Overriding XmlElement to Make Adding XmlAttributes Easier

May 3, 2010

When programmatically building Xml documents adding elements and their attributes can become rather repetitive and tedious. Once you create the element object you have to create separate XmlAttribute instances for each attribute of that element tag and add them to the element’s attribute collection. In many cases you will have to add the same attribute or common set of attributes to different elements throughout the document. This can be a lot easier and intuitive by overriding the XmlElement class and making the element’s properties that would be XmlAttribute instances actual instance fields (public properties) of the XmlElement object itself. So, the client end of your overridden XmlElement object will simply set the element’s attribute values just as it would the InnerText property, instead of having create XmlAttribute instances. The implementation within the overridden XmlElement will handle the construction of the XmlAttribute instances as well as adding them to its attributes collection.

By overriding XmlElement and abstracting away its attribute collection the client code can instantiate and construct XmlElements that are specific to the enterprise, much like it would normal business logic entities… and save a few lines of code along the way. See a quick comparison between the typical way of adding attributes to an Xml node and the easier way after overriding XmlElement.

The typical way – setting up an XmlAttribute object for each attribute of the XmlElement:

XmlElement employeeElement;
XmlAttribute employeeAttribute;
employeeElement = xmlDoc.CreateElement("Employee");
employeeAttribute = xml.CreateAttribute("ci:emailaddress");
employeeAttribute.Value = "sample.emp@company.com";
employeeElement.Attributes.Append(employeeAttribute);
employeeAttribute = xml.CreateAttribute("ci:phone");
employeeAttribute.Value = "123-456-7890";
employeeElement.Attributes.Append(employeeAttribute);
employeeAttribute = xml.CreateAttribute("ci:fax");
employeeAttribute.Value = "123-456-7899";
employeeElement.Attributes.Append(employeeAttribute);

The easier way – adding each attribute of the XmlElement as instance data:

ContactXmlElement employeeElement;
employeeElement = (ContactXmlElement)xmlDoc.CreateElement("Employee");
employeeElement.EmailAddress = "sample.emp@company.com";
employeeElement.Phone = "123-456-7890";
employeeElement.Fax = "123-456-7899";

In order to override XmlElement you will also have to override the CreateElement method of the XmlDocument class so you can construct objects based on your overridden implementation of XmlElement from the document object like you would normally do when creating new XmlElements.

Step 1:

Create a class that overrides XmlDocument and include an overriding implementation of the CreateElement method. Also, it is a good idea to add a public field for the attributes’ namespace if they are called from a separate namespace than the rest of the document (i.e. ci:emailAddress).

using System;
using System.Xml; 
 
namespace EdSnider.Samples
{
    public class CompanyXmlDocument : XmlDocument
    {
        public string CINamespaceURI { get; set; } 
 
        public override XmlElement CreateElement(string prefix, string localName, string namespaceURI)
        {
            if (localName == "Customer" || localName == "Employee")
            {
                return new ContactXmlElement(prefix, localName, namespaceURI, this, this.CINamespaceURI);
            }
            else
            {
                return base.CreateElement(prefix, localName, namespaceURI);
            }
        }
    }
}

Step 2:

Create a class to override XmlElement. In this implementation of XmlElement include public instance fields for each of the element’s properties that would you normally be creating XmlAttributes for. In the example below I am overriding XmlElement to make an ContactXmlElement class. In this ContactXmlElement class I am including public instance fields for Phone, Email, and Fax.

using System;
using System.Xml; 
 
namespace EdSnider.Samples
{
    public class ContactXmlElement : XmlElement
    {
        private string _phone;
        private string _emailAddress;
        private string _fax;
        private string _ciNamespaceUri; 
 
        public string Phone
        {
            get { return this._phone; }
            set { this._phone = value; base.SetAttribute("phone", this._ciNamespaceUri, value); }
        } 
 
        public string EmailAddress
        {
            get { return this._emailAddress; }
            set
            {
                this._emailAddress = value;
                base.SetAttribute("emailAddress", this._ciNamespaceUri, value);
            }
        } 
 
        public string Fax
        {
            get { return this._fax; }
            set
            {
                this._fax = value;
                base.SetAttribute("fax", this._ciNamespaceUri, value);
            }
        } 
 
        internal ContactXmlElement(string prefix, string localName, string namespaceURI, XmlDocument doc, string CINamespaceURI) : base(prefix, localName, namespaceURI, doc)
        {
            this._ciNamespaceUri = CINamespaceURI;
        }
    }
}

Step 3:

Use the overridden versions of XmlDocument and XmlElement to build a XML document within the client code:

CompanyXmlDocument xmlDoc = new CompanyXmlDocument();
xmlDoc.CINamespaceURI = "uri:edsnider:ci";
xmlDoc.LoadXml(""); // make sure you include all the appropriate namespaces within the tag – I omitted them in this sample for clarity
 
ContactXmlElement empElement = (ContactXmlElement)xmlDoc.CreateElement("Employee");
empElement.Phone = "123-456-7890";
empElement.EmailAddress = "sample.emp@company.com";
empElement.Fax = "123-456-7899";
empElement.InnerText = "Sample Employee"; 
 
xmlDoc.DocumentElement.AppendChild(empElement);

Notice that you can now set the value of the XML element attributes via the element’s object fields just like you would set the value of one of the standard XmlElement properties like InnerText.

The code in the previous snippet will create the following XML:

<company>
    <employee ci:emailaddress="sample.emp@company.com" ci:phone="123-456-7890" ci:fax="123-456-7899">
        Sample Employee
    </employee>
</company>

Ed Snider

Overriding XmlElement to Make Adding XmlAttributes Easier

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