Leo Antoli Solution to reto 2 MSDN defining add and remove http://blogs.msdn.com/b/esmsdn/archive/2014/09/19/retosmsdn-reto-2-161-esos-eventos.aspx

Reto.cs

// Leo Antoli solution to reto 2 MSDN using add and remove: http://blogs.msdn.com/b/esmsdn/archive/2014/09/19/retosmsdn-reto-2-161-esos-eventos.aspx

// NOTE: It's not thread-safe, locking should be added.

using System;
using System.Collections.Generic;
using System.Linq;

namespace Reto2ClassLibrary
{
    public class Reto2 : IReto2
    {
        private EventHandler handler;
        public event EventHandler EventFired
        {
            add {
                if (value.Target is Item) {
                    var list = handler == null ? new List<EventHandler>() 
                               : handler.GetInvocationList().OfType<EventHandler>().ToList();
                    foreach (var evt in list) {
                        handler -= evt;
                    }
                    list.Add(value);
                    foreach (var evt in list.OrderBy(x => (x.Target as Item).Index)) {   
                        handler += evt;
                    }
                }
            }

            remove {
               handler -= value;
            }
        }
        
        public void FireEvent() {
            if (handler != null) { 
                handler(this, EventArgs.Empty);
            }
        }
    }
}