From timj@gimp.org Sat Jan 24 19:15:22 1998
Date: Sat, 24 Jan 1998 18:25:10 +0100 (CET)
From: Tim Janik <timj@gimp.org>
To: Peter Mattis <petm@xcf.berkeley.edu>
Cc: Gtk+ Devils <gtkdev@gimp.org>
Subject: widget destruction while in call

hi peter and gtk+ devils ;)


i've got the following problem, when double clicking on a list item
it's window should be destroyed, because the selection is made.
now this doesn't work 'cause the program is aborted with a
BadWindow error (from X).

this happens because the function that is connected to the lists
button_press_event calls gtk_widget_destroy () on the main window.
then the widget destruction is propagated through the tree until
the list widget should be destroyed. but since the list widget is
still GTK_IN_CALL (from the button_press_event) it isn't destroyed
but only flagged as GTK_NEED_DESTROY. at this point the propagation
stops, and nothing happends to the list widgets children.
after the return of the button_press_event handler, the clicked
list item is now selected/unselected (depends on the previous state).
it therefore updates its GdkWindow (XWindow) by setting the new
backgroundcolor (selected->blue/unselected->white). since it's
parent XWindows are destroyed already the window which the list item
wants to draw on is also destroyed. at this point the BadWindow error
occours cause the XWindow handle has become invalid (the application
already received a destroy notify).

now, solutions might be:
1) check for private->destroyed on *all* gdk call as it's done
   it a lot of places already, or
2) propagate a widget unrealize signal through the tree before
   destroying a widget, or
3) propagate GTK_NEED_DESTROY down the tree (not only flag the
   list container), this would require gtk_object_destroy() to
   return wether the object got actually destroyed or flagged
   only. then prohibit gdk operations on widgets flagged as
   GTK_NEED_DESTROY.

i'm not sure what the best solution might be, but i tend to favour
1) or 3).


---
ciaoTJ