The first thing I did was create my own control that inherits from CheckboxList. The table-based output of the standard checkbox list is harder to style, and in general I like to used unordered lists wherever possible, so I followed this simple method for overloading the Render method and making my own output as an <ul> and each selection as a <li>. The example Chris Pollock gives is in VB, below is my loose adaptation in C#.

protected override void Render(System.Web.UI.HtmlTextWriter writer)
{
string inputFormatString = "<input id=\"{0}\" name=\"{1}\" type=\"checkbox\" value=\"{2}\" {3} {4} />";
string labelFormatString = "{1}";
if (!string.IsNullOrEmpty(this.CssClass))
writer.WriteLine("<ul class=\"" + this.CssClass + "\">");
else
writer.WriteLine("<ul>");
for (int i = 0; i < Items.Count; i++)
{
string postbackScript = "";
if(this.AutoPostBack)
{
postbackScript = String.Format("onclick=\"javascript:setTimeout('__doPostBack(\'{0}\',\'\')', 0)\"", this.UniqueID + "$" + i.ToString());
}
string itemChecked = "";
if(Items[i].Selected)
{
itemChecked = "checked=\"checked\"";
}
writer.WriteLine("<li>");
writer.WriteLine(string.Format(inputFormatString, this.ClientID + "_" + i.ToString(), this.UniqueID + "$" + i.ToString(), Items[i].Value, itemChecked, postbackScript));
writer.WriteLine(string.Format(labelFormatString, this.ClientID + "_" + i.ToString(), Items[i].Text));
writer.WriteLine("</li>");
}
writer.WriteLine("</ul>");
}

It’s a nice start, but it doesn’t solve my problem of adding headings to the list. I could go pretty far into making this CheckBoxList control really custom so that it accepts a heirarchical data source, but i decided that would be good for another time. I simply decided to create an event on the CheckBoxList that would be called before each item renders.

public delegate void ItemPreRenderHandler(System.Collections.IEnumerable data, int index, ListItem item, System.Web.UI.HtmlTextWriter writer);
public event ItemPreRenderHandler ItemPreRender;
public void OnItemPreRender(System.Collections.IEnumerable data, int index, ListItem item, System.Web.UI.HtmlTextWriter writer)
{
if (ItemPreRender != null)
{
ItemPreRender(data, index, item, writer);
}
}


And call OnItemPreRender in the Render method as the first command in the for loop for each item.

OnItemPreRender(((System.Collections.IEnumerable)this.DataSource), i ,Items[i], writer);

With this, on the page using the control, I hooked a method up to the Event that checked to see if the ‘Category’ was different than the last item, and if so output an <li> with a heading. Very old school, but rather simple and flexible.