using System;

using System.Collections.ObjectModel;

​

​

namespace ConsoleApplication4

{

    /*--------------------------------------------------

    The custom class 'MyCustomCollection' inherits from 

    Collection and shows how you can override the InsertItem

    to check that an item that is being inserted into the collection

    meets some requirement (i.e. the string is not null

    ----------------------------------------------------*/

    public class Program

    {

        public static void Main(string[] args)

        {

            MyCustomCollection myCollection = new MyCustomCollection();

​

            // add items to the collection

            myCollection.Add("Joe");

            myCollection.Add("Jane");

​

            // adding a empty string will throw an exception

            myCollection.Add("");

        }

    }

​

​

    public class MyCustomCollection : Collection<string>

    {

        // Override the InsertItem method from Collection 

        //   and throw an error if the string being added is Null or Empty

        protected override void InsertItem(int index, string item)

        {

            // check if the item being added is null or empty

            if (string.IsNullOrEmpty(item))

            {

                throw new Exception("Item inserted into collection cannot be null.");

            }

​

            // perform the Collection classes InsertItem method

            base.InsertItem(index, item);

        }

    }

}

​