Question

I have a ASP.net application that is referencing a external assembly that I need to dynamically load and discover any types implementing a known interface. The problem I am having is that the type I reflect does not match the same interface that is running and so I cannot cast it.

Example:

This code is run in ASP.net app.

var assembly = Assembly.LoadFile(Path.Combine(HttpRuntime.BinDirectory, "ExternalAssembly.dll"));

var type = assembly.GetExportedTypes().First<Type>(x => x.Name == "AClass"); // AClass implements IAInterface

var reflectedInterface = type.GetInterface(typeof(IAmAInterface).ToString());

if (reflectedInterface != typeof(IAmAInterface))
    throw new Exception("This makes me sad"); // This code gets run

The only difference I can see between the reflected interface I loaded from the bin and the interface returned from typeof is that the typeof assembly has a location in the temp ASP.net path (C:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\Temporary ASP.NET Files\root\08c43c8b\3adac8cf\assembly\dl3\eb7a4127\0235ea60_a3c8c901\ReflectionTest.DLL)

Thanks Paul Alexander I have changed the code to use the Assembly.Load method not Assembly.LoadFile which solves the problem.

wwilden: I also tried extracting the interface into it’s own assembly and this does also solve the problem.

Answer 1

When you use LoadFile the assembly is not loaded into the same context as your other assemblies at runtime so to the CLR interface runtime types are different. You can read more in Suzanne Cook’s Debugging Assembly Load Failures.

If the assembly that you’re loading is already in the Bin directory – you can load it by name. You don’t need to know the exact path as the Bin folder is already in the assembly probing path.