Suppose you want to extend a DataList and have it put out a div for each row. The RepeatLayout property can be either Flow (“Items are displayed without a table structure”) or Table (“Items are displayed in a table”). Since we want divs, we’re after RepeatLayout = RepeatLayout.Flow. Not so fast, though. This control isn’t that easy to extend.

What you get is a <span> which wraps the rest of the markup. More so, <div> rows are separated with superfluous <br>s that come out of nowhere!

<span id="foo">
    <div class="bar"></div>
    <br>
    <div class="bar"></div>
    <br>
    <div class="bar"></div>
    <br>
</span>

The first impulse is to override the TagKey property:

protected override HtmlTextWriterTag TagKey
{
  get { return HtmlTextWriterTag.Div; }
}

Just about every control will yield and render what you tell it, but not DataList. Beat your head against the wall—you still get a <span>. How weird is it to have an inline element wrap a block element!

My next guess was to look inside the ASP.NET CSS Friendly Control Adapters, but I was in for a disappointment. The DataListAdapter does not accommodate the “flow” layout. It merely produces a cleaner <table>. Back to the drawing board.

Eventually, I wrote my own, simple adapter:

namespace MyNamespace
{
  public class MyListControlAdapter : WebControlAdapter
  {
    protected override void RenderContents (HtmlTextWriter w)
    {
       DataList dataList = Control as DataList;

       if (dataList != null)
       {
          foreach (DataListItem li in dataList.Items)
              li.RenderControl (w);
       }
       else
       {
          base.RenderContents (w);
       }
    }
  }
}

which produced pristine markup:

<div id="foo">
   <div class="bar"></div>
   <div class="bar"></div>
   <div class="bar"></div>
</div>

Remember to create, or edit, a file named default.browser in the App_Browsers folder and add the following section:

<browsers>
  <browser refID="Default">
    <controlAdapters>
    <adapter
      controlType="MyNamespace.MyListControl"
      adapterType="MyNamespace.MyListControlAdapter" />
    </controlAdapters>
  </browser>
</browsers>

Hope this tip saves someone a day or two of head beating.