c# - XPath 扩展方法在 .NET 3.5 中失败，在 .NET 4.0 中有效

Question

我创建了一个标准的 XsltContext 类并按如下方式调用它:

        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);

在 .net 4.0 下运行时它工作正常。但是在 .NET 3.5(我们目前必须使用)下，我得到:

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: 

知道为什么吗？

示例代码位于 http://www.windwardreports.com/temp/CustomXPathFunctionsBug.zip

谢谢 - 戴夫

Answer 1

想出了一个办法来做到这一点。使用像这样的 XPathExpression:

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

至于为什么 - 我的猜测是 Evaluate(string, context) 仅在 .NET 3.5 中将它用于 namespace ，而 XPathExpression 将它用于所有内容。不过，关键是这行得通。

ps - 请对这个答案中的鼻涕点赞 - 这真的很难弄清楚。