Subject(3I)						    InterViews Reference Manual 					       Subject(3I)

NAME

       Subject - object with views

SYNOPSIS

       #include <InterViews/subject.h>

DESCRIPTION

       A  subject  is an object that has one or more views that it wishes to notify when it changes.  The SubjectIteractor class can be used if it
       is necessary to iterate through the views of a subject explicitly.

       Because subjects are shared, Subject is a subclass of Resource.	To allow for the possibility of multiple inheritance, in which case only a
       single copy of resource information should be maintained, Resource is a virtual base class.

PUBLIC OPERATIONS

       enum UpdateHint {
	   attaching, detaching, setting, changing
       }
	      This  type  enumerates  possible	hints when a subject is notifying a view that it has changed.  The attaching hint indicates that a
	      view has attached to the subject.  The detaching hint means that the subject is being deleted and the view  should  consider  itself
	      detached.   The  setting hint means that the subject's value has been set, though possibly to the same value as it already has.  The
	      changing hint means that the value is set to something different than it was previously.

       virtual void attach(View*)
	      Add a view to the subject's list.

       virtual void detach(View*)
	      Remove a view from the subject's list.

       virtual void notify(UpdateHint = changing)
	      Notify all the views of a subject that it has been updated.

       virtual boolean viewed_by(View*)
	      Return whether a given view is on the subject's list of views.

       virtual void Attach(Interactor*)
	      This function is equivalent to attach and is provided solely for backward compatibility.	It will be removed in a future version.

       virtual void Detach(Interactor*)
	      This function is equivalent to detach and is provided solely for backward compatibility.	It will be removed in a future version.

       virtual void Notify()
	      This function is equivalent to notify(changing) and is provided solely for backward compatibility.  It will be removed in  a  future
	      version.

       boolean IsView(Interactor*)
	      This function is equivalent to viewed_by and is provided solely for backward compatibility.  It will be removed in a future version.

SUBJECTITERATOR OPERATIONS

       A subject iterator can be used to iterate through the views in a subject.

       SubjectIterator(Subject*)
	      Create a subject iterator for the given subject.	The iterator is only valid as long as the subject exists.

       virtual void init()
	      Reset the iteration to start at the beginning of the list.  This operation is called by the constructor.

       virtual boolean more()
	      Return whether there are more views in the list.

       virtual View* cur()
	      Return the current view.

       virtual void remove()
	      Remove the current view from the list.

       virtual void next()
	      Move the iteration to the next view in the list.

SEE ALSO

       View(3I)

InterViews							   29 June 1989 						       Subject(3I)