title: Updating a control outside the UpdatePanel
body: <p>So I have a <code>UserControl</code> with some cascading <code>DropDownList</code>s on it.  Selecting from list 1 enables list 2, which in turn enables list 3.  Once you've made a selection in all three lists, you can move to the next page.</p>
  
  <p>The <code>DropDownList</code>s are all inside an <code>UpdatePanel</code>.  But the "Next Page" button is outside the <code>UpdatePanel</code>.  That button should be disabled until all three lists have a selection, and then it should be enabled again.  But since the button is outside the <code>UpdatePanel</code>, it doesn't update when I make selections.  (<strong>Edit</strong>: The "Next Page" button is on a page that also contains the <code>UserControl</code>.)</p>
  
  <p>I know one way to resolve this:</p>
  
  <pre><code>var scriptManager = ScriptManager.GetCurrent(this.Page);
  scriptManager.RegisterPostBackControl(dropDownList1);
  scriptManager.RegisterPostBackControl(dropDownList2);
  scriptManager.RegisterPostBackControl(dropDownList3);
  </code></pre>
  
  <p>This ensures a postback when any dropdown list is changed, so that the button can update.  But if I do this, I might as simplify by getting rid of the <code>UpdatePanel</code> in the first place.</p>
  
  <p>Is there another way, through some clever JavaScript or something, that I can update a control outside an <code>UpdatePanel</code> without having to give up Ajax?</p>