ViewsTestDataController.php

<?php

namespace Drupal\views_test_data\Controller;

use Drupal\Core\Security\TrustedCallbackInterface;

/**
 * Controller class for views_test_data callbacks.
 */
class ViewsTestDataController implements TrustedCallbackInterface {
    
    /**
     * Renders an error form page.
     *
     * This contains a form that will contain an error and an embedded view with
     * an exposed form.
     */
    public function errorFormPage() {
        $build = [];
        $build['view'] = [
            '#type' => 'view',
            '#name' => 'test_exposed_form_buttons',
        ];
        $build['error_form'] = \Drupal::formBuilder()->getForm('Drupal\\views_test_data\\Form\\ViewsTestDataErrorForm');
        return $build;
    }
    
    /**
     * #lazy_builder callback; for testing purposes only.
     */
    public static function placeholderLazyBuilder() {
        // No-op.
        return [];
    }
    
    /**
     * Test pre_render function.
     *
     * @param array $element
     *   A render array.
     *
     * @return array
     *   The changed render array.
     */
    public static function preRender($element) {
        $element['#markup'] = '\\Drupal\\views_test_data\\Controller\\ViewsTestDataController::preRender executed';
        return $element;
    }
    
    /**
     * {@inheritdoc}
     */
    public static function trustedCallbacks() {
        return [
            'placeholderLazyBuilder',
            'preRender',
        ];
    }

}