NAME¶
classes - unique identifiers for catalog-managed objects and component views
SYNOPSIS¶
#include <Unidraw/classes.h>
DESCRIPTION¶
Classes for catalog-managed objects, including components, commands, tools,
state variables, and transfer functions, must be associated with
mutually-unique class identifiers that can be written onto disk. This allows a
creator object to call the appropriate constructor as part of recreating an
object from disk.
Also, there must be a mechanism for creating an appropriate view given a
subject; that is, there must be an association between a subject class and
allowable view classes for that subject. This association is established by
defining class identifiers for component views. These identifiers are formed
by concatenating the identifier for a given component subject class with an
identifier that specifies a ``view category.'' For example, the class
identifier for the PostScript external view of a line component is the
concatenation of the identifier for the line component subject class and
POSTSCRIPT_VIEW identifier, which specifies the category of external views for
generating PostScript. This makes it possible to create an instance of the
appropriate PostScript external view subclass given a line component subject.
The class identifiers for the Unidraw base and predefined derived classes are
specified in the
classes.h include file. Applications that define new
catalog-managed objects or component views should define unique class
identifiers in a similar manner. Class identifiers for catalog-managed objects
are simply integers with mnemonic macro definitions, usually the class name in
all-uppercase. For example, the identifier for the LineComp component subject
class is
#define LINE_COMP 9030
View class identifiers are specified using the Combine macro, which takes as its
first argument the macro definition of the corresponding component subject
identifier; its second argument is an identifier for the view category. The
Combine macro itself is then defined with a mnemonic name. For example, the
identifier for the PostScript external view class PSLine (which generates
PostScript for the line component subject) is defined as
#define PS_LINE Combine(LINE_COMP, POSTSCRIPT_VIEW)
where the POSTSCRIPT_VIEW view category identifier is defined as
#define POSTSCRIPT_VIEW 9103
N.B.:
All class identifiers in a given application must be unique.
SEE ALSO¶
Catalog(3U), Creator(3U)