title: How To Get Two-Way binding from RadioButton to title with ExtJS 6
body: <p>When I change the radiobutton value, I want the title to reflect the change. For textboxes, this works but not for radiobutton groups. I've got the code below and a fiddle example that shows it.</p>
  
  <p><a href="https://fiddle.sencha.com/#fiddle/1abr" rel="nofollow">https://fiddle.sencha.com/#fiddle/1abr</a></p>
  
  <pre><code>    Ext.define('MyApp.view.TestViewModel', {
          extend: 'Ext.app.ViewModel',
  
          alias: 'viewmodel.test', 
  
          data: {
              rg: 'BBB'
          }
      });
  
      Ext.define('MyApp.view.TestView', {
          extend: 'Ext.panel.Panel',
          layout: 'form',
  
  
          viewModel: {
              type: 'test'  // references alias "viewmodel.test"
          },
  
          bind: {
              title: 'Hello {rg}'
          },
  
  
          items: [{
              xtype: 'radiogroup',
              columns: 1,
              width: 600,
              horizontal: true,
              bind: {
                  value: {
                      rg: 'BBB'
                  }
              },
              items: [{
                  boxLabel: 'A',
                  inputValue: 'AAA',
                  name: 'rg'
              }, {
                  boxLabel: 'B',
                  inputValue: 'BBB',
                  name: 'rg'
              },{
                  boxLabel: 'C',
                  inputValue: 'CCC',
                  name: 'rg'
              }]
          }]
      });
  
      Ext.onReady(function () {
          Ext.create('MyApp.view.TestView', {
              renderTo: Ext.getBody(),
              width: 700
          });
      });
  </code></pre>