包含名称空间的XDocument

试试这个，对我有用

    XNamespace nsSys = "http://schemas.microsoft.com/2004/06/windows/eventlog/system";    XElement xEl2 = xDoc.Element(nsSys + "System");    XElement xEl3 = xEl2.Element(nsSys + "Correlation");    XAttribute xAtt1 = xEl3.Attribute("ActivityID");    String sValue = xAtt1.Value;

您需要使用命名空间。

完整的审判资料

        public static void Main()        { XElement xDoc = XElement.Parse( @"<E2ETraceEvent xmlns=""http://schemas.microsoft.com/2004/06/E2ETraceEvent"">     <System xmlns=""http://schemas.microsoft.com/2004/06/windows/eventlog/system"">         <EventID>589828</EventID>         <Type>3</Type>         <SubType Name=""Information"">0</SubType>         <Level>8</Level>         <TimeCreated SystemTime=""2010-06-01T09:45:15.8102117Z"" />         <Source Name=""System.ServiceModel"" />         <Correlation ActivityID=""{00000000-0000-0000-0000-000000000000}"" />         <Execution ProcessName=""w3wp"" ProcessID=""5012"" ThreadID=""5"" />         <Channel />         <Computer>TESTSERVER3A</Computer>     </System>     <ApplicationData>         <TraceData>  <DataItem>      <TraceRecord xmlns=""http://schemas.microsoft.com/2004/10/E2ETraceEvent/TraceRecord"" Severity=""Information"">          <TraceIdentifier>http://msdn.microsoft.com/en-GB/library/System.ServiceModel.Activation.WebHostCompilation.aspx</TraceIdentifier>          <Description>Webhost compilation</Description>          <AppDomain>/LM/W3SVC/257188508/Root-1-129198591101343437</AppDomain>          <Source>System.ServiceModel.Activation.ServiceParser/39498779</Source>          <ExtendedData xmlns=""http://schemas.microsoft.com/2006/08/ServiceModel/StringTraceRecord"">   <VirtualPath>/Service.svc</VirtualPath>          </ExtendedData>      </TraceRecord>  </DataItem>         </TraceData>     </ApplicationData> </E2ETraceEvent>"); XNamespace nsSys = "http://schemas.microsoft.com/2004/06/windows/eventlog/system"; XElement xEl2 = xDoc.Element(nsSys + "System"); XElement xEl3 = xEl2.Element(nsSys + "Correlation"); XAttribute xAtt1 = xEl3.Attribute("ActivityID"); String sValue = xAtt1.Value; Console.WriteLine("sValue = {0}", sValue); Console.ReadKey();        }