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)
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.XmlNodeThe first XmlNode that matches the XPath query or a 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.
| Exception | Condition |
|---|---|
| XPathException | The XPath expression contains a prefix which is not defined in the XmlNamespaceManager. |
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.
.gif?cs-save-lang=1&cs-lang=fsharp "Note") 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>'Emma'</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).
The following example selects the book with the matching ISBN value.
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 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)
The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.
