To make use of the observer, it is best to implement a custom page class. The custom page class is a class that inherits from System.Web.UI.Page and works like regular inheritance does. The reason to implement a custom page class is because of the specialized nature of how this will work. It is possible to not have to use a custom page class; however, for unit testing purposes it makes it helpful to do so.

One of the approaches to implementing the observer pattern is to have the page act as the subject. It is the one that controls certain interactions and notifies its children that an update needs made. The children are most likely user controls because the means to update will require the use of an interface. Each user control would implement from a custom user control base class, similar to how the custom page class works.