Question

I created a standard XsltContext class and call it as follows:

        XPathCustomContext context = new XPathCustomContext(new NameTable());
        context.AddNamespace("windward", XPathCustomContext.Namespace);
        XsltArgumentList varList = new XsltArgumentList();
        varList.AddParam("stat-index", "", 0);
        context.ArgList = varList;

        XmlDocument doc = new XmlDocument();
        doc.Load("c:\\test\\order.xml");
        object xx = doc.CreateNavigator().Evaluate("/order[1]/customer[1]/num[@negone = $stat-index]", context);

When running under .net 4.0 it works fine. But under .NET 3.5 (which we have to use at present) I get:

System.Xml.XPath.XPathException was unhandled
  Message=XsltContext is needed for this query because of an unknown function.
  Source=System.Xml
  StackTrace:
       at MS.Internal.Xml.XPath.CompiledXpathExpr.UndefinedXsltContext.ResolveVariable(String prefix, String name)
       at MS.Internal.Xml.XPath.VariableQuery.SetXsltContext(XsltContext context)
       at MS.Internal.Xml.XPath.LogicalExpr.SetXsltContext(XsltContext context)
       at MS.Internal.Xml.XPath.FilterQuery.SetXsltContext(XsltContext input)
       at MS.Internal.Xml.XPath.CompiledXpathExpr.SetContext(XmlNamespaceManager nsManager)
       at System.Xml.XPath.XPathExpression.Compile(String xpath, IXmlNamespaceResolver nsResolver)
       at System.Xml.XPath.XPathNavigator.Evaluate(String xpath, IXmlNamespaceResolver resolver)
       at CustomXpathFunctions.Program.Main(String[] args) in c:\src\CustomXpathFunctions\Program.cs:line 62
       at System.AppDomain._nExecuteAssembly(Assembly assembly, String[] args)
       at System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args)
       at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
       at System.Threading.ThreadHelper.ThreadStart_Context(Object state)
       at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
       at System.Threading.ThreadHelper.ThreadStart()
  InnerException: 

Any idea why?

Sample code at http://www.windwardreports.com/temp/CustomXPathFunctionsBug.zip

thanks – dave

Answer 1

Figured out a way to do this. Use an XPathExpression like:

XPathNavigator nav = doc.CreateNavigator();
XPathExpression exp = nav.Compile("/order[1]/customer[1]/num[@negone = $stat]");
exp.SetContext(ctx);
object zzz = nav.Evaluate(exp);

As to why – my guess is Evaluate(string, context) uses it for namespaces only in .NET 3.5 while XPathExpression uses it for everything. The critical point though is this works.

ps – Please upvote the snot out of this answer – this was really hard to figure out.