XmlWriter.LookupPrefix(String) 方法

定义

命名空间:

System.Xml

程序集:

System.Xml.ReaderWriter.dll

Source:

XmlWriter.cs

当在派生类中被重写时，返回在当前命名空间范围中为该命名空间 URI 定义的最近的前缀。

public:
 abstract System::String ^ LookupPrefix(System::String ^ ns);

public abstract string? LookupPrefix (string ns);

abstract member LookupPrefix : string -> string

Public MustOverride Function LookupPrefix (ns As String) As String

参数

ns

String

要查找其前缀的命名空间 URI。

返回

String

匹配的前缀；如果当前范围内未找到匹配的命名空间 URI，则为 null。

例外

ArgumentException

ns 为 null 或 String.Empty。

InvalidOperationException

在上一次异步操作完成之前调用了 XmlWriter 方法。 在此情况下，会引发 InvalidOperationException 并显示消息“异步操作已在进行中。”

示例

以下示例写出一本书。

#using <System.Xml.dll>

using namespace System;
using namespace System::IO;
using namespace System::Xml;
public ref class Sample
{
private:
   static String^ m_Document = L"sampledata.xml";

public:
   static void Main()
   {
      XmlWriter^ writer = nullptr;
      try
      {
         XmlWriterSettings^ settings = gcnew XmlWriterSettings;
         settings->Indent = true;
         writer = XmlWriter::Create( m_Document,settings );
         writer->WriteComment( L"sample XML fragment" );
         
         // Write an element (this one is the root).
         writer->WriteStartElement( L"book" );
         
         // Write the namespace declaration.
         writer->WriteAttributeString( L"xmlns", L"bk", nullptr, L"urn:samples" );
         
         // Write the genre attribute.
         writer->WriteAttributeString( L"genre", L"novel" );
         
         // Write the title.
         writer->WriteStartElement( L"title" );
         writer->WriteString( L"The Handmaid's Tale" );
         writer->WriteEndElement();
         
         // Write the price.
         writer->WriteElementString( L"price", L"19.95" );
         
         // Lookup the prefix and write the ISBN element.
         String^ prefix = writer->LookupPrefix( L"urn:samples" );
         writer->WriteStartElement( prefix, L"ISBN", L"urn:samples" );
         writer->WriteString( L"1-861003-78" );
         writer->WriteEndElement();
         
         // Write the style element (shows a different way to handle prefixes).
         writer->WriteElementString( L"style", L"urn:samples", L"hardcover" );
         
         // Write the close tag for the root element.
         writer->WriteEndElement();
         
         // Write the XML to file and close the writer.
         writer->Flush();
         writer->Close();
      }
      finally
      {
         if ( writer != nullptr )
                  writer->Close();
      }

   }

};

void main()
{
   Sample::Main();
}

using System;
using System.IO;
using System.Xml;

 public class Sample
 {
   private const string m_Document = "sampledata.xml";

   public static void Main() {

      XmlWriter writer = null;

      try {

        XmlWriterSettings settings = new XmlWriterSettings();
        settings.Indent = true;
        writer = XmlWriter.Create (m_Document, settings);

        writer.WriteComment("sample XML fragment");

        // Write an element (this one is the root).
        writer.WriteStartElement("book");

        // Write the namespace declaration.
        writer.WriteAttributeString("xmlns", "bk", null, "urn:samples");

        // Write the genre attribute.
        writer.WriteAttributeString("genre", "novel");

        // Write the title.
        writer.WriteStartElement("title");
        writer.WriteString("The Handmaid's Tale");
        writer.WriteEndElement();

        // Write the price.
        writer.WriteElementString("price", "19.95");

        // Lookup the prefix and write the ISBN element.
        string prefix = writer.LookupPrefix("urn:samples");
        writer.WriteStartElement(prefix, "ISBN", "urn:samples");
        writer.WriteString("1-861003-78");
        writer.WriteEndElement();

        // Write the style element (shows a different way to handle prefixes).
        writer.WriteElementString("style", "urn:samples", "hardcover");

        // Write the close tag for the root element.
        writer.WriteEndElement();

        // Write the XML to file and close the writer.
        writer.Flush();
        writer.Close();
      }

      finally {
        if (writer != null)
           writer.Close();
     }
   }
 }

Option Strict
Option Explicit

Imports System.IO
Imports System.Xml

Public Class Sample
    Private Shared m_Document As String = "sampledata.xml"
    
    Public Shared Sub Main()
        Dim writer As XmlWriter = Nothing
        
      Try

        Dim settings As XmlWriterSettings = new XmlWriterSettings()
        settings.Indent = true
        writer = XmlWriter.Create (m_Document, settings)
            
        writer.WriteComment("sample XML fragment")
            
        ' Write an element (this one is the root).
        writer.WriteStartElement("book")
            
        ' Write the namespace declaration.
        writer.WriteAttributeString("xmlns", "bk", Nothing, "urn:samples")
            
        ' Write the genre attribute.
        writer.WriteAttributeString("genre", "novel")
            
        ' Write the title.
        writer.WriteStartElement("title")
        writer.WriteString("The Handmaid's Tale")
        writer.WriteEndElement()
            
        ' Write the price.
        writer.WriteElementString("price", "19.95")
            
        ' Lookup the prefix and write the ISBN element.
        Dim prefix As String = writer.LookupPrefix("urn:samples")
        writer.WriteStartElement(prefix, "ISBN", "urn:samples")
        writer.WriteString("1-861003-78")
        writer.WriteEndElement()
            
        ' Write the style element (shows a different way to handle prefixes).
        writer.WriteElementString("style", "urn:samples", "hardcover")
            
        ' Write the close tag for the root element.
        writer.WriteEndElement()
            
        ' Write the XML to file and close the writer.
        writer.Flush()
        writer.Close()
        
        Finally
            If Not (writer Is Nothing) Then
                writer.Close()
            End If
        End Try

    End Sub
End Class