main.dart

// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

import 'package:flutter/material.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      debugShowCheckedModeBanner: false,
      theme: ThemeData(
        colorScheme: ColorScheme.fromSeed(seedColor: Colors.deepPurple),
        useMaterial3: true,
      ),
      home: const MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  final String title;

  const MyHomePage({
    super.key,
    required this.title,
  }) : super();

  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  final focus = FocusNode();
  final controller = TextEditingController();

  @override
  void initState() {
    super.initState();
    focus.addListener(() => setState(() {}));
  }
  
  @override
  void dispose() {
    focus.dispose();
    super.dispose();
  }
  
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        backgroundColor: Theme.of(context).colorScheme.inversePrimary,
        title: Text(widget.title),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            Flexible(
              child: TextField(
                focusNode: focus,
                controller: controller,
                onChanged: (_) => setState((){}),
              ),
            ),
            if (focus.hasFocus && controller.value.text.isNotEmpty) const Text('ON FOCUS'),
          ],
        ),
      ),
    );
  }
}