使用XmlDocument.SelectNodes遍历xml元素遇到的一个XPathException

使用XmlDocument类时候报错：

未处理的XPathException：
需要命名空间管理器或 XsltContext。此查询具有前缀、变量或用户定义的函数。

需要使用XmlNamespaceManager类：Resolves, adds, and removes namespaces to a collection and provides scope management for these namespaces.

这是因为使用的soap文档含有自己的命名空间。相同问题：http://bbs.csdn.net/topics/350101606

最终修改后的代码：

 string soap = "";
                    soap += "<SOAP-ENV:Envelope xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/">";
                    soap += "<SOAP-ENV:Body>";
                    soap += "<AP-MSG:SubscriptionRequest xmlns:AP-MSG="http://www.vestas.dk/2001/04/ap" xmlns:SOAP-ENC="http://schemas.xmlsoap.org/soap/encoding/">";
                    soap += "<RequestBase ClientRequestHandle="41" ReturnItemTime="false" ReturnItemName="true" CallbackURL="10.116.21.222:1055" CallbackRate="PT10S"/>";
                    soap += "<ItemRequestSpec MaxAge="PT0.1S"/>";
                    soap += "<ItemList>";
                    foreach (IoTag tag in Tags)
                    {
                        soap += string.Format("<Item ItemName="{0}"/>", tag.Name);
                    }
                    soap += "</ItemList>";
                    soap += "</AP-MSG:SubscriptionRequest>";
                    soap += "</SOAP-ENV:Body>";
                    soap += "</SOAP-ENV:Envelope>";
                    string subscriptionRequest = "";
                    subscriptionRequest += "POST * HTTP/1.1
";
                    subscriptionRequest += "Content-Type:text/xml;charset=ISO-8859-1
";
                    subscriptionRequest += "Connection:Keep-Alive
";
                    subscriptionRequest += "SOAPAction:http://www.vestas.dk/2001/04/ap#SubscriptionRequest
";
                    subscriptionRequest += string.Format("Content-Length:{0}
", soap.Length);
                    subscriptionRequest += "
";
                    subscriptionRequest += soap;

                    XmlDocument xDoc = new XmlDocument();
                    xDoc.LoadXml(soap);
                    XmlNamespaceManager nsMgr = new XmlNamespaceManager(xDoc.NameTable);
                    nsMgr.AddNamespace("SOAP-ENV", "http://schemas.xmlsoap.org/soap/envelope/");
                    nsMgr.AddNamespace("AP-MSG", "http://www.vestas.dk/2001/04/ap");
                    nsMgr.AddNamespace("SOAP-ENC", "http://schemas.xmlsoap.org/soap/encoding/");
                    XmlElement xe = xDoc.DocumentElement;
                    XmlNodeList xnl = xDoc.SelectNodes("/SOAP-ENV:Envelope/SOAP-ENV:Body/AP-MSG:SubscriptionRequest/ItemList/Item", nsMgr);

　　　　　　　　　　　　foreach (XmlNode item in xnl)
                    {
                        string s = item.Attributes["ItemName"].Value;
                    }