Jul 04 2004

Collections and sorting in C#

Posted by admin under .NET

 

This article is intended for .NET 1.1. In version 2.0 I advise you to use generics instead of inheriting from CollectionBase - an article on that will be available (later) as well. 

Some of the main goals when creating a custom collection (instead of just using for example ArrayList ) are  

  • type safety (you should only be able to insert objects of a certain type)
  • incapsulation - you might for example create an ReadFromDatabase function inside the collection class
  • still - we want to be able to use "regular" iterator functions - such as foreach etc

So - here the easiest possible class and collection:



using System;
using System.Data;
using System.Collections;

namespace colltest
{
	/// <summary>
	/// Summary description for Link.
	/// </summary>
	public class Link
	{
		private string m_strUrl = "";
		private string m_strName = "";
		public string Url
		{
			get
			{
				return m_strUrl;
			}
			set
			{
				m_strUrl = value;
			}
		}
		public string Name
		{
			get
			{
				return m_strName;
			}
			set
			{
				m_strName = value;
			}
		}
		public Link()
		{
		}
	}

	public class LinkColl : CollectionBase	
	{
		public Link this[int nIndex]
		{
			get { return (Link) base.List[nIndex]; }
		}

		#region Methods
		public void Add(Link tab)
		{
			//Kolla s den inte redan finns
			base.List.Add(tab);
		}
	
		public int IndexOf(Link tab)
		{
			return base.List.IndexOf(tab);
		}
		#endregion

	}
}

So the key for our collection class is to derive from CollectionBase. We then override

public Link this[int nIndex]

and

public void Add(Link tab)

and

public int IndexOf(Link tab)

and that's all we need. Now we are able to write code such as:



			LinkColl oColl = new LinkColl();

			Link oNew = new Link();
			oNew.Name = "ASPCode";
			oNew.Url = "http://www.aspcode.net";
			oColl.Add( oNew );

			oNew = new Link();
			oNew.Name = "ASP.NET";
			oNew.Url = "http://www.asp.net";
			oColl.Add( oNew );

			oNew = new Link();
			oNew.Name = "411asp.net";
			oNew.Url = "http://www.411asp.net";
			oColl.Add( oNew );

			foreach( Link oLink in oColl )
			{
				Console.WriteLine( oLink.Name + ":" + oLink.Url );
			}

 

Download is available in part 4