This:
Type app = a.GetType("App");
is looking for a type with a namespace-qualified name of App
.
Your type is called App
in a namespace of App
, so Assembly.GetType
is returning null
, and then you're dereferencing it. Instead, you should use:
Type app = a.GetType("App.App");
However, you shouldn't give a class the same name as its namespace in the first place. Fix that, so that you end up with something more like:
Type app = a.GetType("App.PlugIn");
You should still check whether GetType
(or GetMethod
) returns null, in order to fail rather more gracefully and with more information.
Additionally, you should start following .NET naming conventions - give methods names in PascalCase. Oh, and you might want to consider a common interface for your add-ins rather than relying on reflection to call methods.