code: function() {
        inputEx.MultiSelectField.superclass.renderComponent.call(this);
        
        this.ddlist = new inputEx.widget.ListCustom({parentEl: this.fieldContainer,listSelectOptions: this.listSelectOptions, maxItems: this.maxItems, maxItemsAlert: this.maxItemsAlert });
        
     }
docs: renderComponent : override the MultiSelectField renderComponent function
  <ul>
  <li>Use the custom ddlist </li>
  <li>put options for select fields in the ddList Custom</li>
  </ul>