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XPathNavigator.Evaluate Method (String)

Evaluates the specified XPath expression and returns the typed result.

Namespace: System.Xml.XPath
Assembly: System.Xml (in system.xml.dll)

public virtual Object Evaluate (
	string xpath
)
public Object Evaluate (
	String xpath
)
public function Evaluate (
	xpath : String
) : Object

Parameters

xpath

A string representing an XPath expression that can be evaluated.

Return Value

The result of the expression (Boolean, number, string, or node set). This maps to Boolean, Double, String, or XPathNodeIterator objects respectively.

Exception typeCondition

ArgumentException

The return type of the XPath expression is a node set.

XPathException

The XPath expression is not valid.

The following C# code converts the Price/text() node to a number, multiplies it by 10, and returns the resulting value.

nav.Evaluate("Price/text()*10");
NoteNote

The XPath position() and last() functions, unless used as a predicate in a location step, require a reference to a node set in order to be evaluated. In this case, you must use the overload which takes an XPathNodeIterator as an argument; otherwise, position() and last() return 0.

This method has no effect on the state of the XPathNavigator.

The following example evaluates an XPath expression and returns a Double.

XPathDocument document = new XPathDocument("books.xml");
XPathNavigator navigator = document.CreateNavigator();

Double total = (double)navigator.Evaluate("sum(descendant::book/price)");
Console.WriteLine("Total price for all books: {0}", total.ToString());

The example takes the books.xml file as an input.

<bookstore>
    <book genre="autobiography" publicationdate="1981-03-22" ISBN="1-861003-11-0">
        <title>The Autobiography of Benjamin Franklin</title>
        <author>
            <first-name>Benjamin</first-name>
            <last-name>Franklin</last-name>
        </author>
        <price>8.99</price>
    </book>
    <book genre="novel" publicationdate="1967-11-17" ISBN="0-201-63361-2">
        <title>The Confidence Man</title>
        <author>
            <first-name>Herman</first-name>
            <last-name>Melville</last-name>
        </author>
        <price>11.99</price>
    </book>
    <book genre="philosophy" publicationdate="1991-02-15" ISBN="1-861001-57-6">
        <title>The Gorgias</title>
        <author>
            <name>Plato</name>
        </author>
        <price>9.99</price>
    </book>
</bookstore>

Windows 98, Windows 2000 SP4, Windows Millennium Edition, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

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

.NET Framework

Supported in: 2.0, 1.1, 1.0

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