public interface IDefaultEventView
    {
        MyEvent EventItem { get; set; }
        StringBuilder CreateEventOutput();
    }

  public class ConnectDeviceEventView : IDefaultEventView
    {
        public MyEvent EventItem { get; set; }

        public StringBuilder CreateEventOutput()
        {
            var sb = new StringBuilder();
            sb.AppendFormat("<b>{0}</b>",EventItem.Description);
            return sb;
        }
    }

 public class DefaultEventView : IDefaultEventView
    {
        public MyEvent EventItem { get; set; }

        public StringBuilder CreateEventOutput()
        {
            var sb = new StringBuilder();
            sb.AppendLine(EventItem.Description);
            return sb;
        }
    }

 private static void WriteEventView(HttpResponse stream, IDefaultEventView viewer)
        {
            var sb = viewer.CreateEventOutput();
            var sr = new StringReader(sb.ToString());
            do
            {
                string line = sr.ReadLine();
                stream.Write(line);
                stream.Write("\r\n");
                stream.Flush();
            }
            while (sr.Peek() != -1);
            sr.Close();
        }

 public class EventViewFactory
    {
        public MyEvent EventItem { get; set; }

        public EventViewFactory(MyEvent eventItem)
        {
            EventItem = eventItem;
        }

        public IDefaultEventView ViewerInstance()
        {
            IDefaultEventView result;
            if (EventItem.EventType == 2)
            {
                result= new ConnectDeviceEventView();
            }
            else
            {
                result= new DefaultEventView();
            }
            return result;
        }
    }

  static void Main(string[] args)
        {
            var event1 = new MyEvent() { EventType = 2 };
            var factory = new EventViewFactory(event1);
            HttpResponse stream = new HttpResponse(null);// закрываем глаза на это :)
            WriteEventView(stream, factory.ViewerInstance());
        }