XPathExpression Class

Definition

Namespace:

System.Xml.XPath

Assemblies:

netstandard.dll, System.Xml.ReaderWriter.dll

Source:

XPathExpr.cs

Provides a typed class that represents a compiled XPath expression.

C#

public abstract class XPathExpression

Inheritance

Object

XPathExpression

Examples

The following example shows how to use the XPath return type to determine how to process the XPath expression.

C#

using System;
using System.Xml;
using System.Xml.XPath;

public class XPathExpressionExample
{
    public static void Main()
    {
        XPathDocument document = new XPathDocument("contosoBooks.xml");
        XPathNavigator navigator = document.CreateNavigator();

        XPathExpression expression1 = XPathExpression.Compile(".//bk:price/text()*10"); // Returns a number.
        XPathExpression expression2 = XPathExpression.Compile("bk:bookstore/bk:book/bk:price"); // Returns a nodeset.

        XmlNamespaceManager manager = new XmlNamespaceManager(navigator.NameTable);
        manager.AddNamespace("bk", "http://www.contoso.com/books");

        expression1.SetContext(manager);
        expression2.SetContext(manager);

        Evaluate(expression1, navigator);
        Evaluate(expression2, navigator);
    }

    public static void Evaluate(XPathExpression expression, XPathNavigator navigator)
    {
        switch (expression.ReturnType)
        {
            case XPathResultType.Number:
                Console.WriteLine(navigator.Evaluate(expression));
                break;

            case XPathResultType.NodeSet:
                XPathNodeIterator nodes = navigator.Select(expression);
                while (nodes.MoveNext())
                {
                    Console.WriteLine(nodes.Current.ToString());
                }
                break;

            case XPathResultType.Boolean:
                if ((bool)navigator.Evaluate(expression))
                    Console.WriteLine("True!");
                break;

            case XPathResultType.String:
                Console.WriteLine(navigator.Evaluate(expression));
                break;
        }
    }
}

The example takes the contosoBooks.xml file as input.

XML

<?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>  

Remarks

This class is returned as the result of the Compile method of the XPathNavigator class. It is a parameter to the Evaluate, Matches, Select, and SelectSingleNode methods of the XPathNavigator class.

Notes to Implementers

When you inherit from the XPathExpression class, you must override the following members:

• AddSort(Object, IComparer)AddSort(Object, XmlSortOrder, XmlCaseOrder, String, XmlDataType)

• Clone()

• Expression

• ReturnType

• SetContext(IXmlNamespaceResolver)

• SetContext(XmlNamespaceManager).

Properties

Expression	When overridden in a derived class, gets a string representation of the XPathExpression.
ReturnType	When overridden in a derived class, gets the result type of the XPath expression.

Methods

AddSort(Object, IComparer)	When overridden in a derived class, sorts the nodes selected by the XPath expression according to the specified IComparer object.
AddSort(Object, XmlSortOrder, XmlCaseOrder, String, XmlDataType)	When overridden in a derived class, sorts the nodes selected by the XPath expression according to the supplied parameters.
Clone()	When overridden in a derived class, returns a clone of this XPathExpression.
Compile(String, IXmlNamespaceResolver)	Compiles the specified XPath expression, with the IXmlNamespaceResolver object specified for namespace resolution, and returns an XPathExpression object that represents the XPath expression.
Compile(String)	Compiles the XPath expression specified and returns an XPathExpression object representing the XPath expression.
Equals(Object)	Determines whether the specified object is equal to the current object. (Inherited from Object)
GetHashCode()	Serves as the default hash function. (Inherited from Object)
GetType()	Gets the Type of the current instance. (Inherited from Object)
MemberwiseClone()	Creates a shallow copy of the current Object. (Inherited from Object)
SetContext(IXmlNamespaceResolver)	When overridden in a derived class, specifies the IXmlNamespaceResolver object to use for namespace resolution.
SetContext(XmlNamespaceManager)	When overridden in a derived class, specifies the XmlNamespaceManager object to use for namespace resolution.
ToString()	Returns a string that represents the current object. (Inherited from Object)

Applies to