December, 2008

  • Eric White's Blog

    Convert XElement to XmlNode (and Convert XmlNode to XElement)

    • 11 Comments

    Sometimes you want to convert an XmlNode to an XElement and back again.  Some programming libraries define methods that take XmlNode objects as parameters.  These libraries also may contain properties and methods that return XmlNode objects.  However, it is more convenient to work with LINQ to XML instead of the classes in System.Xml (XmlDocument, XmlNode, etc.)  This post presents a bit of code to do these conversions.

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    Blog TOC
    (Update March 5, 2009 - I've written a blog post that shows how to convert from XDocument to XmlDocument (and vice versa).  The code presented in that post is a superset of the code presented in this code.)

    As an example of where you need these methods, you can do a lot with SharePoint using web services.  The proxy classes that wsdl.exe creates contain methods that use classes in System.Xml.

    It is convenient to write these conversions as extension methods.  When converting to and from classes in System.Xml, the code reads much better when you tack an extension method on the end instead of surrounding the expression with a method call.  The following code shows how to call the GetListItems method of the Lists web service using the GetXmlNode and GetXElement extension methods:

    XElement queryOptions = new XElement("QueryOptions",
        new XElement("Folder", "Open XML Documents"),
        new XElement("ViewAttributes", new XAttribute("Scope", "Recursive"))
    );

    XElement viewFields = new XElement("ViewFields",
        new XElement("FieldRef", new XAttribute("Name", "GUID")),
        new XElement("FieldRef", new XAttribute("Name", "ContentType")),
        new XElement("FieldRef", new XAttribute("Name", "BaseName")),
        new XElement("FieldRef", new XAttribute("Name", "Modified")),
        new XElement("FieldRef", new XAttribute("Name", "EncodedAbsUrl"))
    );

    XElement listContent = wsList
        .GetListItems(documentLibraryGUID,
                      null, null, viewFields.GetXmlNode(),
                      null, queryOptions.GetXmlNode(), webId)
        .GetXElement();

    To create an XmlNode from an XElement, you create an XmlReader using the XNode.CreateReader method, create an XmlDocument, and load the document using the XmlReader.  XmlDocument inherits XmlNode.

    To create an XElement from an XmlNode, you create an XDocument, create an XmlWriter using the XContainer.CreateWriter method, write the XmlNode to the XDocument, and return the root element of the XDocument.

    The following example contains the extension methods and some code that shows their use:

    using System;
    using System.Collections.Generic;
    using System.Linq;
    using System.Xml;
    using System.Xml.Linq;

    public static class MyExtensions
    {
        public static XElement GetXElement(this XmlNode node)
        {
            XDocument xDoc = new XDocument();
            using (XmlWriter xmlWriter = xDoc.CreateWriter())
                node.WriteTo(xmlWriter);
            return xDoc.Root;
        }

        public static XmlNode GetXmlNode(this XElement element)
        {
            using (XmlReader xmlReader = element.CreateReader())
            {
                XmlDocument xmlDoc = new XmlDocument();
                xmlDoc.Load(xmlReader);
                return xmlDoc;
            }
        }
    }

    class Program
    {
        static void Main(string[] args)
        {
            XElement e = new XElement("Root",
                new XElement("Child",
                    new XAttribute("Att", "1")
                )
            );

            XmlNode xmlNode = e.GetXmlNode();
            Console.WriteLine(xmlNode.OuterXml);

            XElement newElement = xmlNode.GetXElement();
            Console.WriteLine(newElement);
        }
    }

    Code is attached.

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