INotifyPropertyChanged and Beyond - Part I

using System;
using System.ComponentModel;

namespace NotifyTest {
	/// <summary>
	/// This class extends <see cref="T:PropertyChangedEventArgs"/> and
	/// allows for storing the old and new values of the changed property.
	/// </summary>
	public class PropertyNotificationEventArgs : PropertyChangedEventArgs {
		#region Constructors

		/// <summary>
		/// Initializes a new instance of the
		/// <see cref="PropertyNotificationEventArgs"/> class.
		/// </summary>
		/// <param name="propertyName">
		/// The name of the property that is associated with this
		/// notification.
		/// </param>
		public PropertyNotificationEventArgs(String propertyName)
			: this(propertyName, null, null) {
			// No-op
		}

		/// <summary>
		/// Initializes a new instance of the
		/// <see cref="PropertyNotificationEventArgs"/> class.
		/// </summary>
		/// <param name="propertyName">
		/// The name of the property that is associated with this
		/// notification.
		/// </param>
		/// <param name="oldValue">The old value.</param>
		/// <param name="newValue">The new value.</param>
		public PropertyNotificationEventArgs(String propertyName,
			Object oldValue, Object newValue)
			: base(propertyName) {
			this.oldValue = oldValue;
			this.newValue = newValue;
		}

		#endregion // Constructors

		#region Properties

		/// <summary>
		/// Holds the new value of the property.
		/// </summary>
		private Object newValue;

		/// <summary>
		/// Gets the new value of the property.
		/// </summary>
		/// <value>The new value.</value>
		public Object NewValue {
			get {
				return this.newValue;
			}
		}

		/// <summary>
		/// Holds the old value of the property.
		/// </summary>
		private Object oldValue;

		/// <summary>
		/// Gets the old value of the property.
		/// </summary>
		/// <value>The old value.</value>
		public Object OldValue {
			get {
				return this.oldValue;
			}
		}

		#endregion // Properties
	}
}