如何在'woocommerce_after_order_notes‘中设置类属性，然后在'woocommerce_checkout_process’中使用它？

add_action('woocommerce_after_order_notes', 'set_custom_attribute');

function set_custom_attribute($checkout)
{
    echo '<div id="custom_checkout_field">';
    
    woocommerce_form_field('custom_attribute', array(
        'type' => 'text',
        'class' => array('my-field-class form-row-wide'),
        'label' => __('Custom Attribute'),
        'placeholder' => __('Enter custom attribute'),
        'required' => true,
    ), $checkout->get_value('custom_attribute'));
    
    echo '</div>';
}

add_action('woocommerce_checkout_process', 'process_custom_attribute');

function process_custom_attribute()
{
    if (empty($_POST['custom_attribute'])) {
        wc_add_notice(__('Please enter a value for the custom attribute.'), 'error');
    } else {
        $custom_attribute = sanitize_text_field($_POST['custom_attribute']);
        
        // 在这里使用类属性，例如保存到订单元数据中
        // $order_id = wc_get_order_id_by_order_key($_POST['order_key']);
        // update_post_meta($order_id, 'custom_attribute', $custom_attribute);
    }
}