XML中加入namespace

实际的显示效果是这样的

<?xml version="1.0" encoding="GB2312"?>
<document xmlns:bbs="http://www.baidu.com/search/bbs_sitemap.xsd">
<webSite>bbs.diaoyu.com</webSite>
<webMaster>pengzhijie@tiexue.net</webMaster>
<updatePeri>0.5</updatePeri>
<updatetime>2012/11/16 00:00:00</updatetime>
<version>钓鱼之家论坛</version>
<item>
<link>http://bbs.diaoyu.com/showtopic-2585.aspx</link>
<title>化氏秘籍</title>
<pubDate>2012-11-13 18:13:08</pubDate>
<bbs:lastDate>2012-11-16 10:09:08</bbs:lastDate>
<bbs:reply>4</bbs:reply>
<bbs:hit>1</bbs:hit>
<bbs:mainLen>187</bbs:mainLen>
<bbs:boardid>2</bbs:boardid>
<bbs:pick>0</bbs:pick>
</item>
</document>

XDocument xdoc = new XDocument();
            xdoc.Declaration = new XDeclaration("1.0", "GB2312","yes");
            XElement root = new XElement("document", new XAttribute(XNamespace.Xmlns+"bbs", "http://www.baidu.com/search/bbs_sitemap.xsd"));

private static XElement GetItem(TopicInfo data)
        {
            XNamespace xn = "http://www.baidu.com/search/bbs_sitemap.xsd";

            byte[] MessageByte = System.Text.Encoding.Default.GetBytes(data.Message);
            int len = MessageByte.Length;
            int pick = Convert.ToInt32(data.Digest) > 0 ? 1 : 0;
            XElement item = new XElement("item",
                new XElement("link", "http://bbs.diaoyu.com/showtopic-2585.aspx"),
                new XElement("title",data.Title),
                new XElement("pubDate", data.PostDateTime.ToString("yyyy-MM-dd HH:mm:ss")),
                new XElement(xn+"lastDate", data.LastPost.ToString("yyyy-MM-dd HH:mm:ss")),
                new XElement(xn+"reply",data.Replies),
                new XElement (xn+"hit",data.Views),
                new XElement(xn+"mainLen",len),
                new XElement(xn+"boardid",data.Fid),
                new XElement(xn+"pick",pick)
                );
            return item;
        }

显示的结果就是在每个加了”xn“的XElement，前面会显示bbs:,如果把

new XAttribute(XNamespace.Xmlns+"bbs", "http://www.baidu.com/search/bbs_sitemap.xsd")中的bbs改成别的，那么那些加了”xn“的XElement会显示更改之后的namespace