4

 public class CollectionHandlerEventArgs : System.EventArgs
    {
        public string NameCollection { get; set; }
        public string ChangeCollection { get; set; }
        public Pair Pair { get; set; }

        public CollectionHandlerEventArgs(string collectionName, string changes, Pair pair)
        {
            NameCollection = collectionName;
            ChangeCollection = changes;
            Pair = pair;
        }

        public override string ToString()
        {
            return NameCollection + ", " + ChangeCollection + ", " + Pair;
        }
    }



public class MyCollection : Dictionary<int, Pair>
    {
        public string Name { get; set; }
        public delegate void CollectionHandler(object source, CollectionHandlerEventArgs args);

        // происходит при добавлении нового элемента или при удалении элемента из коллекции
        public event CollectionHandler CollectionCountChanged;

        public void Add(int key, Pair valuee)
        {
            OnCollectionChanged(this, new CollectionHandlerEventArgs(this.Name, "ADD", valuee));
            base.Add(key, valuee);
        }

        //обработчик события CollectionCountChanged
        public void OnCollectionChanged(object source, CollectionHandlerEventArgs args)
        {
            if (CollectionCountChanged != null)
                CollectionCountChanged(source, args);
        }
    }