How to change app state in Settings component

[VladTheJunior]

I have setting item like this:

  SettingItem::new(
                                "Dark mode",
                                SettingField::switch(
                                    |cx| cx.theme().is_dark(),
                                    |_, cx| {
                                        Theme::change(cx.theme().mode.toggle(), None, cx);
                                    },
                                ),
                            )

It changes theme in app context, but how to change app state ( for example state is struct HelloWorld {mode: ThemeMode})? On Button I can use cx.listener and change it accessing this field