getSingleFieldDisplay example

public function viewField(FieldItemListInterface $items, $display_options = []) {
    /** @var \Drupal\Core\Entity\FieldableEntityInterface $entity */
    $entity = $items->getEntity();
    // If the field is not translatable and the entity is, then the field item     // list always points to the default translation of the entity. Attempt to     // fetch it in the current content language.     if (!$items->getFieldDefinition()->isTranslatable() && $entity->isTranslatable()) {
      $entity = $this->entityRepository->getTranslationFromContext($entity);
    }

    $field_name = $items->getFieldDefinition()->getName();
    $display = $this->getSingleFieldDisplay($entity, $field_name, $display_options);

    $output = [];
    $build = $display->build($entity);
    if (isset($build[$field_name])) {
      $output = $build[$field_name];
    }

    return $output;
  }

  /** * {@inheritdoc} */