flutter/examples/api/lib/widgets/focus_manager/focus_node.0.dart

// Copyright 2014 The Flutter Authors. 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';
import 'package:flutter/services.dart';

/// Flutter code sample for [FocusNode].

void main() => runApp(const FocusNodeExampleApp());

class FocusNodeExampleApp extends StatelessWidget {
  const FocusNodeExampleApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(title: const Text('FocusNode Sample')),
        body: const FocusNodeExample(),
      ),
    );
  }
}

class ColorfulButton extends StatefulWidget {
  const ColorfulButton({super.key});

  @override
  State<ColorfulButton> createState() => _ColorfulButtonState();
}

class _ColorfulButtonState extends State<ColorfulButton> {
  late FocusNode _node;
  bool _focused = false;
  late FocusAttachment _nodeAttachment;
  Color _color = Colors.white;

  @override
  void initState() {
    super.initState();
    _node = FocusNode(debugLabel: 'Button');
    _node.addListener(_handleFocusChange);
    _nodeAttachment = _node.attach(context, onKeyEvent: _handleKeyPress);
  }

  void _handleFocusChange() {
    if (_node.hasFocus != _focused) {
      setState(() {
        _focused = _node.hasFocus;
      });
    }
  }

  KeyEventResult _handleKeyPress(FocusNode node, KeyEvent event) {
    if (event is KeyDownEvent) {
      debugPrint('Focus node ${node.debugLabel} got key event: ${event.logicalKey}');
      switch (event.logicalKey) {
        case LogicalKeyboardKey.keyR:
          debugPrint('Changing color to red.');
          setState(() {
            _color = Colors.red;
          });
          return KeyEventResult.handled;
        case LogicalKeyboardKey.keyG:
          debugPrint('Changing color to green.');
          setState(() {
            _color = Colors.green;
          });
          return KeyEventResult.handled;
        case LogicalKeyboardKey.keyB:
          debugPrint('Changing color to blue.');
          setState(() {
            _color = Colors.blue;
          });
          return KeyEventResult.handled;
      }
    }
    return KeyEventResult.ignored;
  }

  @override
  void dispose() {
    _node.removeListener(_handleFocusChange);
    // The attachment will automatically be detached in dispose().
    _node.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    _nodeAttachment.reparent();
    return GestureDetector(
      onTap: () {
        if (_focused) {
          _node.unfocus();
        } else {
          _node.requestFocus();
        }
      },
      child: Center(
        child: Container(
          width: 400,
          height: 100,
          color: _focused ? _color : Colors.white,
          alignment: Alignment.center,
          child: Text(_focused ? "I'm in color! Press R,G,B!" : 'Press to focus'),
        ),
      ),
    );
  }
}

class FocusNodeExample extends StatelessWidget {
  const FocusNodeExample({super.key});

  @override
  Widget build(BuildContext context) {
    final TextTheme textTheme = Theme.of(context).textTheme;
    return DefaultTextStyle(style: textTheme.headlineMedium!, child: const ColorfulButton());
  }
}