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.