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XsltArgumentList for Stylesheet Parameters and Extension Objects

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 other 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 XPathNavigator.

XSLT Style Sheet Parameters

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

The parameter object should correspond to a W3C type. The following table shows the corresponding W3C types, the equivalent .NET classes (Type), and whether the W3C Type is an XPath Type or XSLT Type.

W3C TypeEquivalent .NET Class (Type)XPath Type or XSLT Type
StringSystem.StringXPath
BooleanSystem.BooleanXPath
NumberSystem.DoubleXPath
Result Tree FragmentSystem.Xml.XPath.XPathNavigatorXSLT
Node SetSystem.Xml.XPath.XPathNodeIteratorXPath

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.

Example

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

Imports System
Imports System.IO
Imports System.Xml
Imports System.Xml.XPath
Imports System.Xml.Xsl

Public class Sample

   Private Const filename As String = "order.xml"
   Private Const stylesheet As String = "discount.xsl"

   Public Shared Sub Main()

    'Create the XslTransform and load the stylesheet.
    Dim xslt As XslTransform = New XslTransform
    xslt.Load(stylesheet)

    'Load the XML data file.
    Dim doc As XPathDocument = New XPathDocument(filename)

    'Create an XsltArgumentList.
    Dim xslArg As XsltArgumentList = New XsltArgumentList
         
    'Calculate the discount date.
    Dim today As DateTime = DateTime.Now
    Dim d As DateTime = today.AddDays(20)
    xslArg.AddParam("discount", "", d.ToString())

    'Create an XmlTextWriter to handle the output.             
    Dim writer As XmlTextWriter = New XmlTextWriter("orderout.xml", Nothing)

    'Transform the file.
    xslt.Transform(doc, xslArg, writer, Nothing)

    writer.Close()

  End Sub
End Class
[C#]
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 stylesheet.
    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();
  }
}

Input

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>

Output

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

XSLT Extension Objects

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 transform 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.

Example

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

Imports System
Imports System.IO
Imports System.Xml
Imports System.Xml.XPath
Imports System.Xml.Xsl

Public Class Sample
   Private Const filename As String = "number.xml"
   Private Const stylesheet As String = "circle.xsl"

   Public Shared Sub Main()
        Dim test As Sample = New Sample
   End Sub
    
  Public Sub New()
    'Create the XslTransform and load the stylesheet.
    Dim xslt As XslTransform = New XslTransform
    xslt.Load(stylesheet)

    'Load the XML data file.
    Dim doc As XPathDocument = New XPathDocument(filename)

    'Create an XsltArgumentList.
    Dim xslArg As XsltArgumentList = New XsltArgumentList
         
    'Add an object to calculate the circumference of the circle.
    Dim obj As Calculate = New Calculate
    xslArg.AddExtensionObject("urn:myObj", obj)

    'Create an XmlTextWriter to output to the console.             
    Dim writer As XmlTextWriter = New XmlTextWriter(Console.Out)

    'Transform the file.
    xslt.Transform(doc, xslArg, writer, Nothing)
    writer.Close()

  End Sub

  'Calculates the circumference of a circle given the radius.
  Public Class Calculate

    Private circ As double = 0
      
    Public Function Circumference(radius As Double) As Double
       circ = Math.PI*2*radius
       Return circ
    End Function
  End Class
End Class
[C#]
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 stylesheet.
    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;
    }
  }
}

Input

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>

Output

<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>

See Also

XslTransform Class Implements the XSLT Processor

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