Debugging adding known types through config

Question

I've been going round this for a while now and I can't figure out why I can use the config to add references to known types, or how to go about debugging it. Any pointers might save my sanity.

I have a WCF service hosted in a windows service, and I have a config file for the service. In the config I have this:

<configuration>
...
  <system.runtime.serialization>
    <dataContractSerializer>
      <declaredTypes>
        <add type="My.Full.Interface.Name, My.Assembly.Name.With.No.dll">
          <knownType type="My.Full.Implementation.Class.Name, My.Assembly.Name.With.No.dll"/>              
        </add>
      </declaredTypes>
    </dataContractSerializer>
  </system.runtime.serialization>
...
</configuration>

I have tried adding the Version=1.0.0.0,Culture=neutral,PublicKeyToken=null to both declarations, but I can't seem to make the data contract serializer pick them up.

I have verified that this class can be returned (by adding a [ServiceKnownType(typeof(My.Implementation.Class))]) and that works, but I have another implementation that I want to use that is in anothet assembly that would create a circular reference if I added it, so can't use that.

How can I debug why the datacontract serializer is not finding my type? Or what is wrong with my declaration?

Answer 1

So it seems that my issue was that my base type is an interafce, and as KnownType attributes can only be applied to classes this is why it was not working.

I was able to work around it by using the suggestion in this answer

 [ServiceKnownType ("GetKnownTypes", typeof (KnownTypesProvider))] 

on the service inteface and then providing a class and method to provide the types:

internal static class KnownTypesProvider
    {
    public static IEnumerable<Type> GetKnownTypes (ICustomAttributeProvider provider)
        {            
        return new[] {Type.GetType ("Assembly qualified type name")};
        }
    } 

which also allowed resolution of types which are in different assemblies. Whilst this works it's not great so I'll probably end up going to a solution which uses configuration like in this answer, or by adding soem attribute to my classes and using that to identify known types.