flutter_without_widgets_app.dart

import 'package:flutter/services.dart';
import 'package:flutter/widgets.dart';

class App extends StatefulWidget {
  final Widget root;

  const App({
    super.key,
    required this.root
  });

  @override
  AppState createState() {
    return AppState();
  }
}

class AppState extends State<App> with WidgetsBindingObserver {
  final focusNode = FocusNode();
  final focusScopeNode = FocusScopeNode();
  final scrollController = ScrollController();

  @override
  void initState() {
    super.initState();
    WidgetsBinding.instance.addObserver(this);
  }

  @override
  Widget build(BuildContext context) {
    return RootRestorationScope(
      restorationId: null,
      child: SharedAppData(
        child: Shortcuts(
          shortcuts: const {
            SingleActivator(LogicalKeyboardKey.tab): NextFocusIntent()
          },
          child: DefaultTextEditingShortcuts(
            child: Actions(
              actions: {
                NextFocusIntent: NextFocusAction()
              },
              child: FocusTraversalGroup(
                policy: ReadingOrderTraversalPolicy(),
                child: ShortcutRegistrar(
                  child: MediaQuery.fromWindow(
                    child: Localizations(
                      locale: const Locale('en'),
                      delegates: const [
                        DefaultWidgetsLocalizations.delegate
                      ],
                      child: Builder(
                        builder: (context) {
                          return PrimaryScrollController(
                            controller: scrollController,
                            child: FocusScope(
                              node: focusScopeNode,
                              child: RepaintBoundary(
                                child: Focus(
                                  focusNode: focusNode,
                                  autofocus: true,
                                  skipTraversal: true,
                                  includeSemantics: false,
                                  child: widget.root,
                                )
                              )
                            )
                          );
                        }
                      )
                    )
                  )
                )
            )
            )
          )
        )
      )
    );
  }
}

class FocusableContainer extends StatefulWidget {

  const FocusableContainer({ super.key });

  @override
  FocusableContainerState createState() {
    return FocusableContainerState();
  }
}

class FocusableContainerState extends State {
  bool hasFocus = false;

  void handleFocusChange(bool focused) {
    setState(() {
      hasFocus = focused;
    });
  }

  @override
  Widget build(BuildContext context) {
    return FocusableActionDetector(
      onFocusChange: handleFocusChange,
      child: Container(
        padding: const EdgeInsets.all(24),
        decoration: BoxDecoration(
          color: hasFocus ? const Color(0xFFCC00CC) : const Color(0xFF0000FF)
        ),
        child: const Text('focus me', style: TextStyle(color: Color(0xFFFFFFFF))),
      )
    );
  }
}

void main() {
  runApp(
    App(
      root: Column(
        children: const [
          FocusableContainer()
        ]
      )
    )
  );
}