title: Overlay is not coming on tap of image in sencha touch2
body: <p>i want to show overlay on tap of image. but it is not showing. what is the mistakes in my code. can any one tell me how to show overlay on tap of image.</p>
  
  <p>Here is my code:</p>
  
  <pre><code>  {
        xtype: 'image',
        src: 'http://www.veryicon.com/icon/preview/System/Colored%20Developers%20Button/question%20Yellow%20Icon.jpg',
        listeners: {
                   tap: function () {
                    var popup = Ext.create('Ext.Panel', {
                    modal: true,
                    centered: true,
                    width: 300,
                    height: 400,
                    layout: 'fit',                                                                
                    scrollable: true
                   });
                  popup.show();
                 }
                },
         height: 32,
         width: 32
      }
  </code></pre>