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Create new attributes for elements in the DOM

  • Article

Creating new attributes is different than creating other node types, because attributes are not nodes. They are properties of an element node and are contained in an XmlAttributeCollection associated with the element. There are multiple ways to create an attribute and attach it to an element:

  • Get the element node and use SetAttribute to add an attribute to the attribute collection of that element.

  • Create an XmlAttribute node using the CreateAttribute method, get the element node, then use SetAttributeNode to add the node to the attribute collection of that element.

The following example shows how to add an attribute to an element using the SetAttribute method:

Imports System.IO
Imports System.Xml

Public Class Sample

    Public Shared Sub Main()

        Dim doc As New XmlDocument()
        doc.LoadXml("<book xmlns:bk='urn:samples' bk:ISBN='1-861001-57-5'>" & _
                    "<title>Pride And Prejudice</title>" & _
                    "</book>")
        Dim root As XmlElement = doc.DocumentElement

        ' Add a new attribute.
        root.SetAttribute("genre", "urn:samples", "novel")

        Console.WriteLine("Display the modified XML...")
        Console.WriteLine(doc.InnerXml)
    End Sub
End Class

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

public class Sample
{
    public static void Main()
    {
        var doc = new XmlDocument();
        doc.LoadXml("<book xmlns:bk='urn:samples' bk:ISBN='1-861001-57-5'>" +
                    "<title>Pride And Prejudice</title>" +
                    "</book>");
        XmlElement root = doc.DocumentElement;

        // Add a new attribute.
        root.SetAttribute("genre", "urn:samples", "novel");

        Console.WriteLine("Display the modified XML...");
        Console.WriteLine(doc.InnerXml);
    }
}

The following example shows how to create a new attribute using the CreateAttribute method. The attribute is then added to the attribute collection of the book element using the SetAttributeNode method.

Given the following XML:

<book genre='novel' ISBN='1-861001-57-5'>
<title>Pride And Prejudice</title>
</book>

Create a new attribute and give it a value:

Dim attr As XmlAttribute = doc.CreateAttribute("publisher")
attr.Value = "WorldWide Publishing"

XmlAttribute attr = doc.CreateAttribute("publisher");
attr.Value = "WorldWide Publishing";

Attach the attribute to the element:

doc.DocumentElement.SetAttributeNode(attr)

doc.DocumentElement.SetAttributeNode(attr);

Output

<book genre="novel" ISBN="1-861001-57-5" publisher="WorldWide Publishing">
<title>Pride And Prejudice</title>
</book>

The full code sample can be found at CreateAttribute.

If you created an XmlNamedNodeMap of attributes, you can add an attribute by name using the SetNamedItem method. For more information, see Node Collections in NamedNodeMaps and NodeLists.

Default attributes

If you create an element that is declared to have a default attribute, then a new default attribute with its default value is created by the XML Document Object Model (DOM) and attached to the element. The child nodes of the default attribute are also created at this time.

Attribute child nodes

The value of an attribute node becomes its child nodes. There are only two types of valid child nodes: XmlText nodes and XmlEntityReference nodes. These are child nodes in the sense that methods such as FirstChild and LastChild process them as child nodes. This distinction of an attribute having child nodes is important when trying to remove attributes or attribute child nodes. For more information, see Removing Attributes from an Element Node in the DOM.

See also