ViewsUiTestHooks.php

<?php

declare (strict_types=1);
namespace Drupal\views_ui_test\Hook;

use Drupal\Core\Hook\Attribute\Hook;

/**
 * Hook implementations for views_ui_test.
 */
class ViewsUiTestHooks {
    
    /**
     * Implements hook_views_preview_info_alter().
     *
     * Add a row count row to the live preview area.
     */
    public function viewsPreviewInfoAlter(&$rows, $view) {
        $data = [
            '#markup' => t('Test row count'),
        ];
        $data['#attached']['library'][] = 'views_ui_test/views_ui_test.test';
        $rows['query'][] = [
            [
                'data' => $data,
            ],
            count($view->result),
        ];
    }

}