Business objects and controls do not have a generic way to provide notification when a property changes.  The current convention is to provide a property changed event for each property (e.g. "PropertyName"Changed event handler).  For business object types or controls with many properties, this can lead to a cumbersome object model.  INotifyPropertyChanged provides a simpler, interface based approach to providing property change notification.

Sample: Simple Binding with INotifyPropertyChanged Change Notification (VS 2005) (VS Project: PropertyChangeNotification)

using System.ComponentModel;

public class CurrentTime : INotifyPropertyChanged
{
    System.Windows.Forms.Timer      _timer;

    public CurrentTime()
    {
        /***************************************************************
        * Use a timer to keep track of the current time
        ***************************************************************/
        
        _timer = new System.Windows.Forms.Timer();

        /***************************************************************
        * Update the time every second
        ***************************************************************/

        _timer.Interval = 1000;
        _timer.Tick += delegate { this.Now = DateTime.Now; };
        _timer.Start();
    }

    /*******************************************************************
    * Use a timer to keep track of the current time
    *******************************************************************/

    private DateTime _now = DateTime.Now;

    /*******************************************************************
    * Property Change Notification fired – bound UI elements will
    * update when this property changed
    *
    * This uses INotifyPropertyChanged
    *******************************************************************/

    public DateTime Now
    {
        get { return _now; }
        private set
        {
            if (_now != value)
            {
                _now = value;
                OnPropertyChanged("Now");
        }
        }
    }

    /*******************************************************************
    * Provide the INotifyPropertyChanged.PropertyChanged event
    *******************************************************************/

    public event PropertyChangedEventHandler PropertyChanged;

  protected virtual void OnPropertyChanged(string propertyName)
    {
    OnPropertyChanged(new PropertyChangedEventArgs(propertyName));
    }

    protected virtual void OnPropertyChanged(PropertyChangedEventArgs e)
    {
     if (null != PropertyChanged)
    {
     PropertyChanged(this, e);
     }
    }
}