HtmlAgilityPack XPath大小写忽略 [英] HtmlAgilityPack XPath case ignoring
问题描述
当我使用
SelectSingleNode("//meta[@name='keywords']")
它不起作用，但是当我使用原始文档中使用的相同大小写时，效果很好：
it doesn't work, but when I use the same case that used in original document it works good:
SelectSingleNode("//meta[@name='Keywords']")
所以问题是如何设置忽略大小写？
So the question is how can I set case ignoring?
推荐答案
<如果需要更全面的解决方案，则可以为XPath处理器编写扩展功能，该功能将执行不区分大小写的比较。这是很多代码，但是您只编写了一次。
If you need a more comprehensive solution, you can write an extension function for the XPath processor which will perform a case insensitive comparison. It is quite a bit of code, but you only write it once.
实现扩展后，您可以按以下方式编写查询
After implementing the extension you can write your query as follows
"//meta[@name[Extensions:CaseInsensitiveComparison('Keywords')]]"
其中 Extensions：CaseInsensitiveComparison 是以下示例中实现的扩展功能。
Where Extensions:CaseInsensitiveComparison is the extension function implemented in the sample below.
注意：：此测试没有经过很好的测试，我只是为了响应而将其放在一起，所以不存在错误处理等！
NOTE: this is not well tested I just threw it together for this response so the error handling etc. is non-existent!
以下是自定义XSLT上下文的代码，该代码提供一个或多个扩展功能
The following is the code for the custom XSLT Context which provides one or more extension functions
using System;
using System.Xml.XPath;
using System.Xml.Xsl;
using System.Xml;
using HtmlAgilityPack;
public class XsltCustomContext : XsltContext
{
public const string NamespaceUri = "http://XsltCustomContext";
public XsltCustomContext()
{
}
public XsltCustomContext(NameTable nt)
: base(nt)
{
}
public override IXsltContextFunction ResolveFunction(string prefix, string name, XPathResultType[] ArgTypes)
{
// Check that the function prefix is for the correct namespace
if (this.LookupNamespace(prefix) == NamespaceUri)
{
// Lookup the function and return the appropriate IXsltContextFunction implementation
switch (name)
{
case "CaseInsensitiveComparison":
return CaseInsensitiveComparison.Instance;
}
}
return null;
}
public override IXsltContextVariable ResolveVariable(string prefix, string name)
{
return null;
}
public override int CompareDocument(string baseUri, string nextbaseUri)
{
return 0;
}
public override bool PreserveWhitespace(XPathNavigator node)
{
return false;
}
public override bool Whitespace
{
get { return true; }
}
// Class implementing the XSLT Function for Case Insensitive Comparison
class CaseInsensitiveComparison : IXsltContextFunction
{
private static XPathResultType[] _argTypes = new XPathResultType[] { XPathResultType.String };
private static CaseInsensitiveComparison _instance = new CaseInsensitiveComparison();
public static CaseInsensitiveComparison Instance
{
get { return _instance; }
}
#region IXsltContextFunction Members
public XPathResultType[] ArgTypes
{
get { return _argTypes; }
}
public int Maxargs
{
get { return 1; }
}
public int Minargs
{
get { return 1; }
}
public XPathResultType ReturnType
{
get { return XPathResultType.Boolean; }
}
public object Invoke(XsltContext xsltContext, object[] args, XPathNavigator navigator)
{
// Perform the function of comparing the current element to the string argument
// NOTE: You should add some error checking here.
string text = args[0] as string;
return string.Equals(navigator.Value, text, StringComparison.InvariantCultureIgnoreCase);
}
#endregion
}
}
然后，您可以在XPath查询中使用上述扩展功能，这是我们案例的示例
You can then use the above extension function in your XPath queries, here is an example for our case
class Program
{
static string html = "<html><meta name=\"keywords\" content=\"HTML, CSS, XML\" /></html>";
static void Main(string[] args)
{
HtmlDocument doc = new HtmlDocument();
doc.LoadHtml(html);
XPathNavigator nav = doc.CreateNavigator();
// Create the custom context and add the namespace to the context
XsltCustomContext ctx = new XsltCustomContext(new NameTable());
ctx.AddNamespace("Extensions", XsltCustomContext.NamespaceUri);
// Build the XPath query using the new function
XPathExpression xpath =
XPathExpression.Compile("//meta[@name[Extensions:CaseInsensitiveComparison('Keywords')]]");
// Set the context for the XPath expression to the custom context containing the
// extensions
xpath.SetContext(ctx);
var element = nav.SelectSingleNode(xpath);
// Now we have the element
}
}
这篇关于HtmlAgilityPack XPath大小写忽略的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
