Cleaner hello world example

[chimon2000]

In hello_world_demo.dart, rather than creating a global NavStackController and assigning it in onGenerateStack, it may be better to wire up the keyboard navigation in scaffoldBuilder

Example implementation:

class HelloWorldDemo extends StatelessWidget {
  const HelloWorldDemo({
    Key? key,
  }) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return MaterialApp.router(
      routeInformationParser: NavStackParser(),
      routerDelegate: NavStackDelegate(
        onGenerateStack: (context, nav) => PathStack(
          scaffoldBuilder: (context, child) =>
              KeyboardNavigationScaffold(child: child),
          routes: {
            ["/"]: HomeScreen().toStackRoute(),
            ["/messages"]: MessagesScreen().toStackRoute(),
            ["/profile"]: ProfileScreen().toStackRoute(),
          },
          transitionBuilder: (_, stack, anim1) =>
              FadeTransition(opacity: anim1, child: stack),
        ),
      ),
    );
  }
}

class KeyboardNavigationScaffold extends StatefulWidget {
  const KeyboardNavigationScaffold({
    Key? key,
    this.child,
  }) : super(key: key);

  final Widget? child;

  @override
  _KeyboardNavigationScaffoldState createState() =>
      _KeyboardNavigationScaffoldState();
}

class _KeyboardNavigationScaffoldState
    extends State<KeyboardNavigationScaffold> {
  late final _controller = NavStack.of(context);

  @override
  void initState() {
    super.initState();
    RawKeyboard.instance.addListener((value) {
      if (value is RawKeyDownEvent) {
        if (value.logicalKey == LogicalKeyboardKey.digit1)
          _controller.path = "/login";
        if (value.logicalKey == LogicalKeyboardKey.digit2)
          _controller.path = "/profile";
      }
    });
  }

  @override
  Widget build(BuildContext context) {
    return Container(child: widget.child);
  }
}