Home Library Learn Downloads Support Community
Sign in | United States - English | |
This topic has not yet been rated - Rate this topic

XPathNavigator.Evaluate Method (String)

.NET Framework 4.5

[This documentation is for preview only, and is subject to change in later releases. Blank topics are included as placeholders.]

Evaluates the specified XPath expression and returns the typed result.

Namespace:  System.Xml.XPath
Assembly:  System.Xml (in System.Xml.dll)
C#
C++
F#
VB
Copy 
public virtual Object Evaluate(
	string xpath
)

Parameters

xpath
Type: System.String

A string representing an XPath expression that can be evaluated.

Return Value

Type: System.Object
The result of the expression (Boolean, number, string, or node set). This maps to Boolean, Double, String, or XPathNodeIterator objects respectively.
Exception Condition
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.

Copy 
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.

C#
C++
VB
Copy 

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.

None
Copy 

<?xml version="1.0" encoding="utf-8" ?> 
<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>

.NET Framework

Supported in: 4.5, 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 8 Consumer Preview, Windows Server 8 Beta, Windows 7, Windows Server 2008 SP2, 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.

Did you find this helpful?
(1500 characters remaining)