XML/ XSL Transformation issue in C# routine to output HTML with embedded CSS content

Question

I have a XSL script that has this towards the top:

<head>
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta content="text/html; charset=utf-8" http-equiv="Content-Type" />
    <xsl:choose>
        <xsl:when test="$CSSFile1 !=''">
            <style type="text/css">
                <xsl:value-of select="$CSSFile1"/>
            </style>
        </xsl:when>
        <xsl:otherwise>
            <link rel="stylesheet" type="text/css" href="Workbook-S-140-PublicTalk-WatchtowerStudy-ServiceTalk-Videoconference2.css"/>
            <link rel="stylesheet" type="text/css" href="Workbook-S-140-PublicTalk-WatchtowerStudy-ServiceTalk-Zoom.css"/>
        </xsl:otherwise>
    </xsl:choose>
    <title>
        <xsl:value-of select="//Labels/Congregation"/>&#160;<xsl:value-of select="//Labels/Title" />
    </title>
</head>

As you can see, when $CSSFile1 is empty it should include two style sheets.

The above is part of a XSL / XML transformation that is used in a CHtmlView control in my MFC project and in itself it works fine.

But ...

I have a feature that allows the user to export the same data to a HTML file and it is support to do this using a C# DLL that I wrote which does it's own transformation using the same data. The code:

public bool TransformXMLToHTML(string strTransformXSLPath, string strScheduleXMLPath, string strScheduleHTMLPath)
{
    try
    {
        var xmlResolver = new XmlUrlResolver();
        XsltArgumentList argsList = new XsltArgumentList();

        string strRootPath = Path.GetDirectoryName(strTransformXSLPath);

        // Read the XSL file and locate all the CSS documents that are used
        int iFileCount = 0;
        string[] lines = File.ReadAllLines(strTransformXSLPath);
        foreach (string line in lines)
        {
            if ((line).Trim().Contains("text/css"))
            {
                int iHREFIndex = line.IndexOf("href=\"");
                if (iHREFIndex != -1)
                {
                    string strCSSFile = line.Substring(iHREFIndex + 6);

                    int iQuoteIndex = strCSSFile.IndexOf("\"");
                    if (iQuoteIndex != -1)
                    {
                        strCSSFile = strCSSFile.Substring(0, iQuoteIndex);

                        // Build full path and make sure the file exists
                        string strCSSFilePath = Path.Combine(strRootPath, strCSSFile);
                        if(File.Exists(strCSSFilePath))
                        {
                            // Establish the parameter name
                            iFileCount++;
                            string strParamName = "CSSFile" + iFileCount.ToString();

                            // Read the content and attach
                            string strCSSFileContent = File.ReadAllText(strCSSFilePath);
                            argsList.AddParam(strParamName, "", strCSSFileContent);
                        }
                    }
                }
            }
        }

        // Now perform the transformation
        XslCompiledTransform transformer = new XslCompiledTransform();
        transformer.Load(strTransformXSLPath, new XsltSettings { EnableDocumentFunction = true }, xmlResolver);

        using (StreamWriter sw = new StreamWriter(strScheduleHTMLPath))
        {
            transformer.Transform(strScheduleXMLPath, argsList, sw);
        }
    }
    catch (Exception ex)
    {
        SimpleLog.Log(ex);
        return false;
    }

    return true;
}

Something is going wrong because the transformation is supposed to embed both CSS files and it only ends up embedded the first one. There are no errors raised.

Have you considered using XPath to identitfy the `link[@rel = 'stylesheet'][@type = 'text/css']` elements in the XSLT loaded as an XPathDocument or XmlDocument instead of parsing it as plain text? Perhaps that makes it easier reading out the `href` attribute values and then ckecking for the files. — Martin Honnen, Jan 17 '21 at 17:10

score 2 · Accepted Answer · edited Jan 17 '21 at 18:14

First, I agree w/Martin re: XPath. Hand parsing XML / XSL is a red flag for me. Use all the tools available to you in XML / XSL and XPath. Have a look at XmlDocument.SelectNodes for looking up nodes and doing quick DOM manipulation. I know it's "out of the way", but a few minutes mastering XPath and DOM manipulation will pay dividends for a long time to come.

RE: Your issue

"the transformation is supposed to embed both CSS files and it only ends up embedded the first one."

When $CSSFile1 is present, the XSL only outputs $CSSFile1. However the second file content is output as a second parameter $CSSFile2 (that you're not outputting). You can resolve in two ways.

Append content from CSSFile2 into your strCSSFileContent variable. Then "everything" will be contained in $CSSFile1

or alternatively -

In your XSL output both CSSFile1 AND CSSFile2

Good luck, hope this is helpful to you.

Thanks for your answer. I will certain look at using the alternative methodology. And based on your answer I was able to adjust my XSL logic as needed. Much appreciated. — Andrew Truckle, Jan 17 '21 at 18:16

XML/ XSL Transformation issue in C# routine to output HTML with embedded CSS content

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