TestThemeNegotiator.php

<?php

declare (strict_types=1);
namespace Drupal\menu_test\Theme;

use Drupal\Core\Routing\RouteMatchInterface;
use Drupal\Core\Theme\ThemeNegotiatorInterface;

/**
 * Tests the theme negotiation functionality.
 *
 * Retrieves the theme key of the theme to use for the current request based on
 * the theme name provided in the URL.
 */
class TestThemeNegotiator implements ThemeNegotiatorInterface {
  
  /**
   * {@inheritdoc}
   */
  public function applies(RouteMatchInterface $route_match) {
    return (bool) $route_match->getParameter('inherited');
  }
  
  /**
   * {@inheritdoc}
   */
  public function determineActiveTheme(RouteMatchInterface $route_match) {
    $argument = $route_match->getParameter('inherited');
    // Test using the variable administrative theme.
    if ($argument == 'use-admin-theme') {
      return \Drupal::config('system.theme')->get('admin');
    }
    elseif ($argument == 'use-test-theme') {
      return 'test_theme';
    }
    elseif ($argument == 'use-fake-theme') {
      return 'fake_theme';
    }
    // For any other value of the URL argument, do not return anything. This
    // allows us to test that returning nothing from a theme negotiation
    // causes the page to correctly fall back on using the main site theme.
  }

}