VWLib REFERENCE MANUAL

NAME

vwSubject -

An abstract base class for vwLib. vwSubject is the subject component of the Observer Pattern in this library. The abstract vwWidget class, and thus all widgets descend from vwSubject.

HEADER FILE

#include <dependents.h>

PUBLIC METHOD SUMMARY

virtual vwSubject::~vwSubject (

void);

void vwSubject::attach (

vwObserver * concreteObserver);

void vwSubject::detach (

vwObserver * concreteObserver);

inline void * vwSubject::getSubjectData (

void);

inline unsigned long vwSubject::getID (

void);

PROTECTED METHOD SUMMARY

vwSubject::vwSubject (

vwMediator *concreteMediator);

virtual void vwSubect::notify (

void);

inline void vwSubject::setSubjectData (

void * data);

CLASS DESCRIPTION

vwSubject is the abstract subject class of the Observer Pattern on which this Liberia is based. In congruence with a Mediator Pattern concrete mediator who's abstract class is vwMediator, vwSubject facilitates event propagation from its descendent widgets to concrete observers.

METHOD DESCRIPTIONS

   vwSubject() [Protected]

vwSubect (

vwMediator *concreteMediator);

Construct a vwSubject.

*concreteMediator specifies a pointer to the concrete mediator of the Mediator Pattern. Normally there is only one concrete mediator in an application. It is a public derivative of the abstract vwMediator class.

   ~vwSubject()

virtual ~vwSubject (

void);

Destruct an instance. The destructor removes its reference from the concrete mediator's subject list.

   attach()

void attach (

vwObserver * concreteObserver);

Attach a concrete observer to this subject. While an observer is attached, each time this subject's  notify() method is called, the observer's vwObserver::update() method will be called once. The concrete mediator will maintain one list for each subject. There will be no more than one reference to a particular observer maintained for any given subject.

*concreteObserver specifies a  pointer to a public derivative of the abstract vwObserver.

   detach()

void detach (

vwObserver * concreteObserver);

Remove an observer from the subjects list of observers. vwObserver::update() will no longer be called when this subjects notify() method is executed.

*concreteObserver specifies a pointer to a publicly derived  instance of the abstract vwObserver.

    getSubjectData()

inline void * getSubjectData (

void);

Returns a pointer to a subject's data. If not set, returns NULL.

   getID()

virtual unsigned long getID (

void);

Get a subject's ID number. A subject's unique ID value can be used to identify it.

   notify() [Protected]

void notify (

void);

Generate an event. notify() generates a call to vwObserver::update() of all concrete observers that are attached to the subject. This is done at a low level through the concrete vwMediator which maintains subject - observer lists in a Mediator Pattern that handles all bookkeeping for the Observer Pattern.

  setSubjectData() [Protected]

inline void setSubjectData (

void * data);

Set a pointer to data that will be passed to vwObserver::update() of all observers attached to this subject.

*data specifies a void pointer to some memory address. The constructors of certain widgets (e.g., vwSlider) call setSubjectData() with the parameter *data being a pointer to their data value.

SEE ALSO

vwMediator, vwObserver