View source  
  <?php
namespace Drupal\text_with_title\Plugin\Field\FieldFormatter;
use Drupal\Component\Utility\Html;
use Drupal\Core\Field\FieldItemListInterface;
use Drupal\Core\Field\FormatterBase;
use Drupal\Core\Form\FormStateInterface;
use Drupal\Core\Language\LanguageInterface;
class TextWithTitleTabsVerticalFormatter extends FormatterBase {
  
  public static function defaultSettings() {
    return [
      
      'tabs_width' => '3',
    ] + parent::defaultSettings();
  }
  
  public function settingsForm(array $form, FormStateInterface $form_state) {
    $element['tabs_width'] = [
      '#title' => $this
        ->t('Tabs Width'),
      '#type' => 'select',
      '#options' => [
        '1' => '1 Column',
        '2' => '2 Column',
        '3' => '3 Column',
        '4' => '4 Column',
        '5' => '5 Column',
        '6' => '6 Column',
        '7' => '7 Column',
        '8' => '8 Column',
        '9' => '9 Column',
        '10' => '10 Column',
        '11' => '11 Column',
        '12' => '12 Column',
      ],
      '#default_value' => $this
        ->getSetting('tabs_width'),
    ];
    return $element;
  }
  
  public function view(FieldItemListInterface $items, $langcode = NULL) {
    
    if (empty($langcode)) {
      $langcode = \Drupal::languageManager()
        ->getCurrentLanguage(LanguageInterface::TYPE_CONTENT)
        ->getId();
    }
    $elements = $this
      ->viewElements($items, $langcode);
    $build = [
      '#theme' => 'text_with_title_tabs_vertical',
      '#tabs' => $elements,
      '#tabs_width' => $this
        ->getSetting('tabs_width'),
    ];
    return $build;
  }
  
  public function viewElements(FieldItemListInterface $items, $langcode) {
    $elements = [];
    $id = Html::getUniqueId('bootstrap_tabs');
    foreach ($items as $delta => $item) {
      $elements[$delta] = [
        'title' => [
          '#plain_text' => $item->title,
        ],
        'active' => $delta == 0 ? TRUE : FALSE,
        'id' => $id . '--' . $delta,
        'text' => [
          '#type' => 'processed_text',
          '#text' => $item->text['value'],
          '#format' => $item->text['format'],
          '#langcode' => $langcode,
        ],
      ];
    }
    return $elements;
  }
}