title: extjs4 Change action column icon dynamically
body: <p>I'm using <code>getClass</code> to render the icon in the action column.  </p>
  
  <pre><code>{
  xtype: 'actioncolumn',
  id:'actionColumnGridUsers',
  width: 30,
  hideable: false,
  items: ['-&gt;',
      {
          getClass: function (v, meta, rec)
          {
              if (rec.get('nameUser') != '') return 'icon-edit';
              else return 'icon-add';
          }
  
      }
  }
  </code></pre>
  
  <p>And the css code:  </p>
  
  <pre><code>.icon-add { background-image: url("../images/add.png"); }
  .icon-edit { background-image: url("../images/edit.png"); }
  </code></pre>
  
  <p>The code seems to be correct, but the icon is not shown. What I'm missing?</p>