Xml Xslt Xslt 1.0

How to Add an Image in XML to HTML Transformation using `XSLT`

Transforming XML documents into HTML can sometimes be tricky, especially when dealing with elements like images. Many developers encounter errors when trying to implement this, and understanding the root cause can help in implementing an effective solution. In this post, we’ll break down a common problem and present a simple and efficient way to add images in your XML to HTML transformations.

The Problem

Consider a simple XML document that contains image information. If you’re attempting to transform it into HTML and run into the error message:

“Cannot write an attribute node when no element start tag is open,”

This indicates that there is a problem with how you are trying to add the image tag’s attributes using XSLT. Let’s take a look at the XML content and the XSLT code that may lead to this issue.

Example XML Content

<root>
    <HeaderText>
        <HeaderText>Dan Testing</HeaderText>
    </HeaderText>
    <Image>
        <img width="100" height="100" alt="FPO lady" src="/uploadedImages/temp_photo_small.jpg"/>
    </Image>
    <BodyText>
        <p>This is a test of the body text<br /></p>
    </BodyText>
    <ShowLinkArrow>false</ShowLinkArrow>
</root>

Corresponding XSLT Code

<xsl:stylesheet version="1.0" extension-element-prefixes="msxsl"
    exclude-result-prefixes="msxsl js dl" xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
    xmlns:js="urn:custom-javascript" xmlns:msxsl="urn:schemas-microsoft-com:xslt"
    xmlns:dl="urn:datalist">
    <xsl:output method="xml" version="1.0" omit-xml-declaration="yes" indent="yes" encoding="utf-8"/>
    <xsl:template match="/" xml:space="preserve">
        <img>
            <xsl:attribute name="width">
                100
            </xsl:attribute>
            <xsl:attribute name="height">
                100
            </xsl:attribute>
            <xsl:attribute name="class">
                CalloutRightPhoto
            </xsl:attribute>
            <xsl:attribute name="src">
                <xsl:copy-of select="/root/Image/node()"/>
            </xsl:attribute>
        </img>
    </xsl:template>
</xsl:stylesheet>

Here, the issue lies in the following code snippet:

<xsl:attribute name="src">
    <xsl:copy-of select="/root/Image/node()"/>
</xsl:attribute>

The xsl:copy-of instruction attempts to copy a node or nodeset, but attributes can only contain textual values not entire nodes.

The Solution

Instead, you can use the xsl:value-of instruction or an Attribute Value Template (AVT) to achieve the desired output more effectively.

Recommended Approach: Using an Attribute Value Template

A much shorter and elegant solution is as follows:

<img width="100" height="100" src="{/root/Image/node()}" class="CalloutRightPhoto"/>

What are Attribute Value Templates (AVT)?

The use of {} in the attribute signifies an Attribute Value Template.
It allows you to incorporate XPATH expressions that return a textual value, making it ideal for setting attributes dynamically.

Why This Works

This single line replaces the need for multiple xsl:attribute lines, reducing complexity.
The XPath expression informs the XSLT processor to take the textual value when used within the AVT.

Conclusion

Adding an image when transforming an XML document to HTML via XSLT doesn’t have to be complicated. By employing Attribute Value Templates, you can effectively streamline your code while avoiding common errors. Next time you encounter issues with XSLT image incorporation, remember to leverage the power of AVTs for a clean and efficient solution.

Following these principles will make handling XSLT transformations smoother and help produce the results you want without unnecessary errors. Happy coding!

How to Add an Image in XML to HTML Transformation using XSLT