Setup a11y programmatically in Python

Platform
, ,
1

Hi,

In the official doc, there is a section explaining how to make a tab-based UI accessible: Gtk – 4.0: GTK Accessibility

Here is my attempt in Python:

import sys
import gi
gi.require_version('Gtk', '4.0')
from gi.repository import GObject, Gtk

class MyApp(Gtk.Application):

    def __init__(self):
        Gtk.Application.__init__(self)
        self.connect('activate', self.on_activate)

    def on_activate(self, app):
        self.add_window(MyAppWindow())

class MyAppWindow(Gtk.ApplicationWindow):

    def __init__(self):
        Gtk.ApplicationWindow.__init__(self, default_width=600, default_height=400)
        # Create widgets
        notebook = Gtk.Box(orientation='vertical')
        header = Gtk.Box(orientation='horizontal', accessible_role='tab-list')
        tab = Gtk.Label(label="Title", accessible_role='tab')
        container = Gtk.Stack(vexpand=True)
        page = container.add_child(Gtk.Label(label="Hello World!"))
        # Accessibility
        tab.update_state([Gtk.AccessibleState.SELECTED], [True])
        tab.update_relation([Gtk.AccessibleRelation.CONTROLS], [page])
        # Packing
        header.append(tab)
        notebook.append(header)
        notebook.append(container)
        self.set_child(notebook)
        self.present()

if __name__ == '__main__':
    sys.exit(MyApp().run(sys.argv))

But that doesn’t work, I get these errors:

test_a11y.py:31: Warning: g_value_get_int: assertion 'G_VALUE_HOLDS_INT (value)' failed
  tab.update_state([Gtk.AccessibleState.SELECTED], [True])
test_a11y.py:32: Warning: g_value_get_pointer: assertion 'G_VALUE_HOLDS_POINTER (value)' failed
  tab.update_relation([Gtk.AccessibleRelation.CONTROLS], [page])

For the SELECTED state, the warning disappears if I use integers like 0 or 1 instead of True/False. Looks weird, the doc says the expected type is “boolean or undefined”…

Regarding the CONTROLS relation, I’m unable to pass a correct value… I tried lots of things, like page, page.__gpointer__, or even GObject.Value(GObject.TYPE_POINTER, page.__gpointer__), without success.

Am I on the right path?

2

You cannot use Python’s boolean objects True or False if an accessible properties expects a boolean or undefined. You need to use 1, for true; 0, for false; or Gtk.ACCESSIBLE_VALUE_UNDEFINED, for undefined.

You need to create a Gtk.AccessibleList, e.g.

rel = Gtk.AccessibleList.new_from_list([page])
tab.update_relation([Gtk.AccessibleRelation.CONTROLS], [rel])
1 Like
3

And in addition to that, you’ll need to make the labels focusable, which they’re not by default, so gtk_widget_set_can_focus and gtk_widget_set_focusable is your friend (I don’t remember exactly whether you’ll need both in the label case).

1 Like
4

Thanks, I indeed missed the AccessibleList stuff.
Seems to work now!

Yeah, good point!
And probably “actionable” too.

5

This topic was automatically closed 30 days after the last reply. New replies are no longer allowed.