XPathExpression XPathExpression XPathExpression XPathExpression Class

Definition

Provides a typed class that represents a compiled XPath expression.

public ref class XPathExpression abstract
public abstract class XPathExpression
type XPathExpression = class
Public MustInherit Class XPathExpression
Inheritance
XPathExpressionXPathExpressionXPathExpressionXPathExpression

Examples

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

public ref class Sample
{
public:
   static void Evaluate( XPathExpression^ expr, XPathNavigator^ nav )
   {
      XPathNodeIterator^ i = nav->Select(expr);
      switch ( expr->ReturnType )
      {
         case XPathResultType::Number:
            Console::WriteLine( nav->Evaluate( expr ) );
            break;

         case XPathResultType::NodeSet:
            while ( i->MoveNext() )
                        Console::WriteLine( i->Current );
            break;

         case XPathResultType::Boolean:
            if ( *safe_cast<bool^>(nav->Evaluate( expr )) )
                        Console::WriteLine( "True!" );
            break;

         case XPathResultType::String:
            Console::WriteLine( nav->Evaluate( expr ) );
            break;
      }
   }

};

int main()
{
   XPathDocument^ doc = gcnew XPathDocument( "contosoBooks.xml" );
   XPathNavigator^ nav = doc->CreateNavigator();
   XPathExpression^ expr1 = nav->Compile( ".//price/text()*10" ); // Returns a number.

   XPathExpression^ expr2 = nav->Compile( "bookstore/book/price" ); // Returns a nodeset.

   Sample^ MySample = gcnew Sample;
   MySample->Evaluate( expr1, nav );
   MySample->Evaluate( expr2, nav );
}

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;
        }
    }
}
Imports System
Imports System.Xml
Imports System.Xml.XPath

Public Class XPathExpressionExample

    Public Shared Sub Main()
        Dim document As XPathDocument = New XPathDocument("contosoBooks.xml")
        Dim navigator As XPathNavigator = document.CreateNavigator()

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

        Dim manager As XmlNamespaceManager = New XmlNamespaceManager(navigator.NameTable)
        manager.AddNamespace("bk", "http://www.contoso.com/books")

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

        Evaluate(expression1, navigator)
        Evaluate(expression2, navigator)

    End Sub

    Public Shared Sub Evaluate(ByVal expression As XPathExpression, ByVal navigator As XPathNavigator)

        Select Case expression.ReturnType
            Case XPathResultType.Number
                Console.WriteLine(navigator.Evaluate(expression))
                Exit Sub

            Case XPathResultType.NodeSet
                Dim nodes As XPathNodeIterator = navigator.Select(expression)
                While nodes.MoveNext()
                    Console.WriteLine(nodes.Current.ToString())
                End While

            Case XPathResultType.Boolean
                If CType(navigator.Evaluate(expression), Boolean) Then
                    Console.WriteLine("True!")
                End If

            Case XPathResultType.String
                Console.WriteLine(navigator.Evaluate(expression))
        End Select

    End Sub
End Class

The example takes the contosoBooks.xml file as 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>  

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 Inheritors

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

Properties

Expression Expression Expression Expression

When overridden in a derived class, gets a string representation of the XPathExpression.

ReturnType ReturnType ReturnType ReturnType

When overridden in a derived class, gets the result type of the XPath expression.

Methods

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

When overridden in a derived class, returns a clone of this XPathExpression.

Compile(String) Compile(String) Compile(String) Compile(String)

Compiles the XPath expression specified and returns an XPathExpression object representing the XPath expression.

Compile(String, IXmlNamespaceResolver) Compile(String, IXmlNamespaceResolver) Compile(String, IXmlNamespaceResolver) 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.

Equals(Object) Equals(Object) Equals(Object) Equals(Object)

Determines whether the specified object is equal to the current object.

(Inherited from Object)
GetHashCode() GetHashCode() GetHashCode() GetHashCode()

Serves as the default hash function.

(Inherited from Object)
GetType() GetType() GetType() GetType()

Gets the Type of the current instance.

(Inherited from Object)
MemberwiseClone() MemberwiseClone() MemberwiseClone() MemberwiseClone()

Creates a shallow copy of the current Object.

(Inherited from Object)
SetContext(IXmlNamespaceResolver) SetContext(IXmlNamespaceResolver) SetContext(IXmlNamespaceResolver) SetContext(IXmlNamespaceResolver)

When overridden in a derived class, specifies the IXmlNamespaceResolver object to use for namespace resolution.

SetContext(XmlNamespaceManager) SetContext(XmlNamespaceManager) SetContext(XmlNamespaceManager) SetContext(XmlNamespaceManager)

When overridden in a derived class, specifies the XmlNamespaceManager object to use for namespace resolution.

ToString() ToString() ToString() ToString()

Returns a string that represents the current object.

(Inherited from Object)

Applies to