如何将变量从子窗体传递到父symfony？

use Symfony\Contracts\EventDispatcher\Event;

class VariableEvent extends Event
{
    private $variable;

    public function __construct($variable)
    {
        $this->variable = $variable;
    }

    public function getVariable()
    {
        return $this->variable;
    }
}

use Symfony\Component\EventDispatcher\EventDispatcherInterface;

class ChildForm
{
    private $dispatcher;

    public function __construct(EventDispatcherInterface $dispatcher)
    {
        $this->dispatcher = $dispatcher;
    }

    public function submit()
    {
        // 假设 $variable 是要传递的变量
        $variable = 'example';

        $event = new VariableEvent($variable);
        $this->dispatcher->dispatch($event);
    }
}

use Symfony\Component\EventDispatcher\EventSubscriberInterface;

class ParentForm implements EventSubscriberInterface
{
    private $variable;

    public static function getSubscribedEvents()
    {
        return [
            VariableEvent::class => 'onVariableEvent',
        ];
    }

    public function onVariableEvent(VariableEvent $event)
    {
        $this->variable = $event->getVariable();
    }
}