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) : void {
    $data = [
      '#markup' => 'Test row count',
    ];
    $data['#attached']['library'][] = 'views_ui_test/views_ui_test.test';
    $rows['query'][] = [
      [
        'data' => $data,
      ],
      count($view->result),
    ];
  }

}