[pygtk] Actions for custom widgets in PyGTK

Sascha Silbe silbe at activitycentral.com
Tue Jul 31 04:22:04 WST 2012


Dear readers,

is there any project that has succeeded in making custom widgets using
PyGTK accessible, including adding new actions? I'm having a hard time
trying to do this in Sugar [1]; being able to take a peek at
known-working code would help a lot. Searching the web only turned up
questions and problems, not much in the way of answers and solutions.

My current problem child are Palettes, the Sugar equivalent of context
menus and drop-down menus. They can be attached to many different
widgets (including table cells), but those widgets don't always have a
Palette. There's no API [3] in ATK to add actions to an existing
instance of AtkObject + AtkAction, so I'm trying to provide a custom
AtkObject subclass that overrides the AtkAction methods, but otherwise
just wraps the existing AtkObject. I managed to get it in a form that
doesn't trigger CRITICAL errors (or Tracebacks, for that matter), but it
isn't really working. I don't see any change in sniff, and my custom
get_n_actions() never gets called. The name collisions between AtkObject
and AtkAction [3] will certainly cause trouble (and I have some
work-around code that at least helps on the Python side), but I don't
think they're causing this particular issue. Rather it looks like my
custom AtkObject instance doesn't get used at all on the C side.

Because I need to add the custom wrappers at run-time (as mentioned
above, we don't know beforehand whether a widget will have a Palette or
not), I'm currently hot-patching the get_accessible() method on the fly:

        parent_accessible = parent.get_accessible()
        wrapper = AtkActionWrapper(parent_accessible)
        parent.get_accessible = lambda: wrapper
        wrapper.add_action('menu', _('Invoke Palette'),
                           _('Pop up the Palette'), self.notify_right_click)

I can imagine this hot-patching being problematic, but overriding
get_accessible() in the class definition (instead of hot-patching the
instance afterwards) doesn't help either.

Is there a way of using AtkObject subclasses with GTK subclasses other
than duplicating the entire set of custom widgets (and probably quite a
few stock ones as well) and registering an AtkObject factory for each of
them?

Sascha

[1] https://wiki.sugarlabs.org/go/What_is_Sugar%3F
[2] https://bugzilla.gnome.org/show_bug.cgi?id=649804
[3] https://bugzilla.gnome.org/show_bug.cgi?id=647482
-- 
http://sascha.silbe.org/
http://www.infra-silbe.de/
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