void main() {
  runApp(const MyApp());
}

class KeyboardPage extends StatefulWidget {
  const KeyboardPage({Key? key}) : super(key: key);

  @override
  State<KeyboardPage> createState() => _KeyboardPageState();
}

class _KeyboardPageState extends State<KeyboardPage> {
  FocusNode node = FocusNode();

  @override
  void initState() {
    super.initState();
    node.addListener(() {
      setState(() {});
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Column(
        mainAxisAlignment: MainAxisAlignment.center,
        children: <Widget>[
          Text(
            node.hasFocus ? 'focus' : 'unfocus',
            style: const TextStyle(fontSize: 26, color: Colors.black),
          ),
          CupertinoTextField(
            focusNode: node,
            decoration: const BoxDecoration(color: Colors.red),
          )
        ],
      ),
    );
  }
}