ASP.NET

public class ListBox : System.Web.UI.WebControls.WebControl
{
    //...
    private ListItemDataCollection listData = null;
    public ListItemDataCollection ListItems
    {
        get
        {
            if (listData == null)
            {
                listData = new ListItemDataCollection();
            }
            return listData;
        }
    }

    protected override void Render(HtmlTextWriter output)
    {
        // properties
        if (Rows > 1)
        {
            output.AddAttribute(HtmlTextWriterAttribute.Size, Rows.ToString());
            if (MultipleSelections)
                output.AddAttribute(HtmlTextWriterAttribute.Multiple, true.ToString());
        }

        // calls the base method
        base.Render(output);
    }

    protected override void CreateChildControls()
    {
        Controls.Clear();
        for (int i =0; i < ListItems.Count; i++)
        {
            //ListItemData item = ListItems[i];
            //Controls.Add(new ListItem(item.Text, item.Value, i == SelectedIndex));
            Controls.Add(ListItems[i]);
        }
    }

    public override ControlCollection Controls
    {
        get
        {
            EnsureChildControls();
            return base.Controls;
        }
    }
}

    [ToolboxItem(false),
    ToolboxData("<{0}:ListItem runat=server>"),
    TypeConverter(typeof(ExpandableObjectConverter))]
    public class ListItem : System.Web.UI.Control
    {
        public ListItem(string text, string value)
            : base()
        {
            Text = text;
            Value = value;
        }
        public ListItem() { }

        public ListItem(string text, string value, bool selected)
            : this(text, value)
        {
            Selected = selected;
        }
        #endregion

        public string Text
        {
            get
            {
                object text = ViewState["Text"];
                if (text == null)
                    return string.Empty;
                return (string)text;
            }
            set
            {
                ViewState["Text"] = value;
            }
        }

        public string Value
        {
            get
            {
                object value = ViewState["Value"];
                if (value == null)
                    return string.Empty;
                return (string)value;
            }
            set
            {
                ViewState["Value"] = value;
            }
        }

        [EditorBrowsable(EditorBrowsableState.Never)]
        public bool Selected
        {
            get
            {
                object selected = ViewState["Selected"];
                if (selected == null)
                    return false;
                return (bool)selected;
            }
            set
            {
                ViewState["Selected"] = value;
            }
        }

        protected override void Render(HtmlTextWriter writer)
        {
            base.Render(writer);

            writer.AddAttribute(HtmlTextWriterAttribute.Value, Value);
            if (Selected)
                writer.AddAttribute(HtmlTextWriterAttribute.Selected, true.ToString());

            writer.RenderBeginTag(HtmlTextWriterTag.Option);
            writer.Write(Text);
            writer.RenderEndTag();
        }
    }

    public sealed class ListItemDataCollection : List<listitem>{}
</listitem>