title: In server side, how to determine ModalPopupExtender is currently hidden?
body: <p>I have a page like that and the control structure is like that.</p>
  
  <ul>
  <li><code>UpdatePanel</code>
  <ul>
  <li><code>Button</code></li>
  <li><code>ModalPopupExtender</code></li>
  <li><code>ModalPopup Content Container</code></li>
  </ul></li>
  </ul>
  
  <p>Initially, <code>ModalPopup Content Container</code> is an empty control.</p>
  
  <p>After user clicks on the <code>Button</code>, a async postback will be triggered. During the postback, the server generates the content and appends to <code>ModalPopup Content Container</code>. Also sets the properties of <code>ModalPopupExtender</code>. Finally, calls <code>ModalPopupExtender.Show()</code> method and <code>UpdatePanel.Update()</code> method to show the modal popup.</p>
  
  <p>This method works fine if all controls in <code>ModalPopup Content Container</code> contains simple control. If a control is a button that needs to postback to server side, that is a problem.</p>
  
  <p>Since the controls in <code>ModalPopup Content Container</code> is dynamically created. If a control in <code>ModalPopup Content Container</code> triggers a postback event, the control must be created before <code>RaisePostBackEvent</code> is called in server side.</p>
  
  <p>My idea is to determine whether the <code>ModalPopupExtender</code> is hidden or shown in client side in order to re-generate the dynamic control in <code>ModalPopup Content Container</code>.</p>
  
  <p>So my question is how to determine a <code>ModalPopupExtender</code> is hidden or shown.</p>
  
  <p>Of coz, if you think my method does not work at all, please give me some suggestions. Thanks!</p>