递归,这里用的是属性
 private static XmlNode SelectNodesByAttribute(XmlNode node)
        {
            //检测节点是否为空
            if (node == null)
            {
                return null;
            }
            
            //获取结点的数据
            if (node.Attributes != null)
            {
                //获取Attributes的值
            }            if (node.HasChildNodes)
            {
                return SelectNodesByAttribute(node.FirstChild);
            }
            else
            {
                if (node.NextSibling != null)
                {
                    node = node.NextSibling;
                }
                else
                {
                    while (node.ParentNode != null && node.NextSibling == null)
                    {
                        node = node.ParentNode;
                    }
                    node = node.NextSibling;
                }
                return SelectNodesByAttribute(node);
            }
        }