ASP.Net MVC: How to dynamically load assemblies (controllers) without an AppPool restart/recycle

Question

I'm trying to write a module/plugin system for a website I'm working on. The overall goals are:

1. That the main website does not have to be recompiled every time a new plugin is added.
2. To be able to dump DLL's and CSHTML files into a set of folders that would basically add a set of routes, controller(s), and any other assemblies that the module depends on (Entity Framework, etc).
3. To avoid marking plugin files as "embedded resources" -- especially views.
4. To be able to add and remove these modules/plugins WITHOUT having to restart/recycle the IIS app pool or unload the app domain.

I got #1-3 working by following the example of Umbraco. Basically, I marked a method with the PreApplicationStartMethod attribute, and in it I shadow copy DLLs around, and use a custom ViewEngine to locate the module's CSHTML files. When my website first starts up, my module's controllers and views are working, and assemblies are loaded: Hooray!

However, when it came time to try part #4, I am getting this error when calling BuildManager.AddReferencedAssembly():

This method can only be called during the application's pre-start initialization phase. Use PreApplicationStartMethodAttribute to declare a method that will be invoked in that phase

It's been a very frustrating process so far, and my gut tells me that this error signifies a dead end. Is this the case, or is there a clever workaround?

Answer 1

"To be able to add and remove these modules/plugins WITHOUT having to restart/recycle the IIS app pool or unload the app domain."

It turns out that this you cannot unload an assembly from an app domain.

How to unload an assembly from the primary AppDomain?

Answer 2

Editing the web.config file when you add the new modules should cause the site to recompile.

You could automate this in a script, forcing your new .dll's to be copied to the live ASP.NET temp files directory.

Answer 3

Check out portable areas. Essentially a regular MVC area (including views, controllers, etc.) gets compiled into a single dll. These dll's (one for each area) can be dropped into a hosting MVC website and can be called like any other MVC area.

Some references to get started:

Portable Areas three years later – Part 5

MvcContrib Portable Areas