XPathNodeIterator Class (System.Xml.XPath)

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.NET Framework Class Library

XPathNodeIterator Class

Provides an iterator over a selected set of nodes.

Namespace: System.Xml.XPath
Assembly: System.Xml (in System.Xml.dll)

Syntax

Visual Basic (Declaration)

Public MustInherit Class XPathNodeIterator _
	Implements ICloneable, IEnumerable

Visual Basic (Usage)

Dim instance As XPathNodeIterator

public abstract class XPathNodeIterator : ICloneable, 
	IEnumerable

Visual C++

public ref class XPathNodeIterator abstract : ICloneable, 
	IEnumerable

JScript

public abstract class XPathNodeIterator implements ICloneable, IEnumerable

Remarks

An XPathNodeIterator object returned by the XPathNavigator class is not positioned on the first node in a selected set of nodes. A call to the MoveNext method of the XPathNodeIterator class must be made to position the XPathNodeIterator object on the first node in the selected set of nodes.

When using the XPathNodeIterator, if you edit the current node or any of its ancestors, your current position is lost. If you want to edit a number of nodes that you have selected, create a XPathNavigator array, copy all of the nodes from the XPathNodeIterator into the array, then iterate through the array and modify the nodes.

There are two ways to iterate over an XPathNavigator collection by using the XPathNodeIterator class.

One way is to use MoveNext and then call Current to get the current XPathNavigator instance, as in the following example:

Visual Basic

While nodeIterator.MoveNext()
    Dim n As XPathNavigator = nodeIterator.Current
    Console.WriteLine(n.LocalName)
End While

while (nodeIterator.MoveNext())
{
    XPathNavigator n = nodeIterator.Current;
    Console.WriteLine(n.LocalName);
}

Visual C++

        while (nodeIterator->MoveNext())
        {
            XPathNavigator^ n = nodeIterator->Current;
	    Console::WriteLine(n->LocalName);
        }

Another way is to use a foreach loop to call GetEnumerator and use the returned IEnumerator interface to enumerate the nodes, as in the following example:

Visual Basic

For Each n As XPathNavigator In nodeIterator
    Console.WriteLine(nav.LocalName)
Next

foreach (XPathNavigator n in nodeIterator)
    Console.WriteLine(n.LocalName);

Visual C++

        for each (XPathNavigator^ n in nodeIterator)
	    Console::WriteLine(n->LocalName);

You should either use MoveNext and Current or use GetEnumerator. Combining these two approaches can cause unexpected results. For example, if the MoveNext is called first, and then GetEnumerator is called in the foreach loop, the foreach loop will not start enumerating the results from the beginning of the collection, but from the position after the Current method.

Notes to Inheritors:

When you inherit from the XPathNodeIterator class, you must override the following members:

Examples

The following example uses the Select method of the XPathNavigator class to select a node set using the XPathNodeIterator class.

Visual Basic

Dim document As XPathDocument = New XPathDocument("books.xml")
Dim navigator As XPathNavigator = document.CreateNavigator()

Dim nodes As XPathNodeIterator = navigator.Select("/bookstore/book")
nodes.MoveNext()
Dim nodesNavigator As XPathNavigator = nodes.Current

Dim nodesText As XPathNodeIterator = nodesNavigator.SelectDescendants(XPathNodeType.Text, False)

While nodesText.MoveNext()
    Console.WriteLine(nodesText.Current.Value)
End While

XPathDocument document = new XPathDocument("books.xml");
XPathNavigator navigator = document.CreateNavigator();

XPathNodeIterator nodes = navigator.Select("/bookstore/book");
nodes.MoveNext();
XPathNavigator nodesNavigator = nodes.Current;

XPathNodeIterator nodesText = nodesNavigator.SelectDescendants(XPathNodeType.Text, false);

while (nodesText.MoveNext())
    Console.WriteLine(nodesText.Current.Value);

Visual C++

XPathDocument^ document = gcnew XPathDocument("books.xml");
XPathNavigator^ navigator = document->CreateNavigator();

XPathNodeIterator^ nodes = navigator->Select("/bookstore/book");
nodes->MoveNext();
XPathNavigator^ nodesNavigator = nodes->Current;

XPathNodeIterator^ nodesText = nodesNavigator->SelectDescendants(XPathNodeType::Text, false);

while (nodesText->MoveNext())
	Console::WriteLine(nodesText->Current->Value);

The example takes the books.xml file as input.

<bookstore>
    <book genre="autobiography" publicationdate="1981-03-22" ISBN="1-861003-11-0">
        <title>The Autobiography of Benjamin Franklin</title>
        <author>
            <first-name>Benjamin</first-name>
            <last-name>Franklin</last-name>
        </author>
        <price>8.99</price>
    </book>
    <book genre="novel" publicationdate="1967-11-17" ISBN="0-201-63361-2">
        <title>The Confidence Man</title>
        <author>
            <first-name>Herman</first-name>
            <last-name>Melville</last-name>
        </author>
        <price>11.99</price>
    </book>
    <book genre="philosophy" publicationdate="1991-02-15" ISBN="1-861001-57-6">
        <title>The Gorgias</title>
        <author>
            <name>Plato</name>
        </author>
        <price>9.99</price>
    </book>
</bookstore>

Inheritance Hierarchy

System.Object
System.Xml.XPath.XPathNodeIterator

Thread Safety

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

Platforms

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

Version Information

.NET Framework

Supported in: 3.5, 3.0, 2.0, 1.1, 1.0

Reference

XPathNodeIterator Members

System.Xml.XPath Namespace

Community Content

cheeso

Handy tool for visualizing results

It's one thing to understand the programming interface for using the XPathNodeIterator and XPathNavigator. It's another thing to be productive in authoring correct XPath expressions.

If you are developing with XPath, you may want some help building those XPath expressions. There's a handy tool to help you : XPathVisualizer, available on http://xpathvisualizer.codeplex.com. A Free download. It lets you see the matched nodes, given an XML document and an XPath expression. It also gives you "red squigglies" within XPath expressions that don't compile, pinpointing the problem. I found the tool invaluable when tweaking my XPathExpressions to get them just right.

cheeso

You can use foreach

  XmlDocument doc = new XmlDocument();
doc.Load("orders.xml");
XPathNavigator nav = doc.CreateNavigator();
foreach (XPathNavigator node in nav.Select("/orders/order"))
    Console.WriteLine(node.Value);