Defines a one-to-many dependency between objects so that when one object changes
state, all of its dependents are notified and updated automatically.
Category:
Behavioral
UML Diagram:
Description of the Demonstration:
The WeatherData class, a sub-class of Subject, maintains a vector of
pointers to instances of sub-classes of Observer. The subclasses are
PDADisplay, TVDisplay, and GPSDisplay. At startup in main() instances
of each subclass of Observer are created and passed to the instance of
WeatherData::registerObserver. The demonstration loop then runs for
15 seconds. Each second the instance of WeatherData is told to collect
all of its weather information then a call is made to WeatherData::notifyObservers.
The WeatherData object then calls Observer::update on each of the Observers it has
registered. Each Observer can then make calls back to WeatherData to get
the data they need to display. At any time an Observer can call WeatherData::removeObserver
to unsubscribe from the data feed or call WeatherData::registerObserver to
resubscribe to the data feed.
Code:
Click here to download a
zip file containing all the source files and an executable of the
Demonstration. See the _ReadMe.txt file in the zip.
