title: trigger a function to run when a carousel's page is changed in Sencha Touch
body: <p>I'm not sure how many people on here have used the Sencha Touch js library, but I have a question that MUST be simple despite my many attempts and fails.
  Basically, I have a carousel which pages through results as you swipe, and I want to trigger a function each time a new page is shown.<br>
  Anyone have any idea how to do this?  I've tried adding a listener to it, and for some reason that doesn't work.
  Something like this:</p>
  
  <pre><code>var apCarousel = new Ext.Carousel({
              direction: 'horizontal',
              activeItem: 0,
              ui: 'dark',
              itemId  :   "apCarousel",
              items: pageItems,
              listeners   :   {
                  click   :   {
                      element :   this,
                      fn  :   function(){alert('yo!');}
                  }
              }
          });
  </code></pre>
  
  <p>Any help would be greatly appreciated.
  Thanks.</p>