[PyQt] Signal filtering based on arguments

[Kovid Goyal]

weakref.ref() and sip.isdeleted() if you want the config object to store
a list of listeners.

Kovid.

On Wed, Oct 08, 2014 at 08:20:42AM +0200, Florian Bruhin wrote:
> Hi,
> 
> I have an issue which I don't really know to solve properly, maybe
> someone has an idea here.
> 
> My application has a configuration structured into sections and
> options. The user can change the config from inside the application,
> and everything should update/reinitialize correctly on a change, so no
> restart of the application is needed.
> 
> I have a global Config object which stores the configuration and has a
> "changed" signal, with the section/option as a parameter.
> 
> Now I have a lot of "on_config_changed" slots in many different
> objects, and most of the time these are only interested in a few
> options - only if these are changed they have to take action (for
> example call setStyleSheet again because a configured color/font
> changed).
> 
> My original solution was simply having these slots, connecting them in
> a central place (where I create the config object) and checking inside
> each slot if it is interested in the event.
> 
> As this was rather unpractical, I tried switching to a solution where
> every object calls  `config.on_change(section, option, callback)`. The
> config module then saves a (section, option, callback) tuple in a list
> of callback handlers, and calls the appropriate callbacks on a change.
> 
> The implementation is here:
> https://github.com/The-Compiler/qutebrowser/blob/b49b227c0d1ba7a580749f1572729311263ba299/qutebrowser/config/config.py#L46-L70
> 
> Now the problem is this keeps references to methods of objects which
> might get deleted by Qt at some point (for example when I open a
> new window, the change handlers get registered, and when I close it
> again the window is deleted but the change handler is still present).
> 
> I tried passing the underlying object to on_change which then uses the
> `destroyed` signal emitted by Qt to remove the handler if the object
> gets destroyed, but for some reason I still got RuntimeError's because
> "self" wasn't existent anymore in the change handlers.
> 
> At this point I think reverting back to my original approach would be
> the better idea :D
> 
> Some ideas I had to make it more bearable:
> 
> - Use a decorator for the on_config_changed slots to easily check if
>   it's a `changed`-signal we're interested in and return if not.
> 
> - Connect the slots directly in __init__ of the consumer objects
>   instead of a central place.
> 
> Does anyone else have a better idea I've not thought of yet?
> 
> Florian
> 
> -- 
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-- 
_____________________________________

Dr. Kovid Goyal 
http://www.kovidgoyal.net
http://calibre-ebook.com
_____________________________________
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