buildFormActions example

  public function buildForm(array $form, FormStateInterface $form_state) {
    $parent_row_ids = ['parent_1', 'parent_2', 'parent_3'];
    $parent_rows = array_combine($parent_row_ids, $parent_row_ids);

    $form['table'] = $this->buildTestTable($parent_rows, 'tabledrag-test-parent-table', 'tabledrag-test-nested-parent', FALSE);

    $form['table']['#caption'] = $this->t('Parent table');
    $form['table'][reset($parent_row_ids)]['title'] = $this->buildTestTable() + ['#caption' => $this->t('Nested table')];

    $form['actions'] = $this->buildFormActions();

    return $form;
  }

}

    return $table;
  }

  /** * {@inheritdoc} */
  public function buildForm(array $form, FormStateInterface $form_state) {
    // Provide a default set of five rows.     $form['table'] = $this->buildTestTable();
    $form['actions'] = $this->buildFormActions();

    return $form;
  }

  /** * {@inheritdoc} */
  public function submitForm(array &$form, FormStateInterface $form_state) {
    $operation = isset($form_state->getTriggeringElement()['#op']) ?
      $form_state->getTriggeringElement()['#op'] :
      'save';