title: listener for radiobutton
body: <p>I want to add 3 radiobuttons in a toolbar like this:</p>
  
  <pre><code>dockedItems: [
              {
                  xtype: 'toolbar',
                  dock: 'top',
                  items: [
                      {
                          xtype: 'radiogroup',
                          width: 500,
                          fieldLabel: 'Show',
                          items: [
                              {
                                  xtype: 'radiofield',
                                  id: 'all',
                                  name: 'show',
                                  boxLabel: 'All vehicles',
                                  checked: true
                              },
                              {
                                  xtype: 'radiofield',
                                  id: 'online',
                                  name: 'show',
                                  boxLabel: 'Online vehicles'
                              },
                              {
                                  xtype: 'radiofield',
                                  id: 'offline',
                                  name: 'show',
                                  boxLabel: 'Offline vehicles'
                              }
                          ]
                      }
                  ]
              }
          ]
  </code></pre>
  
  <p>I want to use a listener for these buttons. When someone clicks on offline i want to load internals.load({url:internals/offline.json});</p>
  
  <p>i just can't get it working. Any advice/help?</p>
  
  <p>Thanks</p>