Using XSLT to generate a multi-level tree menu from XML

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Introduction

This article will demonstrate a simple and generic way to use XSLT to generate a multi-level HTML tree menu from an XML source. JScript is used for expanding and contracting the menu entries. (This requires a minimum of Internet Explorer 5. I have not tested this on any other browsers.)

The XML Source

This is a subset of the source XML (full XML source is in the zip file).

<menu>
 <entry>
  <text>In-House</text>
  <url>InHouse.htm</url>
  <entry>
   <text>Web Development</text>
   <url>WebDev.htm</url>
  </entry>
 </entry>
</menu>

The XSLT

For each menu entry, the XSLT processes it, then drills down until it has processed that entry's last child.

<?xml version="1.0" ?>
<xsl:stylesheet version="1.0" 
  xmlns:xsl="http://www.w3.org/1999/XSL/Transform">

<xsl:template match="/">
 <xsl:for-each select="//menu/entry">
  <xsl:call-template name="SubMenu">
   <xsl:with-param name="strCSS">Parent IsVisible</xsl:with-param>
  </xsl:call-template>
 </xsl:for-each>
</xsl:template>

<xsl:template name="SubMenu">
 <xsl:param name="strCSS" />
 
 <xsl:variable name="strURL" select="url" />
 
 <div class="{$strCSS}">
  <xsl:choose>
   <xsl:when test="count(entry) > 0">
    <!-- Element has children, it can be expanded -->
    <input type="hidden" id="hidIsExpanded" value="0" />
    <label id="lblExpand" class="Expander" onclick="ExpanderClicked()">+
    </label>
   </xsl:when>
   <xsl:otherwise>
    <label class="Expander">  </label>
   </xsl:otherwise>
  </xsl:choose>
  
  <a href="{$strURL}"><xsl:value-of select="text" /></a>
  <xsl:for-each select="entry">
   <xsl:call-template name="SubMenu">
    <xsl:with-param name="strCSS">NotVisible</xsl:with-param>
   </xsl:call-template>
  </xsl:for-each>
 </div>
</xsl:template>

</xsl:stylesheet>

Transforming the XML on the server

ASP is used to perform server-side transformation of the XML.

<%
   dim xmlMenu
   dim xslMenu
   
   'Get the source XML
   set xmlMenu = server.CreateObject("Microsoft.XMLDOM")
   xmlMenu.async = false
   xmlMenu.load server.MapPath("TreeFromXMLUsingXSLT.xml")
   
   'Get the XSLT to transform the XML
   set xslMenu = server.CreateObject("Microsoft.XMLDOM")
   xslMenu.async = false
   xslMenu.load server.MapPath("TreeFromXMLUsingXSLT.xsl")
   
   'Transform the source XML using XSLT
   Response.Write xmlMenu.transformNode(xslMenu)
   
   set xmlMenu = nothing
   set xslMenu = nothing
%>

Controlling the menu entries

Client-side JScript is used to first determine whether a menu entry has been expanded or collapsed, and then adjusts the selected menu entry's style settings.

<script language="jscript">
function ExpanderClicked()
{
    //Get the element that was clicked
    var ctlExpander = event.srcElement;
    var ctlSelectedEntry = ctlExpander.parentElement;
    //Get all the DIV elements that are direct descendants
    var colChild = ctlSelectedEntry.children.tags("DIV");
    if(colChild.length > 0)
    {
        var strCSS;
        //Get the hidden element that 
        //indicates whether or not entry is expanded
        var ctlHidden = ctlSelectedEntry.all("hidIsExpanded");
      
        if(ctlHidden.value == "1")
        {
            //Entry was expanded and is being contracted
            ctlExpander.innerHTML = "+ ";
            ctlHidden.value = "0";
            strCSS = "NotVisible";
        }
        else
        {
            //Entry is being expanded
            ctlExpander.innerHTML = "- ";
            ctlHidden.value = "1";
            strCSS = "IsVisible";
        }
        //Show all the DIV elements that are direct children
        for(var intCounter = 0; intCounter < colChild.length; intCounter++)
        {
            colChild[intCounter].className = strCSS;
        }
    }
}
</script>

Style setting

CSS settings are used to specify if a menu entry should be visible or hidden. The IsVisible class sets the element to be displayed, as a block element. The NotVisible class sets the element to be hidden.

body
{
   font-family: Verdana;
   font-size: x-small;
}
.IsVisible
{
   display: block;
}
.NotVisible
{
   display: none;
}
.Expander
{
   cursor: hand;
   font-family: Courier;
}
.Parent DIV
{
   margin-Left: 15px !important;
}

The last setting (.Parent DIV) indicates that only the elements below the one with the "Parent" class, will have a margin. This is to prevent the root menu entries from also having a margin.

Using images instead of + and -

It is fairly simple to show images instead of a "+" and "-" next to each entry. To do this, alter the XSLT and replace the <label> element that is next to the link, with an <img> element. In the JScript, instead of setting the InnerHTML property of the ctlExpander variable, set the src attribute to show a different image. Here is an example: