Catching ActiveX callback in C#

[d00_ape]

I’m using a third party ActiveX control in my .NET Application. I manage to handle the callback in unmanaged C++ like this:

class MyCallback : public ICallback
{
   …
   void OnComplete() {…}
}
…
MyCallback *callback = new MyCallback();
someobject->SomeFunction(“just a string”, callback);

The function OnComplete is apart of the ICallback interface.
In C++ the method OnComplete will be called some seconds after SomeFunction has been called.

How do I translate that into C#?

I’ve come this far:

public class MyCallbackSC  : ICallback
{
   …
   void OnComplete() {…}
}
…
MyCallback callback = new MyCallback();
someobject.SomeFunction(“just a string”, (object)callback);

My C# program compiles fine but when I got an exception on the codeline above that says: InvalidCastException.

Anyone got any ide how to handle callbacks in C#...?