CODE EXAMPLE FOR DART

flutter block rotation

class MyApp extends StatelessWidget {
    @override
    Widget build(BuildContext context) {
    // This vvvv
      SystemChrome.setPreferredOrientations([
        DeviceOrientation.portraitUp,
        DeviceOrientation.portraitDown,
      ]);
    // ^^^^
      return new MaterialApp(...);
    }
  }