BookManager::addParentSelectFormElements

protected BookManager::addParentSelectFormElements(array $book_link)

protected function addParentSelectFormElements(array $book_link) {
  $config = $this->configFactory->get('book.settings');
  if ($config->get('override_parent_selector')) {
    return array();
  }
  // Offer a message or a drop-down to choose a different parent page.
  $form = array(
    '#type' => 'hidden',
    '#value' => -1,
    '#prefix' => '<div id="edit-book-plid-wrapper">',
    '#suffix' => '</div>',
  );

  if ($book_link['nid'] === $book_link['bid']) {
    // This is a book - at the top level.
    if ($book_link['original_bid'] === $book_link['bid']) {
      $form['#prefix'] .= '<em>' . $this->t('This is the top-level page in this book.') . '</em>';
    }
    else {
      $form['#prefix'] .= '<em>' . $this->t('This will be the top-level page in this book.') . '</em>';
    }
  }
  elseif (!$book_link['bid']) {
    $form['#prefix'] .= '<em>' . $this->t('No book selected.') . '</em>';
  }
  else {
    $form = array(
      '#type' => 'select',
      '#title' => $this->t('Parent item'),
      '#default_value' => $book_link['pid'],
      '#description' => $this->t('The parent page in the book. The maximum depth for a book and all child pages is @maxdepth. Some pages in the selected book may not be available as parents if selecting them would exceed this limit.', array('@maxdepth' => static::BOOK_MAX_DEPTH)),
      '#options' => $this->getTableOfContents($book_link['bid'], $book_link['parent_depth_limit'], array($book_link['nid'])),
      '#attributes' => array('class' => array('book-title-select')),
      '#prefix' => '<div id="edit-book-plid-wrapper">',
      '#suffix' => '</div>',
    );
  }
  $this->renderer->addCacheableDependency($form, $config);

  return $form;
}