Debugging adding known types through config

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 开发者_开发技巧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?

If you are looking for a way to debug your windows service you could try adding the line System.Diagnostics.Debugger.Break(); at service startup. I don't know whether this is sufficiently early to find out why the serialization infrastructure isn't picking up your dataContractSerializer.

I cannot see any errors in the <system.runtime.serialization> element that you have posted. Have you investigated the rest of the exe.config file for semantic errors?

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.