title: change active item in a card layout. ExtJS
body: <p>I have a panel using the card layout as follows:</p>
  
  <pre><code>var cardpanel = new Ext.Panel(
  {
      id: 'cardPanel',
      //title: 'Card Layout',
      region: 'center',
      layout: 'card',
      activeItem: 0,
      autoDestroy: false,
      bodyStyle: 'border-top:0px',
      defaults: {
          border: false
      },
      items: [mediaGrid, mappanel],
      tbar: [
          {
              id: 'card-media',
              text: 'Media',
              icon: '/img/silk/images.png',
              width: 50,
              handler: function () {
                  //switch to media
              }
          },
          {
              id: 'card-map',
              text: 'Map',
              icon: '/img/silk/map.png',
              width: 50,
              handler: function () {
                  //switch to map
              }
          }
      ]
  });
  </code></pre>
  
  <p>The commented parts are where i would like to implement the switch between the 2 panels in the card layout but im not sure how to do that. I've tried using setActiveItem but I was always either getting the setActiveItem is not a function or it it just didnt say anything.  How do i get it to switch panels?</p>