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XsltArgumentList for Style Sheet Parameters and Extension Objects

XsltArgumentList for Style Sheet Parameters and Extension Objects

The XsltArgumentList class contains Extensible Stylesheet Language for Transformations (XSLT) parameters and XSLT extension objects. When passed into the Transform method, these parameters and extension objects can be invoked from style sheets.

Note Note

The XslTransform and XsltArgumentList classes are obsolete in the .NET Framework 2.0. You can perform XSLT transformations using the XslCompiledTransform class. See Using the XslCompiledTransform Class and Migrating From the XslTransform Class for more information.

The XsltArgumentList class contains XSLT parameters and XSLT extension objects. When passed into the Transform method, these parameters and extension objects can be invoked from style sheets.

The following are advantages to passing an object rather than using an embedded script:

  • Provides better encapsulation and reuse of classes.

  • Allows style sheets to be smaller and more maintainable.

  • Supports calling methods on classes belonging to namespaces other than those defined within the set of supported System namespaces.

  • Supports passing result tree fragments to the style sheet with the use of the XPathNodeIterator.

XSLT parameters are added to the XsltArgumentList using the AddParam method. A qualified name and namespace Uniform Resource Identifier (URI) are associated with the parameter object at that time.

The parameter object should correspond to a World Wide Web Consortium (W3C) type. The following table shows the corresponding W3C types, the equivalent .NET Framework classes (type), and whether the W3C type is an XML Path Language (XPath) type or XSLT type.

W3C Type

Equivalent .NET Framework class (type)

XPath type or XSLT type

String

System.String

XPath

Boolean

System.Boolean

XPath

Number

System.Double

XPath

Result Tree Fragment

System.Xml.XPath.XPathNavigator

XSLT

Node Set

System.Xml.XPath.XPathNodeIterator

XPath

If the parameter object is not one of the above classes, it is forced to either a Double or String, as appropriate. Int16, UInt16, Int32, UInt32, Int64, UInt64, Single and Decimal types are forced to a Double. All other types are forced to a String using the ToString method.

To use the XSLT parameter, the user needs to do the following:

  1. Create an XsltArgumentList and add the objects using AddParam.

  2. Call the parameters from the style sheet.

  3. Pass the XsltArgumentList to the Transform method.

The following example uses the AddParam method to create a parameter to hold a calculated discount date. The discount date is calculated to be 20 days from the order date.

using System;
using System.IO;
using System.Xml;
using System.Xml.XPath;
using System.Xml.Xsl;

public class Sample
{
   private const String filename = "order.xml";
   private const String stylesheet = "discount.xsl";

   public static void Main() {

    //Create the XslTransform and load the style sheet.
    XslTransform xslt = new XslTransform();
    xslt.Load(stylesheet);

    //Load the XML data file.
    XPathDocument doc = new XPathDocument(filename);

    //Create an XsltArgumentList.
    XsltArgumentList xslArg = new XsltArgumentList();
         
    //Calculate the discount date.
    DateTime today = DateTime.Now;
    DateTime d = today.AddDays(20);
    xslArg.AddParam("discount", "", d.ToString());

    //Create an XmlTextWriter to handle the output.
    XmlTextWriter writer = new XmlTextWriter("orderout.xml", null);

    //Transform the file.
    xslt.Transform(doc, xslArg, writer, null);
    writer.Close();
  }
}

order.xml

<!--Represents a customer order-->
<order>
  <book ISBN='10-861003-324'>
    <title>The Handmaid's Tale</title>
    <price>19.95</price>
  </book>
  <cd ISBN='2-3631-4'>
    <title>Americana</title>
    <price>16.95</price>
  </cd>
</order>

discount.xsl

<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
  <xsl:param name="discount"/>
  <xsl:template match="/">
    <order>
      <xsl:variable name="sub-total" select="sum(//price)"/>
      <total><xsl:value-of select="$sub-total"/></total>
      15% discount if paid by: <xsl:value-of select="$discount"/>
    </order>
  </xsl:template>
</xsl:stylesheet>

<order>
   <total>36.9</total> 
   15% discount if paid by: 5/6/2001 5:01:15 PM 
</order>

XSLT extension objects are added to the XsltArgumentList using the AddExtensionObject method. A qualified name and namespace URI are associated with the extension object at that time.

When an object is added, the caller of the AddExtensionObject must be fully trusted in the security policy. If the caller is semi-trusted, the addition will fail.

Though an object is added successfully, it does not guarantee that the execution will be successful. When the Transform method is called, permissions are calculated against the evidence provided at Load time, and that permission set is assigned to the entire transformation process. If an extension object attempts to initiate an action that requires permissions not found in the set, an exception is thrown.

The data types returned from extension objects are one of the four basic XPath data types of number, string, Boolean, and node set.

To use the XSLT extension object, the user needs to do the following:

  1. Create an XsltArgumentList and add the extension object using AddExtensionObject.

  2. Invoke the extension object from the style sheet.

  3. Pass the XsltArgumentList to the Transform method.

The following example calculates the circumference of a circle given its radius.

using System;
using System.IO;
using System.Xml;
using System.Xml.XPath;
using System.Xml.Xsl;


public class Sample
{
   private const String filename = "number.xml";
   private const String stylesheet = "circle.xsl";

   public static void Main() {

        Sample test = new Sample();
    }
    
  public Sample() {

    //Create the XslTransform and load the style sheet.
    XslTransform xslt = new XslTransform();
    xslt.Load(stylesheet);

    //Load the XML data file.
    XPathDocument doc = new XPathDocument(filename);

    //Create an XsltArgumentList.
    XsltArgumentList xslArg = new XsltArgumentList();
         
    //Add an object to calculate the circumference of the circle.
    Calculate obj = new Calculate();
    xslArg.AddExtensionObject("urn:myObj", obj);

    //Create an XmlTextWriter to output to the console.
    XmlTextWriter writer = new XmlTextWriter(Console.Out);

    //Transform the file.
    xslt.Transform(doc, xslArg, writer, null);
    writer.Close();

  }

  //Calculates the circumference of a circle given the radius.
  public class Calculate{

    private double circ = 0;
      
    public double Circumference(double radius){
       circ = Math.PI*2*radius;
       return circ;
    }
  }
}

number.xml

<?xml version='1.0'?>
<data>
  <circle>
    <radius>12</radius>
  </circle>
  <circle>
    <radius>37.5</radius>
  </circle>
</data>  

circle.xsl

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

  <xsl:template match="data">
  <circles>
  <xsl:for-each select="circle">
    <circle>
    <xsl:copy-of select="node()"/>
       <circumference>
          <xsl:value-of select="myObj:Circumference(radius)"/>        
       </circumference>
    </circle>
  </xsl:for-each>
  </circles>
  </xsl:template>
</xsl:stylesheet>

<circles xmlns:myObj="urn:myObj">

<circle>

<radius>12</radius>

<circumference>75.398223686155</circumference>

</circle>

<circle>

<radius>37.5</radius>

<circumference>235.61944901923448</circumference>

</circle>

</circles>

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