MenuForm::buildOverviewForm

protected MenuForm::buildOverviewForm(array &$form, FormStateInterface $form_state)

protected function buildOverviewForm(array &$form, FormStateInterface $form_state) {
  // Ensure that menu_overview_form_submit() knows the parents of this form
  // section.
  if (!$form_state->has('menu_overview_form_parents')) {
    $form_state->set('menu_overview_form_parents', []);
  }

  $form['#attached']['library'][] = 'menu_ui/drupal.menu_ui.adminforms';

  $tree = $this->menuTree->load($this->entity->id(), new MenuTreeParameters());

  // We indicate that a menu administrator is running the menu access check.
  $this->getRequest()->attributes->set('_menu_admin', TRUE);
  $manipulators = array(
    array('callable' => 'menu.default_tree_manipulators:checkAccess'),
    array('callable' => 'menu.default_tree_manipulators:generateIndexAndSort'),
  );
  $tree = $this->menuTree->transform($tree, $manipulators);
  $this->getRequest()->attributes->set('_menu_admin', FALSE);

  // Determine the delta; the number of weights to be made available.
  $count = function(array $tree) {
    $sum = function($carry, MenuLinkTreeElement $item) {
      return $carry + $item->count();
    };
    return array_reduce($tree, $sum);
  };
  $delta = max($count($tree), 50);

  $form['links'] = array(
    '#type' => 'table',
    '#theme' => 'table__menu_overview',
    '#header' => array(
      $this->t('Menu link'),
      array(
        'data' => $this->t('Enabled'),
        'class' => array('checkbox'),
      ),
      $this->t('Weight'),
      array(
        'data' => $this->t('Operations'),
        'colspan' => 3,
      ),
    ),
    '#attributes' => array(
      'id' => 'menu-overview',
    ),
    '#tabledrag' => array(
      array(
        'action' => 'match',
        'relationship' => 'parent',
        'group' => 'menu-parent',
        'subgroup' => 'menu-parent',
        'source' => 'menu-id',
        'hidden' => TRUE,
        'limit' => \Drupal::menuTree()->maxDepth() - 1,
      ),
      array(
        'action' => 'order',
        'relationship' => 'sibling',
        'group' => 'menu-weight',
      ),
    ),
  );

  $form['links']['#empty'] = $this->t('There are no menu links yet. <a href=":url">Add link</a>.', [
    ':url' => $this->url('entity.menu.add_link_form', ['menu' => $this->entity->id()], [
      'query' => ['destination' => $this->entity->url('edit-form')],
    ]),
  ]);
  $links = $this->buildOverviewTreeForm($tree, $delta);
  foreach (Element::children($links) as $id) {
    if (isset($links[$id]['#item'])) {
      $element = $links[$id];

      $form['links'][$id]['#item'] = $element['#item'];

      // TableDrag: Mark the table row as draggable.
      $form['links'][$id]['#attributes'] = $element['#attributes'];
      $form['links'][$id]['#attributes']['class'][] = 'draggable';

      // TableDrag: Sort the table row according to its existing/configured weight.
      $form['links'][$id]['#weight'] = $element['#item']->link->getWeight();

      // Add special classes to be used for tabledrag.js.
      $element['parent']['#attributes']['class'] = array('menu-parent');
      $element['weight']['#attributes']['class'] = array('menu-weight');
      $element['id']['#attributes']['class'] = array('menu-id');

      $form['links'][$id]['title'] = array(
        array(
          '#theme' => 'indentation',
          '#size' => $element['#item']->depth - 1,
        ),
        $element['title'],
      );
      $form['links'][$id]['enabled'] = $element['enabled'];
      $form['links'][$id]['enabled']['#wrapper_attributes']['class'] = array('checkbox', 'menu-enabled');

      $form['links'][$id]['weight'] = $element['weight'];

      // Operations (dropbutton) column.
      $form['links'][$id]['operations'] = $element['operations'];

      $form['links'][$id]['id'] = $element['id'];
      $form['links'][$id]['parent'] = $element['parent'];
    }
  }

  return $form;
}