title: DropDownList AppendDataBoundItems (first item to be blank and no duplicates)
body: <p>I have a <code>DropDownList</code> inside an <code>UpdatePanel</code> that is populated on postback from a <code>SqlDataSource</code>. It has a parameter which is another control. I sometimes need multiple postbacks, but what happens is that each time the update panel refreshes, items are added to the <code>DropDownList</code>. So the <code>DropDownList</code> ends up having data that is incorrect, or repeated data.</p>
  
  <p>I have the <code>AppendDataBoundItems</code> property set to <code>true</code> because I need the first item to be blank. </p>
  
  <p>How can I overcome this problem? Is there another way to have a blank first item?</p>
  
  <p>(This <code>DropDownList</code> is in an ASP.NET 2.0 web app, and codebehind is in C#)</p>