[Fwd: Re: Segfault with set_set_scroll_adjustments_signals and gnome.ui]

[Herwig Hochleitner]

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BJörn Lindqvist schrieb:

> Hi,
>
> 2008/8/29 Herwig Hochleitner <hhochleitner@...>:
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>>
>> Hello!
>> My Custom DrawingArea keeps segfaulting me on being destroyed.
>> I traced it down to the following minimal example:
>>
>> [PYTHON]
>>
>> import gtk
>> import gobject
>> import gnome.ui
>>
>> class CustomDrawingArea(gtk.DrawingArea):
>>    __gsignals__ = {"set-scroll-adjustments" : (gobject.SIGNAL_RUN_LAST,
>> gobject.TYPE_BOOLEAN,
>>                                                (gobject.TYPE_OBJECT,
>> gobject.TYPE_OBJECT))}
>>
>>    def __init__(self):
>>        gtk.DrawingArea.__init__(self)
>>        self.set_set_scroll_adjustments_signal("set-scroll-adjustments")
>>
>>    def do_set_scroll_adjustments(self, hadjustment, vadjustment):
>>        return False
>>
>> gobject.type_register(CustomDrawingArea)
>>
>> if __name__ == "__main__":
>>    win = gtk.Window()
>>    swin = gtk.ScrolledWindow()
>>    da = CustomDrawingArea()
>>    win.add(swin)
>>    swin.add(da)
>>    win.show_all()
>>    gtk.main()
>>
>> [/PYTHON]
>
> There are actually two different bugs at work here.
>
>> The segfault happens when deleting the window
>
> See http://bugzilla.gnome.org/show_bug.cgi?id=551699. When you delete
> a window, you invoke that windows destroy() method which is supposed
> to free up its references to other widgets. Except that it often
> doesn't work because many widgets implement the destroy/finalize
> scheme wrongly. Others may disagree, but I think it is best to always
> terminate your applications using sys.exit(), that way you don't have
> to deal with all the problems in gtk's object destruction system.

That clarifies things somewhat. I saw that behavior on several gtk apps

and therefore wouldn't have cared that much. But the problem was that my
widget gets reconstructed everytime the user changes the data.

>
>> or removing the custom widget from the scrolled window (in my
>> application this happens dynamically).
>
> I think this happens because your set-scroll-adjustments signal
> prototype is wrong. It should return None, not a bool. Like this:
>
>     __gsignals__ = {
>         "set-scroll-adjustments" : (gobject.SIGNAL_RUN_LAST,
>                                     bool,
>                                     (gtk.Adjustment, gtk.Adjustment))}
>
> Gtk isn't smart enough to check that your signal prototype is correct
> before calling it.

I see. I was mislead on that because gtk.Widget.set_scroll_adjustments()

returns a boolean.
Everything works now, thanks a lot.

I suppose it would be possible to check the correctnes of signal
overrides in gobject, wouldn't it?

regards
Herwig Hochleitner

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