/**
  * Handle the subscribed event.
  *
  * @param GetGroupHeaderEvent $event The event.
  *
  * @return void
  */
 public static function handle(GetGroupHeaderEvent $event)
 {
     if ($event->getValue() !== null) {
         return;
     }
     $handler = new static();
     $value = $handler->formatGroupHeader($event->getEnvironment(), $event->getModel(), $event->getGroupField(), $event->getGroupingMode(), $event->getGroupingLength());
     if ($value !== null) {
         $event->setValue($value);
     }
 }
 /**
  * Retrieve the arguments for the callback.
  *
  * @param GetGroupHeaderEvent $event The event being emitted.
  *
  * @return array
  */
 public function getArgs($event)
 {
     return array($event->getGroupField(), $event->getGroupingMode(), $event->getValue(), $event->getModel()->getPropertiesAsArray());
 }