C# - 是否有可能(以及如何)使用SgmlReader执行XSL转换

Question

我需要使用XSLT转换HTML网页的内容 .因此我使用了SgmlReader并编写了下面显示的片段(我想,最后,它也是一个XmlReader ......)

XmlReader xslr = XmlReader.Create(new StringReader(
    "<?xml version=\"1.0\" encoding=\"UTF-8\"?>" +
    "<xsl:stylesheet xmlns:xsl=\"http://www.w3.org/1999/XSL/Transform\" version=\"1.0\">" +
    "<xsl:output method=\"xml\" encoding=\"UTF-8\" version=\"1.0\" />" +
    "<xsl:template match=\"/\">" +
    "<XXX xmlns:xsd=\"http://www.w3.org/2001/XMLSchema\"><xsl:value-of select=\"count(//br)\" /></XXX>" +
    "</xsl:template>" +
    "</xsl:stylesheet>"));

XslCompiledTransform xslt = new XslCompiledTransform();
xslt.Load(xslr);

using (SgmlReader html = new SgmlReader())
{
    StringBuilder sb = new StringBuilder();
    using (TextWriter sw = new StringWriter(sb))
    using (XmlWriter xw = new XmlTextWriter(sw))
    {
        html.InputStream = new StringReader(Resources.html_orig);
        html.DocType = "HTML";

        try
        {
            xslt.Transform(html, xw);
            string output = sb.ToString();
            System.Console.WriteLine(output);
        }
        catch (Exception exc)
        {
            System.Console.WriteLine("{0} : {1}", exc.GetType().Name, exc.Message);
            System.Console.WriteLine(exc.StackTrace);
        }
    }
}

尽管如此,我收到了错误消息

NullReferenceException : Object reference not set to an instance of an object.
   at MS.Internal.Xml.Cache.XPathDocumentBuilder.Initialize(XPathDocument doc, IXmlLineInfo lineInfo, String baseUri, LoadFlags flags)
   at MS.Internal.Xml.Cache.XPathDocumentBuilder..ctor(XPathDocument doc, IXmlLineInfo lineInfo, String baseUri, LoadFlags flags)
   at System.Xml.XPath.XPathDocument.LoadFromReader(XmlReader reader, XmlSpace space)
   at System.Xml.XPath.XPathDocument..ctor(XmlReader reader, XmlSpace space)
   at System.Xml.Xsl.Runtime.XmlQueryContext.ConstructDocument(Object dataSource, String uriRelative, Uri uriResolved)
   at System.Xml.Xsl.Runtime.XmlQueryContext..ctor(XmlQueryRuntime runtime, Object defaultDataSource, XmlResolver dataSources, XsltArgumentList argList, WhitespaceRuleLookup wsRules)
   at System.Xml.Xsl.Runtime.XmlQueryRuntime..ctor(XmlQueryStaticData data, Object defaultDataSource, XmlResolver dataSources, XsltArgumentList argList, XmlSequenceWriter seqWrt)
   at System.Xml.Xsl.XmlILCommand.Execute(Object defaultDocument, XmlResolver dataSources, XsltArgumentList argumentList, XmlSequenceWriter results)
   at System.Xml.Xsl.XmlILCommand.Execute(Object defaultDocument, XmlResolver dataSources, XsltArgumentList argumentList, XmlWriter writer, Boolean closeWriter)
   at System.Xml.Xsl.XmlILCommand.Execute(XmlReader contextDocument, XmlResolver dataSources, XsltArgumentList argumentList, XmlWriter results)
   at System.Xml.Xsl.XslCompiledTransform.Transform(XmlReader input, XmlWriter results)

我找到了一种解决方法,通过将HTML转换为XML然后应用转换,但这是一个低效的解决方案,因为:

1. 中间XHTML输出进入缓冲区,因此需要额外的内存
2. 转换过程需要额外的CPU处理,并且遍历相同的层次结构两次(理论上不必要).

所以(因为我知道StackOverflow社区总是提供很好的答案,而其他C#论坛让我完全失望; o)我会寻找反馈和建议,以便直接使用HTML执行XSL转换(即使SgmlReader需要被另一个替换)类似的图书馆).

谢谢你提前

Answer 1

您是否尝试过使用HTML Agility Pack而不是SgmlReader？您可以将 html 加载到其中，然后直接对其运行转换。不过，我不确定 XML 文档是否是内部创建的 - 尽管看起来好像不是，但您可能希望将内存和 CPU 使用情况与您尝试并放弃的转换方法进行比较。

//You already have your xslt loaded into var xslt...

HtmlDocument doc = new HtmlDocument();
doc.Load( ... );  //load your HTML doc, or use LoadXML from a string, etc  
xslt.Transform(doc, xw);

另请参阅这个问题：How to use HTML Agility pack