title: ExtJS 4: A grid column that displays checkbox with checkall header and can be hidden
body: <p>We are using ExtJS 4.2, so that is my context for this question.</p>
  
  <p>I need to have a column in a grid that:</p>
  
  <ol>
  <li>Display a checkbox on each row which can be selected/deselected. It is for the purpose of tracking user selections and not synchronized with underlying store data.</li>
  <li>Has a checkall checkbox in header that allows user to select or deselect all rows in the grid.</li>
  <li>Can be hidden/removed based on certain condition when page is rendered (user permission or data).</li>
  </ol>
  
  <p>I tried the following:</p>
  
  <ol>
  <li><p>SelModel - which will satisfy requirement No. 2, but cannot be manipulated once defined (see <a href="http://www.sencha.com/forum/showthre...selectionModel" rel="nofollow">http://www.sencha.com/forum/showthre...selectionModel</a>).</p></li>
  <li><p>CheckColumn - which satisfies requirement No. 3, but doesn't have a checkall box in column header (see <a href="http://www.sencha.com/forum/showthread.php?265924" rel="nofollow">http://www.sencha.com/forum/showthread.php?265924</a>).</p></li>
  </ol>
  
  <p>Is there a way for me to achieve what I wanted?</p>
  
  <p>Thanks in advance</p>
  
  <p>Haixi</p>