Extensions.XPathEvaluate Method (XNode, String, IXmlNamespaceResolver)

Evaluates an XPath expression, resolving namespace prefixes using the specified IXmlNamespaceResolver.

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

'Declaration
<ExtensionAttribute> _
Public Shared Function XPathEvaluate ( _
	node As XNode, _
	expression As String, _
	resolver As IXmlNamespaceResolver _
) As Object

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

A IXmlNamespaceResolver for the namespace prefixes in the XPath expression.

Return Value

Type: System.Object
An object that contains the result of evaluating the expression. The object can be a bool, a double, a string, or an IEnumerable(Of T).

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).

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

Although the ordering of returned collections is not specified in the XML XPath Language 1.0 Recommendation, this extension method returns nodes in document order.

Note that nodes are returned in document order even when you use a reverse axis, such as preceding-sibling or ancestor-or-self.

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.

Dim markup As XElement = _
    <aw:Root xmlns:aw='http://www.adventure-works.com'>
        <aw:Child1 aw:Att='attdata'>child one data 1</aw:Child1>
    </aw:Root>
Dim reader As XmlReader = markup.CreateReader
Dim nameTable As XmlNameTable = reader.NameTable
Dim namespaceManager As XmlNamespaceManager = New XmlNamespaceManager(nameTable)
namespaceManager.AddNamespace("aw", "http://www.adventure-works.com")
Dim atts As IEnumerable = CType(markup.XPathEvaluate("./aw:Child1/@aw:Att", namespaceManager), IEnumerable)
Dim attList As IEnumerable(Of XAttribute) = atts.Cast(Of XAttribute)()
Dim att As XAttribute = attList.First()
Console.WriteLine(att)

This example produces the following output:

aw:Att="attdata"

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5

.NET Framework Client Profile

Supported in: 4, 3.5 SP1
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