Constraint initialize() Constraint initialize()
Name
Constraint initialize - Constraint class method to initialize a child object or widget's constraint record.
Synopsis
typedef void (*XtInitProc)(Widget, Widget, ArgList, Cardinal *);
Widget request;
Widget init;
ArgList args;
Cardinal *num_args;
Inputs
request Specifies the newly created child widget or object instance with its constraint record resource values set as requested by the
argument list, the resource database, and the constraint defaults.
init Specifies the same widget or object with its constraint record fields as modified by any superclass Constraint initialize() meth-
ods.
args Specifies the argument list that was passed to XtCreateWidget().
num_args Specifies the number of entries in the argument list.
Description
The Constraint initialize() method is registered on the initialize field of the Constraint class part structure, and is called by XtCre-
ateWidget() when a child of the constraint widget is created. The Constraint initialize() method performs the same sort of initializations
on the constraint record of a widget that the normal (Object, RectObj, or Core) initialize() method performs on the widget instance struc-
ture.
The request and init arguments specify the child widget that is being created. The constraints field of the request widget points to a
copy of the constraint record as it was after all of the constraint resources were initialized from the argument list, the resource data-
base, or the resource list defaults. The constraints field of the init widget points to the actual constraints record of the widget, and
has been further initialized by the Constraint initialize() method of any Constraint superclasses of the parent widget. All modifications
should be made to the init constraints record; the request argument exists so that the widget class can determine which field of the con-
straints record have been modified by superclass Constraint initialize() methods.
The Constraint initialize() method is chained in superclass-to-subclass order, and cannot be inherited. If nothing in the constraint
structure needs initialization, the Constraint class part initialize field should be NULL.
The args and num_args arguments were added to this method in Release 4.
See initialize(4) for an explanation of the things that an initialize procedure should do. See XtCreateWidget(1) for full details of the
widget creation process.
Example
The following procedure is the Constraint initialize() method, slightly modified, of the Athena Form widget class. Note how it obtains the
constraint record and the parent form widget from the supplied child widget. Note also that it provides "dynamic defaults" for two of its
constraint resources: if dx or dy is equal to some default value (i.e., if it was not explicitly specified), then it will be replaced by
the value of the XtNdefaultSpacing resource from the Form widget itself.
Note that this procedure (and most other initialize() procedures in existence) has named its init argument new. "new" is a reserved word
in C++, and your programs will be more portable if you avoid using it in your C code.
/* ARGSUSED */
static void ConstraintInitialize(request, new, args, num_args)
Widget request, new;
ArgList args;
Cardinal *num_args;
{
FormConstraints form = (FormConstraints)new->core.constraints;
FormWidget fw = (FormWidget)new->core.parent;
form->form.virtual_width = (int) new->core.width;
form->form.virtual_height = (int) new->core.height;
if (form->form.dx == default_value)
form->form.dx = fw->form.default_spacing;
if (form->form.dy == default_value)
form->form.dy = fw->form.default_spacing;
form->form.deferred_resize = False;
}
See Also
XtCreateWidget(1),
Constraint(3), Core(3),
Constraint destroy(4), initialize(4), Constraint set_values(4).
Xt - Intrinsics Methods Constraint initialize()