Bearbeiten

Freigeben über

XPathExpression.Compile Method

  • Reference

Definition

Namespace:
System.Xml.XPath
Assembly:
System.Xml.ReaderWriter.dll
Assembly:
System.Xml.XPath.dll
Assembly:
System.Xml.dll
Assembly:
netstandard.dll

Compiles the XPath expression specified and returns an XPathExpression object that represents the XPath expression.

Overloads

Compile(String)

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

Source:
XPathExpr.cs
Source:
XPathExpr.cs
Source:
XPathExpr.cs

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

public:
 static System::Xml::XPath::XPathExpression ^ Compile(System::String ^ xpath);
public static System.Xml.XPath.XPathExpression Compile (string xpath);
static member Compile : string -> System.Xml.XPath.XPathExpression
Public Shared Function Compile (xpath As String) As XPathExpression

Parameters

xpath
String

An XPath expression.

Returns

XPathExpression

An XPathExpression object.

Exceptions

ArgumentException

The XPath expression parameter is not a valid XPath expression.

XPathException

The XPath expression is not valid.

Examples

The following example shows how to use the XPath return type to determine how to process the XPath expression. The example uses the Compile method to return the new XPathExpression objects.

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

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

An XPath expression is evaluated to yield one of the following result types.

Note

If a user-defined function with an invalid number of arguments (or an unimplemented user-defined function) is specified in the XPath expression, an exception occurs only at run time. User-defined functions are not checked at compile time and exceptions that result from user-defined functions occur only if execution evaluates the expression.

See also

Applies to

Compile(String, IXmlNamespaceResolver)

Source:
XPathExpr.cs
Source:
XPathExpr.cs
Source:
XPathExpr.cs

Compiles the specified XPath expression, with the IXmlNamespaceResolver object specified for namespace resolution, and returns an XPathExpression object that represents the XPath expression.

public:
 static System::Xml::XPath::XPathExpression ^ Compile(System::String ^ xpath, System::Xml::IXmlNamespaceResolver ^ nsResolver);
public static System.Xml.XPath.XPathExpression Compile (string xpath, System.Xml.IXmlNamespaceResolver? nsResolver);
public static System.Xml.XPath.XPathExpression Compile (string xpath, System.Xml.IXmlNamespaceResolver nsResolver);
static member Compile : string * System.Xml.IXmlNamespaceResolver -> System.Xml.XPath.XPathExpression
Public Shared Function Compile (xpath As String, nsResolver As IXmlNamespaceResolver) As XPathExpression

Parameters

xpath
String

An XPath expression.

nsResolver
IXmlNamespaceResolver

An object that implements the IXmlNamespaceResolver interface for namespace resolution.

Returns

XPathExpression

An XPathExpression object.

Exceptions

ArgumentException

The XPath expression parameter is not a valid XPath expression.

XPathException

The XPath expression is not valid.

Remarks

An XPath expression is evaluated to yield one of the following result types.

Note

If a user-defined function with an invalid number of arguments (or an unimplemented user-defined function) is specified in the XPath expression, an exception occurs only at run-time. User-defined functions are not checked at compile time and exceptions resulting from user-defined functions occur only if execution evaluates the expression.

Note

It is not possible to compile a XPathExpression with a custom context in one step by passing an XsltContext, which implements IXmlNamespaceResolver, as an argument to this method. To use a XPathExpression with a custom context, you must call the SetContext method after compiling the expression.

See also

Applies to