namespace MVC

　{

　public class Book

　{

　// declare a delegate for the bookpricechanged event

　public delegate void BookPriceChangedHandler(objectsender,

　BookPriceChangedEventArgs e);

　// declare the bookpricechanged event using the bookpricechangeddelegate

　public event BookPriceChangedHandlerBookPriceChanged;

　// instance variable for book price

　object _bookPrice;

　// property for book price

　public object BookPrice

　{

　set

　{

　// set the instance variable

　_bookPrice=value;

　// the price changed so fire the event!

　OnBookPriceChanged();

　}

　}

　// method to fire price canged event delegate with proper name

　// this is the method our observers should be implenting!

　protected void OnBookPriceChanged()

　{

　BookPriceChanged(this, new BookPriceChangedEventArgs(_bookPrice));

　}

　}

　}