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XML / XSL Transformation in an ASP.NET Page

If in previous posts I was presenting the greatness of Java when perform XML - XSL transformations, I am attempting now to do the same thing only in ASP.NET and C#.

The ASP.NET control that applies XSL templates to XML is called Xml (or <asp:Xml>). In its standard use case, it is very simple to use:
  • specify a DocumentSource attribute pointing to the server location of your XML file;
  • specify a TransformSource attribute indicating the location of the XSL file;
    <asp:Xml DocumentSource="~/navigation.xml" TransformSource="~/breadcrumb.xsl" runat="server" />

The problems however quickly arise -- for example when I use the XML generated by my Navigation TBB, I got error "'tcm' is an undeclared prefix. Line 1, position 2.". Obviously, I needed to add the namespace declaration for tcm. My new XML looks like this now:

<tcm:ListItems ID="tcm:1-1-4" Title="Root" xmlns:tcm="http://www.tridion.com/ContentManager/5.0">
  <tcm:Item ID="tcm:1-2-4" Title="010 About Us" DisplayTitle="About Us" Url="/about-us">
    <tcm:Item ID="tcm:1-3-64" Title="010 Who are we?" DisplayTitle="Who are we?" Url="/about-us/who-are-we.html"/>
  </tcm:Item>
  <tcm:Item ID="tcm:1-4-64" Title="020 Contact Us" DisplayTitle="Contact Us" Url="/contact-us.html"/>
</tcm:ListItems>

Furthermore, the Breadcrumb XSL I used was not supported by ASP.NET. Apparently template selector cannot have variable parts in it... that's only possible for XSLT 2.0. ASP.NET does not have XSLT 2.0 capabilities (out of the box). One would get error "'tcm:Item[@ID=$PageUri]' is an invalid key pattern. It either contains a variable reference or 'key()' function". God, I miss Java :)

So I had to rewrite the following template:

  <xsl:template match="tcm:Item[@ID=$PageUri]">
    <xsl:call-template name="breadcrumb-item">
      <xsl:with-param name="current-node" select=".."/>
    </xsl:call-template>
    <b><xsl:value-of select="@DisplayTitle"/></b>
    <xsl:apply-templates/>
  </xsl:template>

into the sub-optimal following construct:

  <xsl:template match="tcm:Item">
    <xsl:if test="@ID=$PageUri">
      <xsl:call-template name="breadcrumb-item">
        <xsl:with-param name="current-node" select=".."/>
      </xsl:call-template>
      <b><xsl:value-of select="@DisplayTitle"/></b>
    </xsl:if>
    <xsl:apply-templates/>
  </xsl:template>

Lastly, the major issue was with passing parameters into the transformation. I need to pass a parameter PageUri to be available inside the XSL at transform time. The Xml control does not provide for a simple markup notation to pass-in parameters (not like Java does). Instead, it provides property TransformArgumentList, where the developer needs to add the parameters in some code-behind fashion. Ugly!

The code is rather simple:

    XsltArgumentList xslArg = new XsltArgumentList();
    xslArg.AddParam("PageUri", "", pageUri);
    control.TransformArgumentList = xslArg;

But how do I get this code executed in code-behind? And how to pass the pageUri from the ASPX page into the code-behind? All examples I found were telling me to use the Page_Init method. This didn't work for me, since I needed to read a pageUri value that was written into the ASPX page.

Finally, I decided to use the OnLoad event for the Xml control and an inline Page_Init on the ASPX page. Ugly!

So the ASPX markup looks like this:

<script runat="server">
   protected void Page_Load(object sender, EventArgs e) {
      pageUri = "tcm:1-3-64";
   }
</script>

<asp:Xml DocumentSource="~/navigation.xml" TransformSource="~/breadcrumb.xsl"
        OnLoad="NavigationOnLoad" runat="server" />

And in my code-behind, I have:

   protected string pageUri;

   protected void NavigationOnLoad(object sender, EventArgs e) {
      XsltArgumentList xslArg = new XsltArgumentList();
      xslArg.AddParam("PageUri", "", pageUri);

      ((Xml)sender).TransformArgumentList = xslArg;
   }

There are other ways, maybe more elegant than this, for example using Master pages, but more about that in a later post.

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