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XPathNodeIterator in Transformations 

The XPathNodeIterator provides methods to iterate over a set of nodes created as the result of an XML Path Language (XPath) query or a result tree fragment converted to a node set by use of the node-set method. The XPathNodeIterator enables you to iterate over the nodes within that node set. Once a node set is retrieved, the XPathNodeIterator class provides a read-only, forward-only cursor to the selected set of nodes. The node set is created in document order, so calling this method moves to the next node in document order. XPathNodeIterator does not build a node tree of all the nodes in the set. Instead, it provides a single node window into the data, exposing the underlying node it points to as you move around in the tree. The methods and properties available from the XPathNodeIterator class enable you to get information from the current node. For a list of the available methods and properties, see XPathNodeIterator Members.

Since an XPathNodeIterator moves over a set of nodes created from an XPath query and moves forward only, the way to move is by using the MoveNext method. The return type of this method is Boolean, returning true if it moves to the next selected node, and false if there are no more selected nodes. If it returns true, the following list shows the properties available:

When you are looking at a node set for the first time, a call to MoveNext must be made to position the XPathNodeIterator on the first node of the selected set. This allows a while loop to be written.

The following code example shows how to pass an XPathNodeIterator to an XslTransform as a parameter in the XsltArgumentList. The input to the code is books.xml, and the style sheet is text.xsl. The file test.xml is the XPathDocument.

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

public class sample
{
    public static void Main()
    {
        XPathDocument Doc = new XPathDocument("books.xml");
        XPathNavigator nav = Doc.CreateNavigator();
        XPathNodeIterator Iterator = nav.Select("/bookstore/book");

        XsltArgumentList arg = new XsltArgumentList();
        arg.AddParam("param1", "", Iterator);

        XslTransform xslt = new XslTransform();
        xslt.Load("test.xsl");

        XPathDocument xd = new XPathDocument("test.xml");

        Stream strmTemp = new FileStream("out.xml", FileMode.Create, FileAccess.ReadWrite);
        xslt.Transform(xd, arg, strmTemp, null);
    }
}

books.xml

<?xml version='1.0'?>
<!-- This file represents a fragment of a book store inventory database. -->
<bookstore specialty="novel">
    <book style="autobiography">
    <title>Seven Years in Trenton</title>
        <author>
            <first-name>Jay</first-name>
            <last-name>Adams</last-name>
            <award>Trenton Literary Review Honorable Mention</award>
            <country>USA</country>
        </author>
        <price>12</price>
    </book>
    <book style="textbook">
        <title>History of Trenton</title>
        <author>
            <first-name>Kim</first-name>
            <last-name>Akers</last-name>
            <publication>
                Selected Short Stories of
                <first-name>Scott</first-name>
                <last-name>Bishop</last-name>
                <country>US</country>
            </publication>
        </author>
        <price>55</price>
    </book>
</bookstore>

test.xsl

<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:msxsl="urn:schemas-microsoft-com:xslt" exclude-result-prefixes="msxsl">

<xsl:output method="xml" indent="yes"/>
<xsl:param name="param1"/>

<xsl:template match="/">
    <out>
        <xsl:for-each select="$param1/title">
            <title><xsl:value-of select="."/></title>
        </xsl:for-each>
    </out>
</xsl:template>

</xsl:stylesheet>

test.xml

<Title attr="Test">this is a test</Title>

Output (out.xml)

<?xml version="1.0" encoding="utf-8"?>
<out>
  <title>Seven Years in Trenton</title>
  <title>History of Trenton</title>
</out>

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