public function finishView(FormView $view, FormInterface $form, array $options)
    {
        $data = $form->getData();
        if ($data instanceof InsertPagePagePart) {

            $this->validateParentPage();

            $reflections = [];
            $nodeFormView = $view->children['node'];
            /** @var ChoiceView $choice */
            foreach ($nodeFormView->vars['choices'] as $choice) {
                /** @var Node $currentData */
                $currentData = $choice->data;

                $entityCls = $currentData->getRefEntityName();
                if (!array_key_exists($entityCls, $reflections)) {
                    $reflections[$entityCls] = new \ReflectionClass($entityCls);
                }

                // only the pages with the right interface are selectable
                if (!$reflections[$entityCls]->implementsInterface(InsertablePageInterface::class)) {
                    $choice->attr['disabled'] = 'disabled';
                }
            }
        }
    }