Used Fields

Hello,

I am looking to fill a dropdown with picklist that are currently being displayed on a specific entity, i.e. used vs. unused when customizing a form.   Here is my call, then on the response, I filter by Attribute type of "picklist" but I cannot find what is saying whether it is used on the view or not:

try

           {

               OrganizationRequest request = new OrganizationRequest() { RequestName = "RetrieveEntity" };

               request["EntityFilters"] = EntityFilters.Attributes;

               request["RetrieveAsIfPublished"] = false;

               request["LogicalName"] = entityName;

               request["MetadataId"] = Guid.Empty;

               _service.BeginExecute(request, new AsyncCallback(FillFieldComboComplete), _service);

           }

           catch (Exception ex)

           {

               return;

           }