Can provider get and set states without widget context?

[buptyyf]

I want to change AppState themeMode out of widget, how can I get the instance of appState?

Example code as follow:

void main {
  runApp(MultiProvider(
    providers: [
      ChangeNotifierProvider(create: (context) => AppState()),
    ],
    child: const MyApp(),
  ));
}

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    AppState appState = context.watch<AppState>();
    return MaterialApp(
      restorationScopeId: "desktop-demo1",
      title: 'myapp',
      themeMode: appState.themeMode,
      home: Container(),
    );
  }
}

class AppState extends ChangeNotifier {
  ThemeMode _themeMode = ThemeMode.system;

  ThemeMode get themeMode => _themeMode;
  set themeMode(val) {
    _themeMode = val;
    notifyListeners();
  }
}

class DataController {
   changeState() {
   // I want to change AppState themeMode here, how can I get the instance of appState?
}
}

Thanks in advance!