c# – 如何在XPathExpression实例中编程使用XPath函数？

我当前的程序需要使用编程方式创建一个XPathExpression实例来应用于XmlDocument. xpath需要使用一些XPath函数,如“ends-with”.但是,我找不到在XPath中使用“ends-with”的方法.一世

它会像下面那样抛出异常

Unhandled Exception:
System.Xml.XPath.XPathException:
Namespace Manager or XsltC ontext
needed. This query has a prefix,
variable,or user-defined function.
at
MS.Internal.Xml.XPath.CompiledXpathExpr.get_QueryTree()
at
System.Xml.XPath.XPathNavigator.Evaluate(XPathExpression
expr,XPathNodeIt erator context)
at
System.Xml.XPath.XPathNavigator.Evaluate(XPathExpression
expr)

代码如下：

XmlDocument xdoc = new XmlDocument();
    xdoc.LoadXml(@"<?xml version=""1.0"" encoding=""utf-8"" ?>
                        <myXml xmlns=""http://MyNamespace"" xmlns:fn=""http://www.w3.org/2005/xpath-functions""> 
                        <data>Hello World</data>
                    </myXml>");
    XPathNavigator navigator = xdoc.CreateNavigator();

    XPathExpression xpr;
    xpr = XPathExpression.Compile("fn:ends-with(/myXml/data,'World')");

    object result = navigator.Evaluate(xpr);
    Console.WriteLine(result);

在编译表达式时,我尝试更改代码以插入XmlNamespaceManager,如下所示

XmlDocument xdoc = new XmlDocument();
    xdoc.LoadXml(@"<?xml version=""1.0"" encoding=""utf-8"" ?>
                        <myXml xmlns=""http://MyNamespace"" xmlns:fn=""http://www.w3.org/2005/xpath-functions""> 
                        <data>Hello World</data>
                    </myXml>");
    XPathNavigator navigator = xdoc.CreateNavigator();
    XmlNamespaceManager nsmgr = new XmlNamespaceManager(xdoc.NaMetable);
    nsmgr.AddNamespace("fn","http://www.w3.org/2005/xpath-functions");

    XPathExpression xpr;
    xpr = XPathExpression.Compile("fn:ends-with(/myXml/data,'World')",nsmgr);

    object result = navigator.Evaluate(xpr);
    Console.WriteLine(result);

它在XPathExpression.Compile调用失败：

Unhandled Exception:
System.Xml.XPath.XPathException:
XsltContext is needed for this query
because of an unknown function. at
MS.Internal.Xml.XPath.CompiledXpathExpr.UndefinedXsltContext.ResolveFuncti
on(String prefix,String name,
XPathResultType[] ArgTypes) at
MS.Internal.Xml.XPath.FunctionQuery.SetXsltContext(XsltContext
context) at
MS.Internal.Xml.XPath.CompiledXpathExpr.SetContext(XmlNamespaceManager
nsM anager) at
System.Xml.XPath.XPathExpression.Compile(String
xpath,IXmlNamespaceResolv er
nsResolver)

任何人都知道用XPathExpression.Compile使用现成的XPath函数的技巧？
谢谢

解决方法

功能 ends-with()未为 XPath 1.0定义,但仅针对 XPath 2.0和 XQuery.

你在使用.NET. .NET在此日期不实现XPath 2.0,XSLT 2.0或XQuery.

可以轻松构建XPath 1.0表达式,其评估产生与函数ends-with()相同的结果：

$str2 = substring($str1,string-length($str1) – string-length($str2)1)

生成相同的布尔结果(true()或false())为：

($str1,$str2)

在具体情况下,您只需要替换$str1和$str2的正确表达式.相应地,它们是/ myXml / data和’World’.

所以,XPath 1.0表达式使用,相当于XPath 2.0表达式(/ myXml / data,’World’)是：

'World' = 
   substring(/myXml/data,string-length(/myXml/data) - string-length('World') +1
             )

原文链接：https://www.f2er.com/csharp/95946.html

c# – 如何在XPathExpression实例中编程使用XPath函数？

解决方法

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