title: Sencha touche form validation
body: <p>I am creating my first app with sencha touch.
  I have a problem with form validation.
  This is the form:</p>
  
  <pre><code>var form = new Ext.form.FormPanel({
          title: 'Activity',
          items: [{
              xtype: 'fieldset',
              items: [{
                  xtype: 'textfield',
                  name : 'sector',
                  label: 'Sector',
                  required: true
              },
              {
                  xtype: 'selectfield',
                  name : 'city',
                  label: 'City',
                  options: [
                  {
                      text: '*',
                      value: '*'
                  },
                  {
                      text: 'First Option',  
                      value: 'first'
                  },
                  {
                      text: 'Second Option', 
                      value: 'second'
                  },
                  {
                      text: 'Third Option',  
                      value: 'third'
                  }]
              },
              {
                  xtype: 'textfield',
                  name : 'nation',
                  label: 'Nation',
                  required: true
              },
              {
                  xtype: 'toolbar',
                  docked: 'bottom',
                  layout: {
                      pack: 'center'
                  },
                  items: [{
                      xtype: 'button',
                      text: 'Cerca',
                      handler: function() {
                          formSettori.submit({
                              url: 'book.php',
                              method: 'GET',
                              success: function() {
                                  Ext.Msg.alert('OK');
                              },
                              failure: function() {
                                  Ext.Msg.alert('NO');
                              }
                          });
                      }
                  },
                  {
                      xtype: 'button',
                      text: 'Reset',
                      handler: function() {
                          form.reset();
                      }
                  }]
              }]
          }]
      });
  </code></pre>
  
  <p>the form has only three fields:
  -activities
  -city​​
  -nation</p>
  
  <p>all fields are required.
  activities and the nation must not be empty, while the city should not be equal to *</p>
  
  <p>how do I control the fields?
  thank you!</p>