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XPathExpression 類別

定義

提供代表已編譯 XPath 運算式的具類型類別。

public ref class XPathExpression abstract
public abstract class XPathExpression
type XPathExpression = class
Public MustInherit Class XPathExpression
繼承
XPathExpression

範例

下列範例示範如何使用 XPath 傳回類型來判斷如何處理 XPath 運算式。

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.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

該範例採用 contosoBooks.xml 檔案做為輸入。

<?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>  

備註

這個類別會以 類別的 XPathNavigator 方法結果 Compile 傳回。 它是 類別之 EvaluateMatchesSelectSelectSingleNode 方法的參數 XPathNavigator

給實施者的注意事項

當您繼承自 類別時 XPathExpression ,必須覆寫下列成員:

屬性

Expression

在衍生類別中覆寫時,取得 XPathExpressionstring 表示。

ReturnType

在衍生類別中覆寫時,取得 XPath 運算式的結果類型。

方法

AddSort(Object, IComparer)

在衍生類別中覆寫時,根據指定的 IComparer 物件,對 XPath 運算式所選取的節點進行排序。

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

在衍生類別中進行覆寫時,根據提供的參數來排序 XPath 運算式所選取的節點。

Clone()

在衍生類別中覆寫時,傳回這個 XPathExpression 的複製。

Compile(String)

編譯指定的 XPath 運算式,並傳回代表 XPath運算式的 XPathExpression 物件。

Compile(String, IXmlNamespaceResolver)

以為命名空間解析指定的 IXmlNamespaceResolver 物件,編譯指定的 XPath 運算式,並傳回表示 XPath 運算式的 XPathExpression 物件。

Equals(Object)

判斷指定的物件是否等於目前的物件。

(繼承來源 Object)
GetHashCode()

做為預設雜湊函式。

(繼承來源 Object)
GetType()

取得目前執行個體的 Type

(繼承來源 Object)
MemberwiseClone()

建立目前 Object 的淺層複製。

(繼承來源 Object)
SetContext(IXmlNamespaceResolver)

在衍生類別中覆寫時,指定 IXmlNamespaceResolver 物件用於命名空間解析。

SetContext(XmlNamespaceManager)

在衍生類別中覆寫時,指定 XmlNamespaceManager 物件用於命名空間解析。

ToString()

傳回代表目前物件的字串。

(繼承來源 Object)

適用於