XPathExpression-Klasse
Stellt eine typisierte Klasse bereit, die einen kompilierten XPath-Ausdruck darstellt.
Namespace: System.Xml.XPath
Assembly: System.Xml (in system.xml.dll)
Syntax
'Declaration
Public MustInherit Class XPathExpression
'Usage
Dim instance As XPathExpression
public abstract class XPathExpression
public ref class XPathExpression abstract
public abstract class XPathExpression
public abstract class XPathExpression
Hinweise
Diese Klasse wird als Ergebnis der Compile-Methode der XPathNavigator-Klasse zurückgegeben. Sie ist ein Parameter für die Methoden Evaluate, Matches, Select und SelectSingleNode der XPathNavigator-Klasse.
Hinweise für Erben Wenn Sie die XPathExpression-Klasse vererben, müssen Sie folgende Member überschreiben:
Beispiel
Im folgenden Beispiel wird veranschaulicht, wie der XPath-Rückgabetyp zum Bestimmen der Verarbeitung des XPath-Ausdrucks verwendet wird.
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", "https://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
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", "https://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;
}
}
}
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( "books.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 );
}
XPathDocument doc = new XPathDocument("books.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.
Evaluate(expr1, nav);
Evaluate(expr2, nav);
} //main
public static void Evaluate(XPathExpression expr, XPathNavigator nav)
{
switch (expr.get_ReturnType()) {
case XPathResultType.Number:
Console.WriteLine(nav.Evaluate(expr));
break;
case XPathResultType.NodeSet:
XPathNodeIterator i = nav.Select(expr);
while (i.MoveNext()) {
Console.WriteLine(i.get_Current().ToString());
}
break;
case XPathResultType.Boolean:
if (System.Convert.ToBoolean(nav.Evaluate(expr))) {
Console.WriteLine("True!");
}
break;
case XPathResultType.String:
Console.WriteLine(nav.Evaluate(expr));
break;
}
} //Evaluate
Im Beispiel wird die Datei contosoBooks.xml als Eingabe verwendet.
<bookstore xmlns="https://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>
Vererbungshierarchie
System.Object
System.Xml.XPath.XPathExpression
Threadsicherheit
Alle öffentlichen statischen (Shared in Visual Basic) Member dieses Typs sind threadsicher. Bei Instanzmembern ist die Threadsicherheit nicht gewährleistet.
Plattformen
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
.NET Framework unterstützt nicht alle Versionen sämtlicher Plattformen. Eine Liste der unterstützten Versionen finden Sie unter Systemanforderungen.
Versionsinformationen
.NET Framework
Unterstützt in: 2.0, 1.1, 1.0