private void Button_Click(object sender, RoutedEventArgs e)
        {
            api AddShopListItemApi = new api();

            Shoppinglist shoppinglist = (Shoppinglist)shoppinglists.SelectedItem;
            Product      product      = finalProductList[productlist.SelectedIndex];

            MessageBox.Show(product.naam);
            MessageBox.Show(shoppinglist.Name);

            if (AddShopListItemApi.AddShoppinglistItem(shoppinglist.Id, product.Id))
            {
                MessageBox
                .Show("gelukt");
            }
            else
            {
                MessageBox.Show("nee");
            }
        }