirtualPath. I seem to be stuck at this point. I've tried to Server.Transfer() to the custom VirtualPathProvider handled URL to the same .aspx file, but that fails with the same error message.

How can I help BuildManager find out where My.BasePage is defined and how come the Type requiredBaseType parameter of CreateInstanceFromVirtualPath seems to be ignored?

I've tried to call BuildManager.AddReferencedAssembly(), but that only fails with "This method can only be called during the application's pre-start initialization stage". MSDN says: "The method must be called during the Application_PreStartInit stage of the application", but I have no such event in my HttpApplication object and find absolutely zero information about it on the internet.

Either way, I don't want to be calling BuildManager.AddReferencedAssembly() in or before the Application_Start event, since that makes me have to recycle the whole application to be able to add new plugins to the system.

Does anyone have any clues? Any other ideas on how I can "execute" an .aspx file that is embedded as a resource within an assembly through reflection? Can I for instance pre-compile the .aspx file within the same assembly as the base Page class it inherits?