循环访问 XML 元素[n] 子元素

我正在尝试遍历列表，但无法做到。

  public void SetShipmentsIndex(int shipmentId, string sourceShipmentIndex, IEnumerable<XElement> shipments)
  {
        var currentShipment = shipments.ToList()[shipmentId];
        foreach (var el in currentShipment)
        {
            if (el.Name == "sourceShipmentId")
            {
                el.SetValue(sourceShipmentIndex);
            }
            if (el.Name == "shipmentIndex")
            {
                el.SetValue(shipmentId);
            }
        }
    }

上面产生一个错误： foreach statement cannot operate on variables of type 'System.Xml.Linq.XElement' because 'System.Xml.Linq.XElement' does not contain a public definition for 'GetEnumerator'

shipments包含 3 个元素。

我试图通过他的后代shipments[shipmentId]和循环。我怎样才能做到这一点？

foreach (var el in currentShipment.Elements())
    {
        if (el.Name == "sourceShipmentId")
        {
            el.SetValue(sourceShipmentIndex);
        }
        if (el.Name == "shipmentIndex")
        {
            el.SetValue(shipmentId);
        }
    }