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Unordered Node Retrieval by Name or Index 

The XmlNamedNodeMap is described in the World Wide Web Consortium (W3C) specification as the NamedNodeMap and is required to handle an unordered set of nodes with the ability to reference nodes by their name or index. The only way you have access to an XmlNamedNodeMap is when an XmlNamedNodeMap is returned through a method or property. There are three methods or properties that return an XmlNamedNodeMap:

  • XmlElement.Attributes

  • XmlDocumentType.Entities

  • XmlDocumentType.Notations

For example, the XmlDocumentType.Entities property gets the collection of XmlEntity nodes declared in the document type declaration. This collection is returned as an XmlNamedNodeMap, and you can iterate through the collection with the use of the Count property and display entity information. For an example of iterating through an XmlNamedNodeMap, see XmlDocumentType.Entities Property.

The XmlAttributeCollection is derived from XmlNamedNodeMap and only attributes are modifiable, while notations and entities are read-only. Using the XmlNamedNodeMap for the attributes, you can get nodes for those attributes based on their XML names. This provides an easy method for manipulating the collection of attributes on an element node. This can be contrasted directly with XmlNodeList, which also implements the IEnumerable interface, but with an index accessor rather than a string. The RemoveNamedItem and SetNamedItem methods are only used against an XmlAttributeCollection. Adding or removing from an attribute collection, whether using the AttributeCollection or the XmlNamedNodeMap implementation, modifies the attribute collection on the element. The following code example shows how to move an attribute and create a new attribute.

using System;
using System.Xml;
class test {
    public static void Main() {
        XmlDocument doc = new XmlDocument();
        doc.LoadXml( "<root> <child1 attr1='val1' attr2='val2'> text1 </child1> <child2 attr3='val3'> text2 </child2> </root> " );

        // Get the attributes of node "child2"
        XmlAttributeCollection ac = doc.DocumentElement.ChildNodes[1].Attributes;

        // Print out the number of attributes and their names.
        Console.WriteLine( "Number of Attributes: "+ac.Count );
        for( int i = 0; i < ac.Count; i++ )
            Console.WriteLine( (i+1) + ".  Attribute Name: '" +ac[i].Name+ "'  Attribute Value:  '"+ ac[i].Value +"'" ); 

        // Get the 'attr1' from child1.
        XmlAttribute attr = doc.DocumentElement.ChildNodes[0].Attributes[0];

        // Add this attribute to the attributecollection "ac".
        ac.SetNamedItem( attr );

        // 'attr1' will be removed from 'child1' and added to 'child2'.
        // Print out the number of attributes and their names.
        Console.WriteLine( "Number of Attributes: "+ac.Count );        
        for( int i = 0; i < ac.Count; i++ )
            Console.WriteLine( (i+1) + ".  Attribute Name: '" +ac[i].Name+ "'  Attribute Value:  '"+ ac[i].Value +"'" ); 

        // Create a new attribute and add to the collection.
        XmlAttribute attr2 = doc.CreateAttribute( "attr4" );
        attr2.Value = "val4";
        ac.SetNamedItem( attr2 );

        // Print out the number of attributes and their names.
        Console.WriteLine( "Number of Attributes: "+ac.Count );        
        for( int i = 0; i < ac.Count; i++ )
            Console.WriteLine( (i+1) + ".  Attribute Name: '" +ac[i].Name+ "'  Attribute Value:  '"+ ac[i].Value +"'" );         
       
    }
}

To see an additional code example which shows an attribute being removed from an AttributeCollection, see XmlNamedNodeMap.RemoveNamedItem Method. For more information on the methods and properties, see XmlNamedNodeMap Members.

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