XPathExpression クラスとは何？わかりやすく解説 Weblio辞書

.NET Framework クラスライブラリリファレンス

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XPathExpression クラス

コンパイル済みの XPath 式を表す、型指定されたクラスを提供します。

名前空間: System.Xml.XPath
アセンブリ: System.Xml (system.xml.dll 内)
構文

解説

このクラスは、XPathNavigator クラスの Compile メソッドの結果として返されます。これは、XPathNavigator クラスの Evaluate、Matches、Select、および SelectSingleNode 各メソッドのパラメータです。

継承時の注意 XPathExpression クラスから継承する場合は、次のメンバをオーバーライドする必要があります。

AddSort AddSort
Clone
Expression
ReturnType
SetContext
SetContext.

使用例

XPath の戻り値の型を使用して、XPath 式を確認する方法を次の例に示します。

Visual Basic

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

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;
        }
    }
}

C++

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

この例では、入力として、contosoBooks.xml というファイルを使用しています。

<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>