XmlWriter.WriteAttributeString Method (String, String, String)


When overridden in a derived class, writes an attribute with the specified local name, namespace URI, and value.

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

Public Sub WriteAttributeString (
	localName As String,
	ns As String,
	value As String


Type: System.String

The local name of the attribute.

Type: System.String

The namespace URI to associate with the attribute.

Type: System.String

The value of the attribute.

Exception Condition

The state of writer is not WriteState.Element or writer is closed.


The xml:space or xml:lang attribute value is invalid.


An XmlWriter method was called before a previous asynchronous operation finished. In this case, InvalidOperationException is thrown with the message “An asynchronous operation is already in progress.”

This method writes out the attribute with a user defined namespace prefix and associates it with the given namespace. If localName is "xmlns" then this method also treats this as a namespace declaration. In this case, the ns argument can be null.

WriteAttributeString does the following:

  • If the attribute value includes double or single quotes, they are replaced with " and ' respectively.

  • If writing an xml:space attribute, the writer verifies the attribute value is valid. (Valid values are preserve or default.)

  • If writing an xml:lang attribute, the writer does not verify that the attribute value is valid according to the W3C XML 1.0 recommendation.

For the asynchronous version of this method, see WriteAttributeStringAsync.

The following example uses the WriteAttributeString method to write a namespace declaration.

Imports System
Imports System.IO
Imports System.Xml

Public Class Sample 

  Public Shared Sub Main() 

     Dim writer As XmlWriter = Nothing

     writer = XmlWriter.Create("sampledata.xml")

     ' Write the root element.

     ' Write the xmlns:bk="urn:book" namespace declaration.
     writer.WriteAttributeString("xmlns","bk", Nothing,"urn:book")

     ' Write the bk:ISBN="1-800-925" attribute.
     writer.WriteAttributeString("ISBN", "urn:book", "1-800-925")

     writer.WriteElementString("price", "19.95")

     ' Write the close tag for the root element.

     ' Write the XML to file and close the writer.

  End Sub
End Class

Universal Windows Platform
Available since 8
.NET Framework
Available since 1.1
Portable Class Library
Supported in: portable .NET platforms
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1
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