How can I correctly extract the GUID from the 'ActivityID' attribute in an XML document with namespaces using LINQ to XML?

LINQ to XML with Namespaces in XDocuments

Querying XML with namespaces in XDocuments can be challenging. Consider the following XML:

<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>

The following code will not extract the GUID from the "ActivityID" attribute:

XDocument xDoc = XDocument.Parse(CurrentString);
XElement xEl1 = xDoc.Element("E2ETraceEvent");
XElement xEl2 = xEl1.Element("System");
XElement xEl3 = xEl2.Element("Correlation");
XAttribute xAtt1 = xEl3.Attribute("ActivityID");
String sValue = xAtt1.Value;

Solution:

To work with namespaces, use the following code:

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;

Complete Source for Trial:

        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();
        }

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