gtk2/docs/developers.txt

Things to care about when using/programing for GTK+
===================================================

This file is meant to collect some frequently triggered failures when
programming for/with Gtk, having the spirit of a developers FAQ.
It is also the correct place to list up things that programmers should
care about in general.

In the hope that this text might be useful to someone,

        - Tim Janik <timj@gimp.org>
          1998/02/11


Automatic destruction of widgets on removal from parent
-------------------------------------------------------

This is a reference counting issue, you would want to refer
to refcounting.txt on it.


What are all the widget flags about?
------------------------------------

Refer to the file widget_system.txt which covers widget flags and the
resulting invariants in a detailed way.


GdkWindow pointers may be NULL in GdkEvents
-------------------------------------------

The notification nature of the signal mechanism might cause events to
be emitted that have their GdkWindow pointer set to NULL.
This is due to the fact that certain events need to be emitted after the
real GdkWindow of a widget is not any longer pertinent.
It's up to the signal handling function (application) to check for the
window field of the event structure to be != NULL, if it is going to
perform any operations through Gdk calls on it.
Events that a likely to trigger a missing check for the window pointer
currently are (and correspond to the trailing signals):

GDK_SELECTION_CLEAR     GtkWidget::selection_clear_event
GDK_FOCUS_CHANGE        GtkWidget::focus_in_event
                        GtkWidget::focus_out_event

Events that are assured to have a valid GdkEvent.any.window field are

GDK_EXPOSE		GtkWidget::expose_event


Writing Gdk functions
---------------------

When writing Gdk functions that operate on GdkWindow structures in any
meaningful sense, that is casting to a GdkWindowPrivate structure for
access to fields other then GdkWindow.user_data, the programmer is
recommended to check for the GdkWindowPrivate.destroyed field to be ==
FALSE, especially if the GdkWindowPrivate.xwindow field is used.
Silent abortion of the Gdk function is the correct behaviour if this
condition isn't met.