title: How to register click event of button in GridView header with ajax UpdatePanel
body: <p>I have an UpdatePanel containing a GridView which contains a button in the HeaderTemplate of a TemplateField.  I want to add this button's click event to the UpdatePanel's trigger collection but this doesn't seem to work as I get an error message saying that a control with the specified ID could not be found.</p>
  
  <p>I thought of programmatically adding to the UpdatePanel's trigger collection on page load but this doesn't seem to be possible.</p>
  
  <p>Is there a work-around to this problem? I'd ideally like to keep my button within the header of the GridView. </p>