您可以从以下代码开始.当我执行它时，我得到正确的输出:

You may start with the following code. When I execute it, I get proper output:

string str = @"<?xml version='1.0' encoding='UTF-8'?><root><items><item id='W01MB154' href='01MB154.html' media-type='application/xhtml+xml' /><item id='W000Title' href='000Title.html' media-type='application/xhtml+xml' /></items><itemrefs><itemref idref='W000Title' /><itemref idref='W01MB154' /></itemrefs></root>";
XmlDocument xml = new XmlDocument();
xml.LoadXml(str);  // suppose that str string contains the XML data. You may load XML data from a file too.

XmlNodeList itemRefList = xml.GetElementsByTagName("itemref");
foreach (XmlNode xn in itemRefList)
{
    XmlNodeList itemList = xml.SelectNodes("//root/items/item[@id='" + xn.Attributes["idref"].Value + "']");
    Console.WriteLine(itemList[0].Attributes["href"].Value);
}

输出:

000Title.html

000Title.html

01MB154.html

01MB154.html

使用的XML是:

<?xml version='1.0' encoding='UTF-8'?>
<root>
    <items>
        <item id='W01MB154' href='01MB154.html' media-type='application/xhtml+xml' />
        <item id='W000Title' href='000Title.html' media-type='application/xhtml+xml' />
    </items>
    <itemrefs>
        <itemref idref='W000Title' />
        <itemref idref='W01MB154' />
    </itemrefs>
</root>

检查XML文档和XPath表达式的结构.

Check the structure of the XML document and the XPath expression.