TestDomainObjectViewSubscriber.php

<?php

namespace Drupal\early_rendering_controller_test;

use Symfony\Component\EventDispatcher\EventSubscriberInterface;
use Symfony\Component\HttpFoundation\Response;
use Symfony\Component\HttpKernel\Event\ViewEvent;
use Symfony\Component\HttpKernel\KernelEvents;

/**
 * View subscriber for turning TestDomainObject objects into Response objects.
 */
class TestDomainObjectViewSubscriber implements EventSubscriberInterface {
    
    /**
     * Sets a response given a TestDomainObject instance.
     *
     * @param \Symfony\Component\HttpKernel\Event\ViewEvent $event
     *   The event to process.
     */
    public function onViewTestDomainObject(ViewEvent $event) {
        $result = $event->getControllerResult();
        if ($result instanceof TestDomainObject) {
            if ($result instanceof AttachmentsTestDomainObject) {
                $event->setResponse(new AttachmentsTestResponse('AttachmentsTestDomainObject'));
            }
            elseif ($result instanceof CacheableTestDomainObject) {
                $event->setResponse(new CacheableTestResponse('CacheableTestDomainObject'));
            }
            else {
                $event->setResponse(new Response('TestDomainObject'));
            }
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public static function getSubscribedEvents() : array {
        $events[KernelEvents::VIEW][] = [
            'onViewTestDomainObject',
        ];
        return $events;
    }

}