Question

How does a WCF channel (created via ChannelFactory) implement ICommunicationObject, but doesn’t expose the Close() method, for example, unless you cast the proxy to ICommunicationObject? Does that make sense?

I got to thinking about that on the way home today and couldn’t figure it out in my head. Maybe I’m asking the wrong question? Maybe I’m asking a stupid question? 🙂

Is it some kind of ninja trick?

Answer 1

This is done via Explicit Interface Implementation.

Suppose you have an interface, like so:

public interface IFoo
{
     void Foo();
}

You can implement this normally:

public class Bar : IFoo
{
     public void Foo() {} // Implicit interface implementation
}

Alternatively, you can implement the interface members explicitly, which requires the cast:

public class Baz : IFoo
{
     void IFoo.Foo() {} // This will require casting the object to IFoo to call
}

This can be very useful at times. For example, it is often done to implement IDisposable in classes where the preferred API would be to call .Close(), for example. By implementing IDisposable explicitly, you “hide” the Dispose() method, but still allow the class instance to be used via a using statement.