Extensions.XPathEvaluate Extensions.XPathEvaluate Extensions.XPathEvaluate Extensions.XPathEvaluate Method

Definition

Evaluates an XPath expression.

Overloads

XPathEvaluate(XNode, String) XPathEvaluate(XNode, String) XPathEvaluate(XNode, String) XPathEvaluate(XNode, String)

Evaluates an XPath expression.

XPathEvaluate(XNode, String, IXmlNamespaceResolver) XPathEvaluate(XNode, String, IXmlNamespaceResolver) XPathEvaluate(XNode, String, IXmlNamespaceResolver) XPathEvaluate(XNode, String, IXmlNamespaceResolver)

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

Remarks

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.

XPathEvaluate(XNode, String) XPathEvaluate(XNode, String) XPathEvaluate(XNode, String) XPathEvaluate(XNode, String)

Evaluates an XPath expression.

public:
[System::Runtime::CompilerServices::Extension]
 static System::Object ^ XPathEvaluate(System::Xml::Linq::XNode ^ node, System::String ^ expression);
[System.Runtime.TargetedPatchingOptOut("Performance critical to inline this type of method across NGen image boundaries")]
public static object XPathEvaluate (this System.Xml.Linq.XNode node, string expression);
static member XPathEvaluate : System.Xml.Linq.XNode * string -> obj
<Extension()>
Public Function XPathEvaluate (node As XNode, expression As String) As Object
Parameters
node
XNode XNode XNode XNode

The XNode on which to evaluate the XPath expression.

expression
String String String String

A String that contains an XPath expression.

Returns

An object that can contain a bool, a double, a string, or an IEnumerable<T>.

Examples

The following example creates a small XML tree with an attribute, then uses the XPathEvaluate method to retrieve the attribute.


                String xml = "<root a='value'/>";  
XDocument d = XDocument.Parse(xml);  
IEnumerable att = (IEnumerable)d.XPathEvaluate("/root/@a");  
Console.WriteLine(att.Cast<XAttribute>().FirstOrDefault());  

                Dim d As XDocument = _  
    <?xml version='1.0'?>  
    <root a='value'/>  
Dim att As IEnumerable = CType(d.XPathEvaluate("/root/@a"), IEnumerable)  
Console.WriteLine(att.Cast(Of XAttribute)().FirstOrDefault())  

This example produces the following output:

a="value"  

Remarks

If the collection is an enumeration of elements or attributes, you can use the Cast operator to get a collection of XElement or XAttribute.

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.

XPathEvaluate(XNode, String, IXmlNamespaceResolver) XPathEvaluate(XNode, String, IXmlNamespaceResolver) XPathEvaluate(XNode, String, IXmlNamespaceResolver) XPathEvaluate(XNode, String, IXmlNamespaceResolver)

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

public:
[System::Runtime::CompilerServices::Extension]
 static System::Object ^ XPathEvaluate(System::Xml::Linq::XNode ^ node, System::String ^ expression, System::Xml::IXmlNamespaceResolver ^ resolver);
public static object XPathEvaluate (this System.Xml.Linq.XNode node, string expression, System.Xml.IXmlNamespaceResolver resolver);
static member XPathEvaluate : System.Xml.Linq.XNode * string * System.Xml.IXmlNamespaceResolver -> obj
<Extension()>
Public Function XPathEvaluate (node As XNode, expression As String, resolver As IXmlNamespaceResolver) As Object
Parameters
node
XNode XNode XNode XNode

The XNode on which to evaluate the XPath expression.

expression
String String String String

A String that contains an XPath expression.

Returns

An object that contains the result of evaluating the expression. The object can be a bool, a double, a string, or an IEnumerable<T>.

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.


                string markup =  
@"<aw:Root xmlns:aw='http://www.adventure-works.com'>  
    <aw:Child1 aw:Att='attdata'>child one data 1</aw:Child1>  
</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");  
IEnumerable atts = (IEnumerable)root.XPathEvaluate("./aw:Child1/@aw:Att", namespaceManager);  
IEnumerable<XAttribute> attList = atts.Cast<XAttribute>();  
XAttribute att = attList.First();  
Console.WriteLine(att);  

                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"  

Remarks

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.

Applies to