XmlNode.SelectSingleNode Method (String, XmlNamespaceManager) (System.Xml)

SelectSingleNode Method (String, Xm...

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Microsoft Visual Studio 2008/.NET Framework 3.5

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.NET Framework Class Library

XmlNode..::.SelectSingleNode Method (String, XmlNamespaceManager)

Selects the first XmlNode that matches the XPath expression. Any prefixes found in the XPath expression are resolved using the supplied XmlNamespaceManager.

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

Syntax

Visual Basic (Declaration)

Public Function SelectSingleNode ( _
    xpath As String, _
    nsmgr As XmlNamespaceManager _
) As XmlNode

Visual Basic (Usage)

Dim instance As XmlNode
Dim xpath As String
Dim nsmgr As XmlNamespaceManager
Dim returnValue As XmlNode

returnValue = instance.SelectSingleNode(xpath, _
    nsmgr)

public XmlNode SelectSingleNode(
    string xpath,
    XmlNamespaceManager nsmgr
)

Visual C++

public:
XmlNode^ SelectSingleNode(
    String^ xpath, 
    XmlNamespaceManager^ nsmgr
)

JScript

public function SelectSingleNode(
    xpath : String, 
    nsmgr : XmlNamespaceManager
) : XmlNode

Parameters

xpath: Type: System..::.String
The XPath expression.

nsmgr: Type: System.Xml..::.XmlNamespaceManager
An XmlNamespaceManager to use for resolving namespaces for prefixes in the XPath expression.

Return Value

Type: System.Xml..::.XmlNode
The first XmlNode that matches the XPath query or nullNothingnullptra null reference (Nothing in Visual Basic) 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.

Exceptions

Exception	Condition
XPathException	The XPath expression contains a prefix which is not defined in the XmlNamespaceManager.

Remarks

XPath expressions can include namespaces. Namespace resolution is supported using the XmlNamespaceManager. If the XPath expression includes a prefix, the prefix and namespace URI pair must be added to the XmlNamespaceManager.

Note:
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 add a prefix and namespace URI to the XmlNamespaceManager; otherwise, you will not get a node selected. For more information, see Select Nodes Using XPath Navigation.

For example, if you had the following XML:

 <bookstore xmlns="http://www.lucernepublishing.com">
  <book>
    <title>Pride And Prejudice</title>
  </book>
 </bookstore>

The following C# code selects the first book node:

 XmlNamespaceManager nsmgr = new XmlNamespaceManager(doc.NameTable);
 nsmgr.AddNamespace("ab", "http://www.lucernepublishing.com");
 XmlNode book = doc.SelectSingleNode("//ab:book", nsmgr);

Note:
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 xmlns="http://www.lucernepublishing.com">
   <book>
     <title>&apos;Emma&apos;</title>
   </book>
 </bookstore>

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

 Dim nsmgr As XmlNamespaceManager = New XmlNamespaceManager(doc.NameTable)
 nsmgr.AddNamespace("ab", "http://www.lucernepublishing.com")
 book = root.SelectSingleNode("descendant::ab:book[ab:title=""'Emma'""]", nsmgr)

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

Examples

The following example selects the book with the matching ISBN value.

Visual Basic

Imports System
Imports System.IO
Imports System.Xml

public class Sample

  public shared sub Main()

      Dim doc as XmlDocument = new XmlDocument()
      doc.Load("booksort.xml")

      'Create an XmlNamespaceManager for resolving namespaces.
      Dim nsmgr as XmlNamespaceManager = new XmlNamespaceManager(doc.NameTable)
      nsmgr.AddNamespace("bk", "urn:samples")

      'Select the book node with the matching attribute value.
      Dim book as XmlNode 
      Dim root as XmlElement = doc.DocumentElement
      book = root.SelectSingleNode("descendant::book[@bk:ISBN='1-861001-57-6']", nsmgr)

      Console.WriteLine(book.OuterXml)

  end sub
end class

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

public class Sample
{
  public static void Main()
  {

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

      //Create an XmlNamespaceManager for resolving namespaces.
      XmlNamespaceManager nsmgr = new XmlNamespaceManager(doc.NameTable);
      nsmgr.AddNamespace("bk", "urn:samples");

      //Select the book node with the matching attribute value.
      XmlNode book;
      XmlElement root = doc.DocumentElement;
      book = root.SelectSingleNode("descendant::book[@bk:ISBN='1-861001-57-6']", nsmgr);

      Console.WriteLine(book.OuterXml);

  }
}

Visual C++

#using <System.Xml.dll>

using namespace System;
using namespace System::IO;
using namespace System::Xml;
int main()
{
   XmlDocument^ doc = gcnew XmlDocument;
   doc->Load( "booksort.xml" );

   //Create an XmlNamespaceManager for resolving namespaces.
   XmlNamespaceManager^ nsmgr = gcnew XmlNamespaceManager( doc->NameTable );
   nsmgr->AddNamespace( "bk", "urn:samples" );

   //Select the book node with the matching attribute value.
   XmlNode^ book;
   XmlElement^ root = doc->DocumentElement;
   book = root->SelectSingleNode( "descendant::book->Item[@bk:ISBN='1-861001-57-6']", nsmgr );
   Console::WriteLine( book->OuterXml );
}

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>

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, 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.

Version Information

.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

Reference

XmlNode Class

XmlNode Members

SelectSingleNode Overload

System.Xml Namespace