examples/api/lib/widgets/basic/flow.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';

/// Flutter code sample for [Flow].

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

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

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

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

  @override
  State<FlowMenu> createState() => _FlowMenuState();
}

class _FlowMenuState extends State<FlowMenu>
    with SingleTickerProviderStateMixin {
  late AnimationController menuAnimation;
  IconData lastTapped = Icons.notifications;
  final List<IconData> menuItems = <IconData>[
    Icons.home,
    Icons.new_releases,
    Icons.notifications,
    Icons.settings,
    Icons.menu,
  ];

  void _updateMenu(IconData icon) {
    if (icon != Icons.menu) {
      setState(() => lastTapped = icon);
    }
  }

  @override
  void initState() {
    super.initState();
    menuAnimation = AnimationController(
      duration: const Duration(milliseconds: 250),
      vsync: this,
    );
  }

  Widget flowMenuItem(IconData icon) {
    final double buttonDiameter =
        MediaQuery.widthOf(context) / menuItems.length;
    return Padding(
      padding: const .symmetric(vertical: 8.0),
      child: RawMaterialButton(
        fillColor: lastTapped == icon ? Colors.amber[700] : Colors.blue,
        splashColor: Colors.amber[100],
        shape: const CircleBorder(),
        constraints: BoxConstraints.tight(Size(buttonDiameter, buttonDiameter)),
        onPressed: () {
          _updateMenu(icon);
          menuAnimation.status == AnimationStatus.completed
              ? menuAnimation.reverse()
              : menuAnimation.forward();
        },
        child: Icon(icon, color: Colors.white, size: 45.0),
      ),
    );
  }

  @override
  Widget build(BuildContext context) {
    return Flow(
      delegate: FlowMenuDelegate(menuAnimation: menuAnimation),
      children: menuItems
          .map<Widget>((IconData icon) => flowMenuItem(icon))
          .toList(),
    );
  }
}

class FlowMenuDelegate extends FlowDelegate {
  FlowMenuDelegate({required this.menuAnimation})
    : super(repaint: menuAnimation);

  final Animation<double> menuAnimation;

  @override
  bool shouldRepaint(FlowMenuDelegate oldDelegate) {
    return menuAnimation != oldDelegate.menuAnimation;
  }

  @override
  void paintChildren(FlowPaintingContext context) {
    double dx = 0.0;
    for (int i = 0; i < context.childCount; ++i) {
      dx = context.getChildSize(i)!.width * i;
      context.paintChild(
        i,
        transform: Matrix4.translationValues(dx * menuAnimation.value, 0, 0),
      );
    }
  }
}