using System;

using System.Collections.Generic;

​

public class Program

{

    public delegate void OnAddEventHandler(object item);

​

    public class AddEventArgs : EventArgs

    {

        public object item { get; set; }

    }

​

    public class MyList<T> : List<T>

    {

        public event OnAddEventHandler OnAdd;

        public new void Add(T item)

        {

            base.Add(item);

            if (OnAdd != null)

            {

                OnAdd(item);

            }

        }

    }

    public static void Main()

    {

        MyList<string> lst = new MyList<string>();

        lst.OnAdd += (item) => {

            Console.WriteLine("new item added: " + item);

        };

        lst.Add("test");

    }

}