code: function() {
          var fields = this.form.getFields().items,
              f,
              fLen   = fields.length;
  
          for (f = 0; f < fLen; f++) {
              fields[f].checkChange();
          }
      }
docs: Forces each field within the form panel to
  {@link Ext.form.field.Field#checkChange check if its value has changed}.