xmlDoc.SelectSingleNode为什么选不中节点

[lsqsql]

XmlDocument xmlDoc = new XmlDocument();
xmlDoc.Load(Server.MapPath("wadl.xml"));
XmlElement root = xmlDoc.DocumentElement;
string nameSpace = root.NamespaceURI;
XmlNamespaceManager nsmgr = new XmlNamespaceManager(xmlDoc.NameTable);
nsmgr.AddNamespace("", nameSpace);
XmlNode rectifyele = xmlDoc.SelectSingleNode(@"application/resources", nsmgr);

问题是：rectifyele的值为什么为null？谢谢大家！！
附：wadl.xml

<?xml version="1.0" encoding="utf-8" ?>
- <application xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xsi:schemaLocation="http://research.sun.com/wadl/2006/10 wadl.xsd" xmlns="http://research.sun.com/wadl/2006/10">
- <resources base="http://somewhere.new/">
- <resource path="newRequest">
- <method name="GET">
- <request>
- <param name="newParam" type="xsd:string" style="query">
<doc xml:lang="en" title="newParam (Sample Value: newValue)">Estimated Type (supposed): [xsd:string]</doc>
</param>
</request>
</method>
</resource>
</resources>
</application>

[马老虎]

[xmlxslt]

把你的后两行改一下

nsmgr.AddNamespace("ya", nameSpace);
        XmlNode rectifyele = xmlDoc.SelectSingleNode(@"//ya:resources", nsmgr);

[psixm]

[Quote=引用 2 楼 xmlxslt 的回复:]
把你的后两行改一下
C# code
nsmgr.AddNamespace("ya", nameSpace);
XmlNode rectifyele = xmlDoc.SelectSingleNode(@"//ya:resources", nsmgr);
[/Quote]

AddNamespace里的前缀不能取空值么？
另外如果在这加了前缀，xml文件中要加相应的前缀么？还是加的这个前缀只限在C#这个源代码中使用？