Expading cards - by Simon Lightfoot 21/12/2020

expand_card.dart

// MIT License
//
// Copyright (c) 2020 Simon Lightfoot
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.
//
import 'dart:math' as math;

import 'package:flutter/material.dart';

void main() {
  runApp(
    MaterialApp(
      debugShowCheckedModeBanner: false,
      home: Example(),
    ),
  );
}

@immutable
class Example extends StatelessWidget {
  const Example({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      backgroundColor: Colors.grey.shade300,
      body: DefaultTextStyle.merge(
        style: TextStyle(
          color: Colors.grey.shade700,
        ),
        child: ListView.builder(
          padding: const EdgeInsets.symmetric(horizontal: 24.0),
          itemCount: 30,
          itemBuilder: (BuildContext context, int index) {
            return ExpandingCard(
              key: Key('item-$index'),
              leading: SizedBox(
                width: 56.0,
                child: DecoratedBox(
                  decoration: BoxDecoration(
                    color: Colors.grey,
                    shape: BoxShape.circle,
                  ),
                  child: AspectRatio(
                    aspectRatio: 1.0,
                    child: Center(
                      child: Text(
                        'Hello',
                        style: TextStyle(color: Colors.white),
                      ),
                    ),
                  ),
                ),
              ),
              title: 'Item #$index',
              subtitle: 'Sub title $index',
              children: [
                InfoPage(index: 3),
                InfoPage(index: 1),
                InfoPage(index: 2),
              ],
            );
          },
        ),
      ),
    );
  }
}

@immutable
class ExpandingCard extends StatefulWidget {
  const ExpandingCard({
    Key? key,
    this.leading,
    required this.title,
    this.subtitle,
    this.expandHeight = 156.0,
    required this.children,
  }) : super(key: key);

  final Widget? leading;
  final String title;
  final String? subtitle;
  final double expandHeight;
  final List<Widget> children;

  @override
  _ExpandingCardState createState() => _ExpandingCardState();
}

class _ExpandingCardState extends State<ExpandingCard> with AutomaticKeepAliveClientMixin {
  late final PageController _pageController;
  bool _expanded = false;

  @override
  bool get wantKeepAlive => _expanded;

  @override
  void initState() {
    super.initState();
    _pageController = PageController();
  }

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

  void _onTap() {
    setState(() => _expanded = !_expanded);
  }

  @override
  Widget build(BuildContext context) {
    final style = DefaultTextStyle.of(context).style;
    final color = style.color ?? Colors.grey;
    super.build(context); // AutomaticKeepAliveClientMixin
    return Card(
      child: DefaultTextStyle.merge(
        style: style,
        child: IconTheme.merge(
          data: IconThemeData(
            color: color,
          ),
          child: InkWell(
            onTap: _onTap,
            child: Stack(
              alignment: Alignment.bottomCenter,
              children: [
                Column(
                  mainAxisSize: MainAxisSize.min,
                  children: [
                    Padding(
                      padding: const EdgeInsets.all(8.0),
                      child: Row(
                        children: [
                          if (widget.leading != null) widget.leading!,
                          const SizedBox(width: 8.0),
                          Column(
                            mainAxisSize: MainAxisSize.min,
                            crossAxisAlignment: CrossAxisAlignment.start,
                            children: [
                              Text(
                                widget.title,
                                style: TextStyle(
                                  fontSize: 18.0,
                                ),
                              ),
                              if (widget.subtitle != null)
                                Text(
                                  widget.subtitle!,
                                  style: TextStyle(
                                    fontSize: 16.0,
                                  ),
                                ),
                            ],
                          ),
                        ],
                      ),
                    ),
                    AnimatedContainer(
                      duration: const Duration(milliseconds: 300),
                      curve: Curves.easeInOut,
                      height: _expanded ? widget.expandHeight : 0.0,
                      child: ShaderMask(
                        shaderCallback: (Rect bounds) {
                          final height = math.min(16.0, bounds.height);
                          return LinearGradient(
                            begin: Alignment.topCenter,
                            end: Alignment.bottomCenter,
                            colors: [Colors.white, Colors.transparent],
                          ).createShader(Rect.fromLTWH(
                            bounds.left,
                            bounds.bottom - height,
                            bounds.width,
                            height,
                          ));
                        },
                        child: ClipRect(
                          child: OverflowBox(
                            alignment: Alignment.topCenter,
                            minHeight: widget.expandHeight,
                            maxHeight: widget.expandHeight,
                            child: Column(
                              children: [
                                Expanded(
                                  child: PageView.builder(
                                    controller: _pageController,
                                    itemCount: widget.children.length,
                                    itemBuilder: (BuildContext context, int index) {
                                      return Padding(
                                        padding: const EdgeInsets.fromLTRB(16.0, 8.0, 16.0, 0.0),
                                        child: widget.children[index],
                                      );
                                    },
                                  ),
                                ),
                                AnimatedBuilder(
                                  animation: _pageController,
                                  builder: (BuildContext context, Widget? child) {
                                    return LayoutBuilder(
                                      builder: (BuildContext context, BoxConstraints constraints) {
                                        final pos = _pageController.position;
                                        if (!pos.hasContentDimensions) {
                                          return SizedBox(height: 24.0);
                                        }
                                        final total =
                                            (pos.maxScrollExtent + pos.viewportDimension) /
                                                pos.viewportDimension;
                                        final page = _pageController.page!.round();
                                        return Padding(
                                          padding: const EdgeInsets.all(6.0),
                                          child: SizedBox(
                                            width: double.infinity,
                                            height: 12.0,
                                            child: Row(
                                              mainAxisAlignment: MainAxisAlignment.center,
                                              children: [
                                                for (int i = 0; i < total; i++) ...[
                                                  DecoratedBox(
                                                    decoration: ShapeDecoration(
                                                      shape: CircleBorder(
                                                        side: BorderSide(color: color, width: 2.0),
                                                      ),
                                                      color: i == page ? color : null,
                                                    ),
                                                    child: AspectRatio(aspectRatio: 1.0),
                                                  ),
                                                  if (i < total - 1) const SizedBox(width: 8.0),
                                                ],
                                              ],
                                            ),
                                          ),
                                        );
                                      },
                                    );
                                  },
                                ),
                                const SizedBox(height: 16.0),
                              ],
                            ),
                          ),
                        ),
                      ),
                    ),
                  ],
                ),
                Positioned(
                  width: 64.0,
                  height: 6.0,
                  bottom: 6.0,
                  child: DecoratedBox(
                    decoration: ShapeDecoration(
                      shape: StadiumBorder(),
                      color: color,
                    ),
                  ),
                ),
              ],
            ),
          ),
        ),
      ),
    );
  }
}

@immutable
class InfoPage extends StatelessWidget {
  const InfoPage({
    Key? key,
    required this.index,
  }) : super(key: key);

  final int index;

  @override
  Widget build(BuildContext context) {
    return Column(
      crossAxisAlignment: CrossAxisAlignment.stretch,
      children: [
        Text(
          'Info $index',
          style: TextStyle(
            fontWeight: FontWeight.bold,
          ),
        ),
        const SizedBox(height: 6.0),
        Expanded(
          child: Text(
            'Lorem ipsum dolor sit amet,\nconsectetur adipiscin elit. Pellentesque laoreet dictum viverra. In in enim sed urna auctor posuere eu at dui. Donec magna odio, ultricies ac ipsum non, aliquet consectetur nisl. Cras.',
            overflow: TextOverflow.ellipsis,
            maxLines: 5,
          ),
        ),
      ],
    );
  }
}