Getting notification for GObject with custom param

Platform
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1

Hey folks,

I’m exploring properties and signals in Python, following from the documentation:

https://pygobject.gnome.org/guide/api/properties.html
https://pygobject.gnome.org/guide/api/signals.html

I’d like to create Gtk.Template classes with custom parameters. It wasn’t working so I made a very simple test case:

from gi.repository import GObject


class Meaning(GObject.Object):
    def __init__(self):
        super().__init__()
        self._meaning_of_life = 42

    @GObject.Property(type=int)
    def meaning_of_life(self):
        return self._meaning_of_life

    @meaning_of_life.setter
    def meaning_of_life(self, new_meaning):
        self._meaning_of_life = new_meaning


def meaning_fn(instance, param):
    print("The meaning of life has been redefined.")


meaning = Meaning()
meaning.set_property("meaning_of_life", 43)
meaning.connect("notify::meaning_of_life", meaning_fn)

My meaning_fn() callback isn’t called. Why is that?

Thanks again,

J.R.

2

You’re connecting to the signal after setting the property. Signals are synchronous, and so are property accessors.

Additionally, you’re using the wrong detail for the notify signal: the detail must be the canonical property name. See:

If you change the main section with this:

meaning = Meaning()
meaning.connect("notify::meaning-of-life", meaning_fn)
meaning.set_property("meaning-of-life", 43)

You’ll see the correct result on your terminal:

❯ python3 ./property-notify.py
The meaning of life has been redefined.
3

Aha!

In my defense, the order of set_property() and connect() was a cut-and-paste error from my unit tests.

The canonical name was the problem.

Thanks again!

4

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