public function createComponentBuyItemForm()
    {
        $presenter = $this;
            return new \Nette\Application\UI\Multiplier(function($itemId) use ($presenter) {
                    $form = new Form();

                    $form->addText('quantity')
                ->addRule(Form::FILLED, "Počet kusů musí být vyplněn!")
                ->addRule(Form::INTEGER)
                ->setDefaultValue(1);

            $form->addSubmit('save', 'Přidat do košíku');
            $form->onSuccess[] = callback($presenter, 'buyItemFormSubmited');

            return $form;
        });
    }

    public function buyItemFormSubmited($form)
    {
        $id = $form->name;
        $quantity = $form->values->quantity;

        // ...
    }