ConfirmDeleteMultiple::buildForm

public ConfirmDeleteMultiple::buildForm(array $form, FormStateInterface $form_state)

public function buildForm(array $form, FormStateInterface $form_state) {
  $edit = $form_state->getUserInput();

  $form['comments'] = array(
    '#prefix' => '<ul>',
    '#suffix' => '</ul>',
    '#tree' => TRUE,
  );
  // array_filter() returns only elements with actual values.
  $comment_counter = 0;
  $this->comments = $this->commentStorage->loadMultiple(array_keys(array_filter($edit['comments'])));
  foreach ($this->comments as $comment) {
    $cid = $comment->id();
    $form['comments'][$cid] = array(
      '#type' => 'hidden',
      '#value' => $cid,
      '#prefix' => '<li>',
      '#suffix' => Html::escape($comment->label()) . '</li>'
    );
    $comment_counter++;
  }
  $form['operation'] = array('#type' => 'hidden', '#value' => 'delete');

  if (!$comment_counter) {
    drupal_set_message($this->t('There do not appear to be any comments to delete, or your selected comment was deleted by another administrator.'));
    $form_state->setRedirect('comment.admin');
  }

  return parent::buildForm($form, $form_state);
}