Read PartyList types and items

It is not to say that PartyList data type in Activities are the most complex ones in Dyanmics CRM. They can be called as multi-lookups of multi types. I had to play a bit to understand how I am going to identify item with specific entity type and do something. Though of sharing the code; in this example, I am checking the attendee list of appointment and see if I have Contact type to do something with those items.

EntityCollection _ReqAttendees = _appointmentContext.GetAttributeValue<EntityCollection>("requiredattendees");
if ((_ReqAttendees != null) && (_ReqAttendees.Entities.Count > 0))
{
  foreach (var _party in _ReqAttendees.Entities)
  {
    if (_party.GetAttributeValue<EntityReference>("partyid").LogicalName == "contact")
    {
       // Do the work 
       // Contact ID : _party.GetAttributeValue<EntityReference>("partyid").Id
       
    }
  }
}

Hope this is helpful.