A346 - XSL Templates

• Overview
• Templates

• Passing Parameters

• Receiving Parameters

• Debugging

Overview

Templates are modules of XSL instructions that are called from other templates. Templates promote modular designs and reuse in much the same way of functions. The following reviews templates and presents the use of template parameters to produce more general modules.

Templates

Templates are modules that can be applied or called.

apply

• <xsl:template match="Red"> defines a template that matches "Red" nodes of an XML or other node structure. 
• <xsl:apply-templates /> is used when templates are to be processed in the order of a node structure. The child nodes of the structure match the template name to determine which template is applied.
• <xsl:apply-templates select="name"/> is used when templates are to be applied a specific child node of a structure.
• <xsl:template match="/"> is the template matching the "/" or root and is processed first. It must call or apply other templates for those templates to be processed.

call

• <xsl:template name="validateForm"> defines a callable template named "validateForm".
• <xsl:param name="theForm"/> defines a template parameter.
• <xsl:call-templates select="validateForm"/> is used when templates are to be processed in an arbitrary order.
• <xsl:with-param name="theForm" select=" 'document.LoginForm' " /> specifies that the template parameter named theForm value is the text 'document.LoginForm'.

The example shows the XSL at left, the resulting HTML in the middle and the rendering at right.

RowColumn.htm

<xsl:stylesheet version="2.0" 
   xmlns:xsl="http://www.w3.org/1999/XSL/Transform" 
   xmlns="http://www.w3.org/1999/xhtml">

   <xsl:template match="/">
      <table border="1">
        <xsl:call-template name="RowColumn"/>
        <xsl:call-template name="RowColumn"/>
        <xsl:call-template name="RowColumn"/>
      </table>
   </xsl:template>

   <xsl:template name="RowColumn">
          <tr><td>Row</td></tr>
   </xsl:template>
</xsl:stylesheet> 

HTML produced

<?xml version="1.0" encoding="UTF-16" ?>
<table border="1">
	<tr><td>Row</td></tr>
	<tr><td>Row</td></tr>
	<tr><td>Row</td></tr>
</table>

RowColumn.xml

<?xml-stylesheet type="text/xsl" 
               href="RowColumn.htm"?>
<top>
</top>

Passing Parameters

Template parameters are text passed from the calling template to the called template.  Passing 'Second' as the value of the Row parameter to template RowColumn:

<xsl:call-template name="RowColumn">
             <xsl:with-param name="Row" select=" 'Second' " />
</xsl:call-template>

• Numbers - Numbers can be passed without quotes. For example: <xsl:with-param name="Row" select="3" />
• Strings - Must be quoted, for example: <xsl:with-param name="Row" select=" 'First' " />

Receiving Parameters

Receiving 'Second' from the above example to Row parameter:

   <xsl:template name="RowColumn">
         <xsl:param name="Row" />
            <tr><td>
                  <xsl:value-of select="$Row" />
           </td></tr>
   </xsl:template>

The value of the parameter is available by 2 different methods dependent upon where used. For the Row parameter:

1. HTML
   • {$Row} is the value of $Row parameter when an attribute inside an HTML tag, for example: <span id="{$Row}" />
   • <xsl:value-of select="$Row" /> is the value of the $Row parameter when outside an HTML tag.
2. JavaScript - <xsl:value-of select="$Row" />

If one doesn't work, try the other.

In the following example, the text 'First', 'Second', and 'Third' is passed through the parameter to template RowColumn named Row.

<xsl:stylesheet version="2.0" 
   xmlns:xsl="http://www.w3.org/1999/XSL/Transform" 
   xmlns="http://www.w3.org/1999/xhtml">

   <xsl:template match="/">
      <table border="1">
         <xsl:call-template name="RowColumn">
             <xsl:with-param name="Row" select=" 'First' " />
         </xsl:call-template>
         <xsl:call-template name="RowColumn">
             <xsl:with-param name="Row" select=" 'Second' " />
         </xsl:call-template>
         <xsl:call-template name="RowColumn">
             <xsl:with-param name="Row" select="3" />
         </xsl:call-template>
       </table>
   </xsl:template>

   <xsl:template name="RowColumn">
         <xsl:param name="Row" />
         <tr>
            <td id="{$Row}">
                  <xsl:value-of select="$Row" />
            </td>
         </tr>
   </xsl:template>
</xsl:stylesheet>

<?xml version="1.0" encoding="UTF-16" ?>
<table border="1">
	<tr>
	        <td id="First">First</td>
	</tr>
	<tr>
	        <td id="Second">Second</td>
	</tr>
	<tr>
	        <td id="3">3</td>
	</tr>
</table>

Debugging

We need to see the HTML produced by the style sheet for debugging. The browser source view only displays the XML file, not useful when debugging style sheets.

• msxsl - Applies the style sheet to XML and displays HTML and useful error messages.