I have an interface and a class defined in separate assemblies, like this:

namespace DataInterfaces
{
    public interface IPerson
    {
        string Name { get; set; }
    }
}

namespace DataObjects
{
    [DataContract]
    [KnownType( typeof( IPerson ) ) ]
    public class Person : IPerson
    {
        [DataMember]
        public string Name { get; set; }
    }
}

This is my Service Interface:

public interface ICalculator
{
    [OperationContract]
    IPerson GetPerson ( );
}

When I update my Service Reference for my Client, I get this in the Reference.cs:

public object GetPerson() {
    return base.Channel.GetPerson();

I was hoping that KnownType would give me IPerson instead of "object" here.

I have also tried [KnownType( typeof( Person ) ) ] with the same result. I have control of both client and server, so I have my DataObjects (where Person is defined) and DataInterfaces (where IPerson is defined) assemblies in both places. Is there something obvious I am missing? I thought KnownType was the answer to being able to use interfaces with WCF.

----- FURTHER INFORMATION ----- I removed the KnownType from the Person class and added

[ServiceKnownType( typeof( Person ) ) ]

to my service interface, as suggested by Richard. The client-side proxy still looks the same,

public object GetPerson() { return base.Channel.GetPerson();

, but now it doesn't blow up. The client just has an "object", though, so it has to cast it to IPerson before it is useful.

        var person = client.GetPerson ( );
        Console.WriteLine ( ( ( IPerson ) person ).Name );