XPathNavigator.Evaluate Method (String, IXmlNamespaceResolver)
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Evaluates the specified XPath expression and returns the typed result, using the IXmlNamespaceResolver object specified to resolve namespace prefixes in the XPath expression.
Namespace: System.Xml.XPath
Assembly: System.Xml (in System.Xml.dll)
Parameters
- xpath
- Type: System.String
A string representing an XPath expression that can be evaluated.
- resolver
- Type: System.Xml.IXmlNamespaceResolver
The IXmlNamespaceResolver object used to resolve namespace prefixes in the XPath expression.
Return Value
Type: System.ObjectThe 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 returns a number after converting the Price/text() node to a number and multiplying the value by 10.
XPathExpression expr = nav.Compile("Price/text()*10");
nav.Evaluate(expr);
 Note |
|---|
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 using the XmlNamespaceManager object specified to resolve namespace prefixes in the XPath expression.
XPathDocument document = new XPathDocument("contosoBooks.xml"); XPathNavigator navigator = document.CreateNavigator(); XmlNamespaceManager manager = new XmlNamespaceManager(navigator.NameTable); manager.AddNamespace("bk", "http://www.contoso.com/books"); Double total = (double)navigator.Evaluate("sum(descendant::bk:book/bk:price)", manager); Console.WriteLine("Total price for all books: {0}", total.ToString());
The example takes the contosoBooks.xml file as an input.
<?xml version="1.0" encoding="utf-8" ?>
<bookstore xmlns="http://www.contoso.com/books">
<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 8 Release Preview, Windows Server 2012, Windows 7, Windows Vista SP2, 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.
