Author: Marc D. Anderson
http://mdasblog.wordpress.com

<xsl:param>

A value you’ve passed into a template with <xsl:with-param>. You need to have an <xsl:param> at the top of the template for each value you expect to be passed into it.

I talked in the last post about passing values into templates using <xsl:with-param>. Whenever you pass these values, you need to tell the “receiving” template to expect them. You do this by using the <xsl:param> tag.

If we look at the example XSL again, we can see that there are <xsl:param> tags used in two places:

• At the top of the XSL, prior to any templates
• At the top of the dvt_1.body template

<XSL><xsl:stylesheet xmlns:x="<a href="http://www.w3.org/2001/XMLSchema">http://www.w3.org/2001/XMLSchema</a>" xmlns:d="<a href="http://schemas.microsoft.com/sharepoint/dsp">http://schemas.microsoft.com/sharepoint/dsp</a>" version="1.0" exclude-result-prefixes="xsl msxsl ddwrt" xmlns:ddwrt="<a href="http://schemas.microsoft.com/WebParts/v2/DataView/runtime">http://schemas.microsoft.com/WebParts/v2/DataView/runtime</a>" xmlns:asp="<a href="http://schemas.microsoft.com/ASPNET/20">http://schemas.microsoft.com/ASPNET/20</a>" xmlns:__designer="<a href="http://schemas.microsoft.com/WebParts/v2/DataView/designer">http://schemas.microsoft.com/WebParts/v2/DataView/designer</a>" xmlns:xsl="<a href="http://www.w3.org/1999/XSL/Transform">http://www.w3.org/1999/XSL/Transform</a>" xmlns:msxsl="urn:schemas-microsoft-com:xslt" xmlns:SharePoint="Microsoft.SharePoint.WebControls" xmlns:ddwrt2="urn:frontpage:internal">

  <xsl:output method="html" indent="no"/>
  <xsl:decimal-format NaN=""/>
  <xsl:param name="dvt_apos">'</xsl:param>
  <xsl:variable name="dvt_1_automode">0</xsl:variable>

  <xsl:template match="/">
    <xsl:call-template name="dvt_1"/>
  </xsl:template>

  <xsl:template name="dvt_1">
    <xsl:variable name="dvt_StyleName">Table</xsl:variable>
    <xsl:variable name="Rows" select="/dsQueryResponse/Rows/Row"/>
    <table border="0" width="100%" cellpadding="2" cellspacing="0">
      <tr valign="top">
        <xsl:if test="$dvt_1_automode = '1'" ddwrt:cf_ignore="1">
          <th width="1%" nowrap="nowrap"></th>
        </xsl:if>
        <th nowrap="nowrap">Title</th>
      </tr>
      <xsl:call-template name="dvt_1.body">
        <xsl:with-param name="Rows" select="$Rows"/>
      </xsl:call-template>
    </table>
  </xsl:template>

  <xsl:template name="dvt_1.body">
    <xsl:param name="Rows"/>
    <xsl:for-each select="$Rows">
      <xsl:call-template name="dvt_1.rowview"/>
    </xsl:for-each>
  </xsl:template>

  <xsl:template name="dvt_1.rowview">
    <tr>
      <xsl:if test="position() mod 2 = 1">
        <xsl:attribute name="class">ms-alternating</xsl:attribute>
      </xsl:if>
      <xsl:if test="$dvt_1_automode = '1'" ddwrt:cf_ignore="1">
        <td width="1%" nowrap="nowrap">
          <span ddwrt:amkeyfield="ID" ddwrt:amkeyvalue="ddwrt:EscapeDelims(string(@ID))" ddwrt:ammode="view"></span>
        </td>
      </xsl:if>
      <td>
        <xsl:value-of select="@Title"/>
      </td>
    </tr>
  </xsl:template>
</xsl:stylesheet></XSL>

At the top of the XSL, we see one use of <xsl:param>.  Anything which we declare at this level (outside any individual  templates) is available, or scoped, to the entire XSL section.

<xsl:param name="dvt_apos">'</xsl:param>

SharePoint Designer puts this silly little line of code in DVWPs to set up a parameter to represent the apostrophe character. Because of the highly reserved nature of this character, it can be a bear to work with, and this way you have a parameter containing it to use.

We need an <xsl:param> here for any values we’re declaring in the ParameterBindings section which we want to use in the XSL, too. So, for instance, if we declare the URL Server Variable in the ParameterBindings section: <ParameterBinding Name="URL" Location="ServerVariable(URL)" DefaultValue=""/>, then we need an <xsl:param> at the top of the XSL if we want to use the value: <xsl:param name="URL">.

In the dvt_1.body template, we can see:

<xsl:param name="Rows"/>

When the dvt_1.body template is called, Rows is being passed with <xsl:with-param>:

<xsl:call-template name="dvt_1.body">
  <xsl:with-param name="Rows" select="$Rows"/>
</xsl:call-template>

We need the <xsl:param> tag to “catch” the value that is being thrown in. This “catch” idea is required for anything that we pass into a template. Any parameter which we declare inside a template is available, or scoped, only within that template.

When you want to use a parameter which you’ve “caught”, you precede the name with a dollar sign. (The same is true for <xsl:variable>, but that’s the next installment.) So in the Rows example above, you’d use the parameter as $Rows (you’ll see this parameter a lot in the XSL). In the URL example, it’d be $URL.

Next up: <xsl:variable>

A value you create for use within a template which is only defined within the scope of that template.

Author: Marc D. Anderson
http://mdasblog.wordpress.com

Marc D. Anderson is a Co-Founder and the President of Sympraxis Consulting LLC, based in Newton, MA.  He has over 25 years of experience as a technology consultant and line manager across a wide spectrum of industries and organizational sizes.  Marc has done extensive consulting on knowledge management and collaboration and what makes them actually work in practice.  Marc is a very frequent “answerer” on the MSDN SharePoint – Design and Customization forum.