How do I return a reference to an interface from a WCF contract?

Question

I have a WCF service. I can return a concrete class without a problem, but returning a reference to an interface causes the following issue.

CommunicationException occurred "The socket connection was aborted. This could be caused by an error processing your message or a receive timeout being exceeded by the remote host, or an underlying network resource issue. Local socket timeout was '00:00:59.2030000'."

This occurs when I try to get an instance of a class from a WCF service:

//create the connection
ChannelFactory<IService> _ChannelFactory = new ChannelFactory<IService>(_EndpointName);
IService _ServiceProxy = _ChannelFactory.CreateChannel();

//communication exception thrown here
ITestInterface okcomputer = _ServiceProxy.GetTest();

IService and ITestInterface have all the normal OperationContract attributes and such. The Service has the attribute: [ServiceBehavior(InstanceContextMode = InstanceContextMode.Single)]

other than that, the classes and interfaces are nothing special.

I feel like there is some special trick to returning a class interface from a WCF interface, otherwise I wouldn't be having this problem.. What's the trick?

Answer 1

You cannot return an interface, ever. How would it be serialized?

Interfaces are about behavior. Behavior is not serialized, only data.

Answer 2

John is right you want to return an instance of a class that implements the interface. But from the exception it looks like simply attempting to return the interface is not your problem. Have you tried digging down into the inner exceptions if they're any?