BlockListController.php

<?php

namespace Drupal\block\Controller;

use Drupal\Core\Entity\Controller\EntityListController;
use Drupal\Core\Extension\ThemeHandlerInterface;
use Symfony\Component\HttpFoundation\Request;
use Symfony\Component\HttpKernel\Exception\NotFoundHttpException;

/**
 * Defines a controller to list blocks.
 */
class BlockListController extends EntityListController {
    
    /**
     * The theme handler.
     *
     * @var \Drupal\Core\Extension\ThemeHandlerInterface
     */
    protected $themeHandler;
    
    /**
     * Constructs the BlockListController.
     *
     * @param \Drupal\Core\Extension\ThemeHandlerInterface $theme_handler
     *   The theme handler.
     */
    public function __construct(ThemeHandlerInterface $theme_handler) {
        $this->themeHandler = $theme_handler;
    }
    
    /**
     * Shows the block administration page.
     *
     * @param string|null $theme
     *   Theme key of block list.
     * @param \Symfony\Component\HttpFoundation\Request $request
     *   The current request.
     *
     * @return array
     *   A render array as expected by
     *   \Drupal\Core\Render\RendererInterface::render().
     */
    public function listing($theme = NULL, ?Request $request = NULL) {
        $theme = $theme ?: $this->config('system.theme')
            ->get('default');
        if (!$this->themeHandler
            ->hasUi($theme)) {
            throw new NotFoundHttpException();
        }
        return $this->entityTypeManager()
            ->getListBuilder('block')
            ->render($theme, $request);
    }

}