This documentation is archived and is not being maintained.

XmlWriter.LookupPrefix Method

When overridden in a derived class, returns the closest prefix defined in the current namespace scope for the namespace URI.

Namespace: System.Xml
Assembly: System.Xml (in system.xml.dll)

public abstract string LookupPrefix (
	string ns
public abstract String LookupPrefix (
	String ns
public abstract function LookupPrefix (
	ns : String
) : String
Not applicable.



The namespace URI whose prefix you want to find.

Return Value

The matching prefix or a null reference (Nothing in Visual Basic) if no matching namespace URI is found in the current scope.

Exception typeCondition


ns is either a null reference (Nothing in Visual Basic) or String.Empty.

The following example writes out a book.

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).
        // Write the namespace declaration.
        writer.WriteAttributeString("xmlns", "bk", null, "urn:samples");
        // Write the genre attribute.
        writer.WriteAttributeString("genre", "novel");
        // Write the title.
        writer.WriteString("The Handmaid's Tale");
        // 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");

        // 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.
        // Write the XML to file and close the writer.

      finally {
        if (writer != null)

Windows 98, Windows Server 2000 SP4, Windows CE, Windows Millennium Edition, Windows Mobile for Pocket PC, Windows Mobile for Smartphone, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

The Microsoft .NET Framework 3.0 is supported on Windows Vista, Microsoft Windows XP SP2, and Windows Server 2003 SP1.

.NET Framework

Supported in: 3.0, 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 2.0, 1.0

XNA Framework

Supported in: 1.0