碰巧的是，我昨天刚刚在博客上写了这件事，想知道如何add a subscribe to mailing list checkbox. 关键点是：

查看WooCommerce tutorial

class WooSubscribeCheckbox {

    // add hooks into WooCommerce
    public static function run() {
        add_filter(\'woocommerce_checkout_fields\',
            array(__CLASS__, \'filterWooCheckoutFields\'));

        add_action(\'woocommerce_checkout_update_order_meta\',
            array(__CLASS__, \'actionWooCheckoutUpdateOrderMeta\'));

        add_filter(\'woocommerce_email_order_meta_keys\',
            array(__CLASS__, \'filterWooEmailOrderMetaKeys\'));
    }

    /**
    * add custom fields to WooCommerce checkout
    * @param array fields
    * @return array
    */
    public static function filterWooCheckoutFields($fields) {
        global $woocommerce;

        // add field at end of billing fields section
        $fields[\'billing\'][\'our_mailing_subscribe\'] = array(
            \'type\' => \'checkbox\',
            \'label\' => \'Subscribe to mailing list?\',
            \'placeholder\' => \'Subscribe to mailing list\',
            \'required\' => false,
            \'class\' => array(),
            \'label_class\' => array(),
        );

        return $fields;
    }

    /**
    * save custom order fields
    * @param int $order_id
    */
    public static function actionWooCheckoutUpdateOrderMeta($order_id) {
        if (isset($_POST[\'our_mailing_subscribe\'])) {
            update_post_meta($order_id, \'Subscribe to mailing list\',
                stripslashes($_POST[\'our_mailing_subscribe\']));
        }
    }

    /**
    * add our custom fields to WooCommerce order emails
    * @param array $keys
    * @return array
    */
    public static function filterWooEmailOrderMetaKeys($keys) {
        $keys[] = \'Subscribe to mailing list\';

        return $keys;
    }

}

WooSubscribeCheckbox::run();