flutter/examples/api/lib/widgets/focus_traversal/focus_traversal_group.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.

// Flutter code sample for FocusTraversalGroup

import 'package:flutter/material.dart';

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

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

  static const String _title = 'Flutter Code Sample';

  @override
  Widget build(BuildContext context) {
    return const MaterialApp(
      title: _title,
      home: MyStatelessWidget(),
    );
  }
}

/// A button wrapper that adds either a numerical or lexical order, depending on
/// the type of T.
class OrderedButton<T> extends StatefulWidget {
  const OrderedButton({
    Key? key,
    required this.name,
    this.canRequestFocus = true,
    this.autofocus = false,
    required this.order,
  }) : super(key: key);

  final String name;
  final bool canRequestFocus;
  final bool autofocus;
  final T order;

  @override
  State<OrderedButton<T>> createState() => _OrderedButtonState<T>();
}

class _OrderedButtonState<T> extends State<OrderedButton<T>> {
  late FocusNode focusNode;

  @override
  void initState() {
    super.initState();
    focusNode = FocusNode(
      debugLabel: widget.name,
      canRequestFocus: widget.canRequestFocus,
    );
  }

  @override
  void dispose() {
    focusNode.dispose();
    super.dispose();
  }

  @override
  void didUpdateWidget(OrderedButton<T> oldWidget) {
    super.didUpdateWidget(oldWidget);
    focusNode.canRequestFocus = widget.canRequestFocus;
  }

  void _handleOnPressed() {
    focusNode.requestFocus();
    print('Button ${widget.name} pressed.');
    debugDumpFocusTree();
  }

  @override
  Widget build(BuildContext context) {
    FocusOrder order;
    if (widget.order is num) {
      order = NumericFocusOrder((widget.order as num).toDouble());
    } else {
      order = LexicalFocusOrder(widget.order.toString());
    }

    Color? overlayColor(Set<MaterialState> states) {
      if (states.contains(MaterialState.focused)) {
        return Colors.red;
      }
      if (states.contains(MaterialState.hovered)) {
        return Colors.blue;
      }
      return null; // defer to the default overlayColor
    }

    Color? foregroundColor(Set<MaterialState> states) {
      if (states.contains(MaterialState.focused) ||
          states.contains(MaterialState.hovered)) {
        return Colors.white;
      }
      return null; // defer to the default foregroundColor
    }

    return FocusTraversalOrder(
      order: order,
      child: Padding(
        padding: const EdgeInsets.all(8.0),
        child: OutlinedButton(
          focusNode: focusNode,
          autofocus: widget.autofocus,
          style: ButtonStyle(
            overlayColor:
                MaterialStateProperty.resolveWith<Color?>(overlayColor),
            foregroundColor:
                MaterialStateProperty.resolveWith<Color?>(foregroundColor),
          ),
          onPressed: () => _handleOnPressed(),
          child: Text(widget.name),
        ),
      ),
    );
  }
}

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

  @override
  Widget build(BuildContext context) {
    return Container(
      color: Colors.white,
      child: FocusTraversalGroup(
        policy: OrderedTraversalPolicy(),
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            // A group that is ordered with a numerical order, from left to right.
            FocusTraversalGroup(
              policy: OrderedTraversalPolicy(),
              child: Row(
                mainAxisAlignment: MainAxisAlignment.center,
                children: List<Widget>.generate(3, (int index) {
                  return OrderedButton<num>(
                    name: 'num: $index',
                    // TRY THIS: change this to "3 - index" and see how the order changes.
                    order: index,
                  );
                }),
              ),
            ),
            // A group that is ordered with a lexical order, from right to left.
            FocusTraversalGroup(
              policy: OrderedTraversalPolicy(),
              child: Row(
                mainAxisAlignment: MainAxisAlignment.center,
                children: List<Widget>.generate(3, (int index) {
                  // Order as "C" "B", "A".
                  final String order =
                      String.fromCharCode('A'.codeUnitAt(0) + (2 - index));
                  return OrderedButton<String>(
                    name: 'String: $order',
                    order: order,
                  );
                }),
              ),
            ),
            // A group that orders in widget order, regardless of what the order is set to.
            FocusTraversalGroup(
              // Note that because this is NOT an OrderedTraversalPolicy, the
              // assigned order of these OrderedButtons is ignored, and they
              // are traversed in widget order. TRY THIS: change this to
              // "OrderedTraversalPolicy()" and see that it now follows the
              // numeric order set on them instead of the widget order.
              policy: WidgetOrderTraversalPolicy(),
              child: Row(
                mainAxisAlignment: MainAxisAlignment.center,
                children: List<Widget>.generate(3, (int index) {
                  return OrderedButton<num>(
                    name: 'ignored num: ${3 - index}',
                    order: 3 - index,
                  );
                }),
              ),
            ),
          ],
        ),
      ),
    );
  }
}