DefaultNegotiator.php

<?php

namespace Drupal\Core\Theme;

use Drupal\Core\Config\ConfigFactoryInterface;
use Drupal\Core\Routing\RouteMatchInterface;

/**
 * Determines the default theme of the site.
 */
class DefaultNegotiator implements ThemeNegotiatorInterface {
    
    /**
     * The system theme config object.
     *
     * @var \Drupal\Core\Config\ConfigFactoryInterface
     */
    protected $configFactory;
    
    /**
     * Constructs a DefaultNegotiator object.
     *
     * @param \Drupal\Core\Config\ConfigFactoryInterface $config_factory
     *   The config factory.
     */
    public function __construct(ConfigFactoryInterface $config_factory) {
        $this->configFactory = $config_factory;
    }
    
    /**
     * {@inheritdoc}
     */
    public function applies(RouteMatchInterface $route_match) {
        return TRUE;
    }
    
    /**
     * {@inheritdoc}
     */
    public function determineActiveTheme(RouteMatchInterface $route_match) {
        return $this->configFactory
            ->get('system.theme')
            ->get('default');
    }

}