Sep 27 2006

.NET 2.0 Collections with generics - the basics

Posted by admin under .NET 2.0

I just created a simple tutorial on creating typesafe collections and adding (typesafe) sorting capabilities to it in .NET 1.x - now the time has come to .NET 2.0.

Some of the reasons at all for creating custom collections (instead of just using an ArrayList for example) 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, in .NET 2.0 - here's the easiest possible class and collection:

    

using System;
using System.Collections.Generic;

/// <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 LinkCollection  : System.Collections.Generic.List<Link> 
{

}

    The link class is taken from our .NET 1.1 tutorial - and the only difference is the LinkCollection class. While technically - we still need to inherit a base class ( but not CollectionBase ) - and we still have to implement a certain interface - we can let the compiler generate that code for us - that's what generics are about.

    The easiest way of understanding generics os to think like this: by specifying our inheritance from System.Collections.Generic.List<Link> the compiler is able to create typesafe functions (using class Link) for Add, IndexOf etc  - without us needing to see it.

    Now - all we need is to start using it - example of webform application:

    

    private LinkCollection GetCollList()
    {
        LinkCollection oColl = new LinkCollection();
        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);

        return oColl;

    }
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            Gridview1.DataSource = GetCollList();
            Gridview1.DataBind();
        }
    }