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XmlNode.SelectSingleNode Method (String)

Selects the first XmlNode that matches the XPath expression.

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

public XmlNode SelectSingleNode(
	string xpath
)

Parameters

xpath
Type: System.String

The XPath expression.

Return Value

Type: System.Xml.XmlNode
The first XmlNode that matches the XPath query or null if no matching node is found. The XmlNode should not be expected to be connected "live" to the XML document. That is, changes that appear in the XML document may not appear in the XmlNode, and vice versa.

ExceptionCondition
XPathException

The XPath expression contains a prefix.

If the XPath expression requires namespace resolution, you must use the SelectSingleNode overload which takes an XmlNamespaceManager as its argument. The XmlNamespaceManager is used to resolve namespaces.

NoteNote:

If the XPath expression does not include a prefix, it is assumed that the namespace URI is the empty namespace. If your XML includes a default namespace, you must still use the XmlNamespaceManager and add a prefix and namespace URI to it; otherwise, you will not get a selected node. For more information, see Select Nodes Using XPath Navigation.

NoteNote:

A common issue when formulating XPath expressions is how to include a single quote (') or double quote (") in the expression. If you have to search for a value that includes a single quote, you must enclose the string in double quotes. If you need to search for a value that includes a double quote, you must enclose the string in single quotes.

For example, suppose you have the following XML:

 <bookstore>
   <book>
     <title>&apos;Emma&apos;</title>
   </book>
 </bookstore>

The following Visual Basic code selects an element that contains single quotes:

 book = root.SelectSingleNode("descendant::book[title=""'Emma'""]")

This method is a Microsoft extension to the Document Object Model (DOM).

The following example changes the price of the first Jane Austen book.

using System;
using System.IO;
using System.Xml;

public class Sample {

  public static void Main() {

    XmlDocument doc = new XmlDocument();
    doc.Load("booksort.xml");

    XmlNode book;
    XmlNode root = doc.DocumentElement;

    book=root.SelectSingleNode("descendant::book[author/last-name='Austen']");

    //Change the price on the book.
    book.LastChild.InnerText="15.95";

    Console.WriteLine("Display the modified XML document....");
    doc.Save(Console.Out);    
  }
}
#using <mscorlib.dll>
#using <System.Xml.dll>
using namespace System;
using namespace System::IO;
using namespace System::Xml;

int main()
{
    XmlDocument* doc = new XmlDocument();
    doc->Load(S"booksort.xml");

    XmlNode* book;
    XmlNode* root = doc->DocumentElement;

    book=root->SelectSingleNode(S"descendant::book[author/last-name='Austen']");

    //Change the price on the book.
    book->LastChild->InnerText=S"15.95";

    Console::WriteLine(S"Display the modified XML document....");
    doc->Save(Console::Out);    
}

The example uses the file, booksort.xml, as input.

<?xml version="1.0"?>
<!-- A fragment of a book store inventory database -->
<bookstore xmlns:bk="urn:samples">
  <book genre="novel" publicationdate="1997" bk:ISBN="1-861001-57-8">
    <title>Pride And Prejudice</title>
    <author>
      <first-name>Jane</first-name>
      <last-name>Austen</last-name>
    </author>
    <price>24.95</price>
  </book>
  <book genre="novel" publicationdate="1992" bk:ISBN="1-861002-30-1">
    <title>The Handmaid's Tale</title>
    <author>
      <first-name>Margaret</first-name>
      <last-name>Atwood</last-name>
    </author>
    <price>29.95</price>
  </book>
  <book genre="novel" publicationdate="1991" bk:ISBN="1-861001-57-6">
    <title>Emma</title>
    <author>
      <first-name>Jane</first-name>
      <last-name>Austen</last-name>
    </author>
    <price>19.95</price>
  </book>
  <book genre="novel" publicationdate="1982" bk:ISBN="1-861001-45-3">
    <title>Sense and Sensibility</title>
    <author>
      <first-name>Jane</first-name>
      <last-name>Austen</last-name>
    </author>
    <price>19.95</price>
  </book>
</bookstore>

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, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC, Xbox 360, Zune

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.

.NET Framework

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

.NET Compact Framework

Supported in: 3.5, 2.0

XNA Framework

Supported in: 3.0, 2.0, 1.0

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