KNPMenuBuilder, WIth Event how to order element => solution

MenuBuilder.php

<?php

namespace xxxx\Menu;

use Knp\Menu\FactoryInterface;
use Knp\Menu\ItemInterface;
use Symfony\Component\DependencyInjection\ContainerAware;
use xxx\Event\ConfigureMenuEvent;

class MenuBuilder extends ContainerAware
{
    public function build(FactoryInterface $factory)
    {
        $menu = $factory->createItem('root');

        $menu->addChild('Accueil', array(
            'route' => 'xxxxxx',
            'extras' => array(
                'order' => 70 //Use step of 10 is better for add element between 2 
            )
        ));

        //classic event solution
        $this->container->get('event_dispatcher')->dispatch(
            ConfigureMenuEvent::CONFIGURE,
            new ConfigureMenuEvent($factory, $menu)
        );

        //damn var useless but.. uasort need a reference
        $child = $menu->getChildren();
        uasort($child, array($this, 'sortMenu'));
        $menu->setChildren($child);

        return $menu;
    }

    protected function sortMenu($a, $b){
        /** @var ItemInterface $a */
        $aOrder = $a->getExtra('order');
        /** @var ItemInterface $b */
        $bOrder = $b->getExtra('order');

        if($aOrder === $bOrder){
            return 0;
        }

        return ($aOrder < $bOrder) ? -1 : 1;
    }
}