OK, so with the way you have called this method it is expecting the
interface to live within your application (assembly). If you want this to
work you will have to add the assembly name on to the string. Suppose the
assembly housing the Runtime Callable Wrapper (I assume you have already
created an RCW) is called MyCOMStuff.dll and has been signed with a public
key token, then you need to pass in something like

wca.AddType, MyCOMStuff, Version=0.0.0.0, Culture=neutral,
PublicKeyToken=<token used for signing>

This will get you the type object for the interface. The question is, is
this really what you want? Aren't you trying to find out if a specific
object implements an interface or have I misunderstood?

Regards

Richard Blewett
DevelopMentor
http://www.dotnetconsult.co.uk/weblog2

I don't know much about what your trying to do....but GetType() accepts a
string parameter, so maybe it should be:

Type at = Type.GetType("wca.AddType");

What exactly do you mean with "string name of a COM interface" here?

Type at = Type.GetType(wca.AddType); // Add type is a string name of a COM
interface.

what does wca.AddType contain?

Interfaces are identified using UUID's, so you need to specify the UUID of
the interface (the IID) you are looking for in a call to QI.
Herewith a small sample calling a method on a native COM object using late
binding.

           string progId = "SimpleCom.Bird";
           Type t = Type.GetTypeFromProgID(progId);
           if (t == null)
           {
               throw new Exception("Invalid ProgID.");
           }
           Console.WriteLine("GUID for ProgID RemServer.Server is {0}.",
t.GUID);
           object o = Activator.CreateInstance(t);    // create an instance
of this server
           IntPtr pUnkn = Marshal.GetIUnknownForObject(o);    // Get the
IUnknow pointer
           Guid IID = new Guid("0938B479-ED9A-4997-B780-85AF420E01FF"); //
This is the Interface I need
           IntPtr ppv;
           int hResult = Marshal.QueryInterface(pUnkn, ref IID, out ppv);
// Does above Interface exists?
           if(hResult <  0)
           { throw ...            }
           else
           {
               // success, use interface
               object bird = Marshal.GetObjectForIUnknown(ppv);
               //late bound call
               bird .GetType().InvokeMember("Fly",
BindingFlags.InvokeMethod, null, bird , new Object[] {"To Somewhere"});

               ...

Willy.