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Extensions.XPathSelectElement Method (XNode, String, IXmlNamespaceResolver)

.NET Framework 4

Other Versions

Selects an XElement using a XPath expression, resolving namespace prefixes using the specified IXmlNamespaceResolver.

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

Syntax

C++

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public static XElement XPathSelectElement(
	this XNode node,
	string expression,
	IXmlNamespaceResolver resolver
)

Parameters

node: Type: System.Xml.Linq.XNode
The XNode on which to evaluate the XPath expression.

expression: Type: System.String
A String that contains an XPath expression.

resolver: Type: System.Xml.IXmlNamespaceResolver
An IXmlNamespaceResolver for the namespace prefixes in the XPath expression.

Return Value

Type: System.Xml.Linq.XElement
An XElement, or null.

Usage Note

In Visual Basic and C#, you can call this method as an instance method on any object of type XNode. When you use instance method syntax to call this method, omit the first parameter. For more information, see Extension Methods (Visual Basic) or Extension Methods (C# Programming Guide).

Remarks

You can use this method to evaluate XPath expressions that contain namespace prefixes.

Examples

The following example creates an XML tree that contains a namespace. It uses an XmlReader to read the XML document. It then gets an XmlNameTable from the XmlReader, and an XmlNamespaceManager from the XmlNameTable. It uses the XmlNamespaceManager when selecting an element.

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string markup = @"
<aw:Root xmlns:aw='http://www.adventure-works.com'>
    <aw:Child1>child one data</aw:Child1>
    <aw:Child2>child two data</aw:Child2>
</aw:Root>";
XmlReader reader = XmlReader.Create(new StringReader(markup));
XElement root = XElement.Load(reader);
XmlNameTable nameTable = reader.NameTable;
XmlNamespaceManager namespaceManager = new XmlNamespaceManager(nameTable);
namespaceManager.AddNamespace("aw", "http://www.adventure-works.com");
XElement child1 = root.XPathSelectElement("./aw:Child1", namespaceManager);
Console.WriteLine(child1);

This example produces the following output:

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<aw:Child1 xmlns:aw="http://www.adventure-works.com">child one data</aw:Child1>

Version Information

.NET Framework

Supported in: 4, 3.5

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Platforms

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

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

Reference

Extensions Class

XPathSelectElement Overload

System.Xml.XPath Namespace

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FAQ

Use different prefix strings to make example clearer

The example would be more useful/clearer if the namespace prefix added to the XmlNamespaceManager used a different prefix string from the original document. The current example code gives the impression that you have to know and use the prefix found in the original document, which is not the case. The whole point of namespace resolution is that the prefixes really don't matter at all, it's the URIs they represent that are significant.

Something like this:

string markup = @"
<aw:Root xmlns:aw='http://www.adventure-works.com'>
<aw:Child1>child one data</aw:Child1>
<aw:Child2>child two data</aw:Child2>
</aw:Root>";
XmlReader reader = XmlReader.Create(new StringReader(markup));
XElement root = XElement.Load(reader);
XmlNameTable nameTable = reader.NameTable;
XmlNamespaceManager namespaceManager = new XmlNamespaceManager(nameTable);
namespaceManager.AddNamespace("ns", "http://www.adventure-works.com");
XElement child1 = root.XPathSelectElement("./ns:Child1", namespaceManager);
Console.WriteLine(child1);

History

11/12/2010
Danny Thorpe