destroy()destroy()Namedestroy - Object class method called when a widget is destroyed.
Synopsis
typedef void (*XtWidgetProc)(Widget);
Widget w;
Inputs
w Specifies the widget that is being destroyed.
Description
The destroy() method is registered on the destroy field of the Object,
RectObj, or Core class part structures. It is invoked by XtDestroyWid‐
get() as part of the destruction process when any widget or object is
destroyed, and should deallocate any memory or resources associated
with the part of the widget instance structure specific to this class.
It does not free the widget instance structure itself.
The destroy() methods of a widget class and all its superclasses are
called in subclass-to-superclass order. (Note that this is the reverse
of the usual superclass-to-subclass chaining sequence.) The destroy()
method of a widget class should deallocate memory or other resources
that were explicitly allocated by this class. Any resource that was
obtained from the resource database or passed in an argument list was
not created by the widget and therefore should not be destroyed by it
(unless the widget allocated memory to copy the resource value, in
which case the memory must be freed).
To reclaim memory, at least the following deallocations should be per‐
formed:
· Call XtFree() on dynamic storage allocated with XtCalloc(), XtMal‐
loc(), etc.
· Call XFreePixmap() on pixmaps created with direct Xlib calls.
· Call XtReleaseGC() on GCs allocated with XtGetGC().
· Call XFreeGC() on GCs allocated with direct Xlib calls.
· Call XtRemoveEventHandler() on event handlers added with XtAddEven‐
tHandler().
· Call XtRemoveTimeOut() on timers created with XtAppAddTimeOut().
· Call XtDestroyWidget() for each child if the widget has children and
is not a subclass of compositeWidgetClass.
The destroy() method is chained, so it cannot be inherited. If a wid‐
get does not need to deallocate any storage, the destroy field in its
widget class record should be NULL.
See XtDestroyWidget(1) for details on the process of widget destruc‐
tion.
Usage
In general, a destroy() method will deallocate any resources allocated
in the initialize() and set_values() methods. This often includes GCs,
pixmaps, and any copies that were made of string resources.
Example
The following procedure is the destroy() method of the Xaw Label wid‐
get. It frees the copy it made of its label string resource, deallo‐
cates two shared GCs, and frees the stipple pixmap it used to draw
itself in insensitive mode.
static void Destroy(w)
Widget w;
{
LabelWidget lw = (LabelWidget)w;
XtFree( lw->label.label );
XtReleaseGC( w, lw->label.normal_GC );
XtReleaseGC( w, lw->label.gray_GC);
XmuReleaseStippledPixmap( XtScreen(w), lw->label.stipple );
}
See AlsoXtDestroyWidget(1),
Core(3),
Constraint destroy(4), initialize(4), set_values(4).
Xt - Intrinsics Methods destroy()
