使用ms:XPathExpression中的xpath函数 [英] Using ms: xpath functions inside XPathExpression

问题描述

我正在尝试使用Microsoft XPath扩展功能(例如ms:string-compare

I am trying to use Microsoft XPath Extension Functions (such as ms:string-compare http://msdn.microsoft.com/en-us/library/ms256114.aspx) inside an XPathExpression object.

这些函数是MSXML库内部的扩展，如果我在XslCompiledTransform中使用它们(简单地添加"ms"命名空间)，它们的工作就像一个魅力:

These functions are extensions inside the MSXML library, and if I use them in an XslCompiledTransform (simply adding the "ms" namespace) they work like a charm:

var xsl =
    @"
<?xml version=""1.0"" encoding=""UTF-8""?>
<xsl:stylesheet version=""2.0"" xmlns:xsl=""http://www.w3.org/1999/XSL/Transform"" 
        xmlns:xs=""http://www.w3.org/2001/XMLSchema"" 
        xmlns:fn=""http://www.w3.org/2005/xpath-functions"" 
        xmlns:ms=""urn:schemas-microsoft-com:xslt"">
 <xsl:output method=""xml"" version=""1.0"" encoding=""UTF-8"" indent=""yes""/>
 <xsl:template match=""/Data"">
  <xsl:element name=""Result"">
   <xsl:value-of select=""ms:string-compare(@timeout1, @timeout2)""/>
  </xsl:element>
 </xsl:template>
</xsl:stylesheet>";

var xslDocument = new XmlDocument();
xslDocument.LoadXml(xsl);

var transform = new XslCompiledTransform();
transform.Load(xslDocument);

然后我尝试在XPathExpression中使用它们:

Then I tried using them in an XPathExpression:

XPathNavigator nav = document.DocumentElement.CreateNavigator();
XPathExpression expr = nav.Compile("ms:string-compare(/Data/@timeout1, /Data/@timeout2)");

XmlNamespaceManager manager = new XmlNamespaceManager(document.NameTable);
manager.AddNamespace("ms", "urn:schemas-microsoft-com:xslt");
expr.SetContext(manager);

nav.Evaluate(expr);

但是我得到一个异常由于功能未知，此查询需要XsltContext".

But I get an exception "XsltContext is needed for this query because of an unknown function".

XsltContext是特定的XmlNamespaceManager，但我不知道是否可以在没有实际XslCompiledTransform(它是抽象的)的情况下实例化它并将其用作我的表达上下文.

XsltContext is a specific XmlNamespaceManager, but I don't know if it's possible to instantiate it without an actual XslCompiledTransform (it's abstract) and use it as my expression context.

是否有任何方法(或使用XPathExpression内部使用ms:扩展的其他方法)?

Is there any way to do this (or any other way to use ms: extensions inside an XPathExpression)?

推荐答案

.net框架dom类中不包含这些ms前缀的函数.您需要创建自定义函数才能执行相同的操作.

These ms prefixed functions are not included in .net framework dom classes. you need to create your custom functions to do same thing.

您可以在下面使用示例代码；

you may use sample code below;

string xpath = "my:string-compare('1','1)";

System.Xml.XmlNamespaceManager nsManager = new XsltContext();

nav.Select(xpath, nsManager );

或

XPathExpression compiledXPath = XPathExpression.Compile(xpath);

compiledXPath.SetContext(nsManager);

nav.Evaluate(compiledXPath);

您将需要这些课程；

public class XsltContext : System.Xml.Xsl.XsltContext
{
    public XsltContext()
    {
        Initialize();
    }

    public XsltContext(System.Xml.NameTable nameTable)
        : base(nameTable)
    {
        Initialize();
    }

    private void Initialize()
    {
        RegisterFunction("my", "string-compare", typeof(StringCompare));
    }

    public override string LookupNamespace(string prefix)
    {
        return base.LookupNamespace(prefix);
    }

    public override int CompareDocument(string baseUri, string nextbaseUri)
    {
        return string.CompareOrdinal(baseUri, nextbaseUri);
    }

    public override bool PreserveWhitespace(System.Xml.XPath.XPathNavigator node)
    {
        return false;
    }

    public void RegisterFunction(string prefix, string name, Type function)
    {
        if (function == null)
            throw new ArgumentNullException("function");

        if (name == null)
            throw new ArgumentNullException("name");

        functions[prefix + ":" + name] = function;
    }

    Dictionary<string, Type> functions = new Dictionary<string, Type>();

    public override System.Xml.Xsl.IXsltContextFunction ResolveFunction(string prefix, string name, System.Xml.XPath.XPathResultType[] argTypes)
    {
        Type functionType = null;

        if (functions.TryGetValue(prefix + ":" + name, out functionType))
        {
            System.Xml.Xsl.IXsltContextFunction function = Activator.CreateInstance(functionType) as System.Xml.Xsl.IXsltContextFunction;

            return function;
        }

        return null;
    }

    public override System.Xml.Xsl.IXsltContextVariable ResolveVariable(string prefix, string name)
    {
        return null;
    }

    public override bool Whitespace
    {
        get
        {
            return false;
        }
    }

    internal static string GetValue(object v)
    {
        if (v == null)
            return null;

        if (v is System.Xml.XPath.XPathNodeIterator)
        {
            foreach (System.Xml.XPath.XPathNavigator n in v as System.Xml.XPath.XPathNodeIterator)
                return n.Value;
        }

        return Convert.ToString(v);
    }

}

class StringCompare : System.Xml.Xsl.IXsltContextFunction
{
    public System.Xml.XPath.XPathResultType[] ArgTypes
    {
        get
        {
            return new System.Xml.XPath.XPathResultType[]
            {
                System.Xml.XPath.XPathResultType.String,
                System.Xml.XPath.XPathResultType.String,
                System.Xml.XPath.XPathResultType.String
            };
        }
    }

    public object Invoke(System.Xml.Xsl.XsltContext xsltContext, object[] args, System.Xml.XPath.XPathNavigator docContext)
    {
        string arg1 = XsltContext.GetValue(args[0]);
        string arg2 = XsltContext.GetValue(args[1]);

        string locale = "en-US";

        if (args.Length > 2)
            locale = XsltContext.GetValue(args[2]);

        System.Globalization.CultureInfo culture = System.Globalization.CultureInfo.GetCultureInfo(locale);

        return string.Compare(arg1, arg2, false, culture);
    }

    public int Maxargs
    {
        get
        {
            return 3;
        }
    }

    public int Minargs
    {
        get 
        {
            return 2;
        }
    }

    public System.Xml.XPath.XPathResultType ReturnType
    {
        get
        {
            return System.Xml.XPath.XPathResultType.Number;
        }
    }
}

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