NodePreviewController.php

<?php

namespace Drupal\node\Controller;

use Drupal\Core\Entity\Controller\EntityViewController;
use Drupal\Core\Entity\EntityInterface;
use Drupal\Core\Entity\EntityRepositoryInterface;
use Drupal\Core\Entity\EntityTypeManagerInterface;
use Drupal\Core\Render\RendererInterface;
use Symfony\Component\DependencyInjection\ContainerInterface;

/**
 * Defines a controller to render a single node in preview.
 */
class NodePreviewController extends EntityViewController {
    
    /**
     * The entity repository service.
     *
     * @var \Drupal\Core\Entity\EntityRepositoryInterface
     */
    protected $entityRepository;
    
    /**
     * Creates a NodeViewController object.
     *
     * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager
     *   The entity type manager.
     * @param \Drupal\Core\Render\RendererInterface $renderer
     *   The renderer service.
     * @param \Drupal\Core\Entity\EntityRepositoryInterface $entity_repository
     *   The entity repository.
     */
    public function __construct(EntityTypeManagerInterface $entity_type_manager, RendererInterface $renderer, EntityRepositoryInterface $entity_repository) {
        parent::__construct($entity_type_manager, $renderer);
        $this->entityRepository = $entity_repository;
    }
    
    /**
     * {@inheritdoc}
     */
    public static function create(ContainerInterface $container) {
        return new static($container->get('entity_type.manager'), $container->get('renderer'), $container->get('entity.repository'));
    }
    
    /**
     * {@inheritdoc}
     */
    public function view(EntityInterface $node_preview, $view_mode_id = 'full', $langcode = NULL) {
        $node_preview->preview_view_mode = $view_mode_id;
        $build = parent::view($node_preview, $view_mode_id);
        $build['#attached']['library'][] = 'node/drupal.node.preview';
        // Don't render cache previews.
        unset($build['#cache']);
        return $build;
    }
    
    /**
     * The _title_callback for the page that renders a single node in preview.
     *
     * @param \Drupal\Core\Entity\EntityInterface $node_preview
     *   The current node.
     *
     * @return string
     *   The page title.
     */
    public function title(EntityInterface $node_preview) {
        return $this->entityRepository
            ->getTranslationFromContext($node_preview)
            ->label();
    }

}