the callback to connect to the "activate" signal of the
action. Since GLib 2.40, this can be null for stateful
actions, in which case the default handler is used. For
boolean-stated actions with no parameter, this is a
toggle. For other state types (and parameter type equal
to the state type) this will be a function that
just calls @change_state (which you should provide).
the callback to connect to the "activate" signal of the action. Since GLib 2.40, this can be null for stateful actions, in which case the default handler is used. For boolean-stated actions with no parameter, this is a toggle. For other state types (and parameter type equal to the state type) this will be a function that just calls @change_state (which you should provide).