examples/flutter_gallery/lib/demo/material/expansion_panels_demo.dart

// Copyright 2016 The Chromium 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';

enum _Location {
  Barbados,
  Bahamas,
  Bermuda
}

typedef Widget DemoItemBodyBuilder<T>(DemoItem<T> item);
typedef String ValueToString<T>(T value);

class DualHeaderWithHint extends StatelessWidget {
  const DualHeaderWithHint({
    this.name,
    this.value,
    this.hint,
    this.showHint
  });

  final String name;
  final String value;
  final String hint;
  final bool showHint;

  Widget _crossFade(Widget first, Widget second, bool isExpanded) {
    return new AnimatedCrossFade(
      firstChild: first,
      secondChild: second,
      firstCurve: const Interval(0.0, 0.6, curve: Curves.fastOutSlowIn),
      secondCurve: const Interval(0.4, 1.0, curve: Curves.fastOutSlowIn),
      sizeCurve: Curves.fastOutSlowIn,
      crossFadeState: isExpanded ? CrossFadeState.showSecond : CrossFadeState.showFirst,
      duration: const Duration(milliseconds: 200),
    );
  }

  @override
  Widget build(BuildContext context) {
    final ThemeData theme = Theme.of(context);
    final TextTheme textTheme = theme.textTheme;

    return new Row(
      children: <Widget>[
        new Expanded(
          flex: 2,
          child: new Container(
            margin: const EdgeInsets.only(left: 24.0),
            child: new FittedBox(
              fit: BoxFit.scaleDown,
              alignment: Alignment.centerLeft,
              child: new Text(
                name,
                style: textTheme.body1.copyWith(fontSize: 15.0),
              ),
            ),
          ),
        ),
        new Expanded(
          flex: 3,
          child: new Container(
            margin: const EdgeInsets.only(left: 24.0),
            child: _crossFade(
              new Text(value, style: textTheme.caption.copyWith(fontSize: 15.0)),
              new Text(hint, style: textTheme.caption.copyWith(fontSize: 15.0)),
              showHint
            )
          )
        )
      ]
    );
  }
}

class CollapsibleBody extends StatelessWidget {
  const CollapsibleBody({
    this.margin = EdgeInsets.zero,
    this.child,
    this.onSave,
    this.onCancel
  });

  final EdgeInsets margin;
  final Widget child;
  final VoidCallback onSave;
  final VoidCallback onCancel;

  @override
  Widget build(BuildContext context) {
    final ThemeData theme = Theme.of(context);
    final TextTheme textTheme = theme.textTheme;

    return new Column(
      children: <Widget>[
        new Container(
          margin: const EdgeInsets.only(
            left: 24.0,
            right: 24.0,
            bottom: 24.0
          ) - margin,
          child: new Center(
            child: new DefaultTextStyle(
              style: textTheme.caption.copyWith(fontSize: 15.0),
              child: child
            )
          )
        ),
        const Divider(height: 1.0),
        new Container(
          padding: const EdgeInsets.symmetric(vertical: 16.0),
          child: new Row(
            mainAxisAlignment: MainAxisAlignment.end,
            children: <Widget>[
              new Container(
                margin: const EdgeInsets.only(right: 8.0),
                child: new FlatButton(
                  onPressed: onCancel,
                  child: const Text('CANCEL', style: const TextStyle(
                    color: Colors.black54,
                    fontSize: 15.0,
                    fontWeight: FontWeight.w500
                  ))
                )
              ),
              new Container(
                margin: const EdgeInsets.only(right: 8.0),
                child: new FlatButton(
                  onPressed: onSave,
                  textTheme: ButtonTextTheme.accent,
                  child: const Text('SAVE')
                )
              )
            ]
          )
        )
      ]
    );
  }
}

class DemoItem<T> {
  DemoItem({
    this.name,
    this.value,
    this.hint,
    this.builder,
    this.valueToString
  }) : textController = new TextEditingController(text: valueToString(value));

  final String name;
  final String hint;
  final TextEditingController textController;
  final DemoItemBodyBuilder<T> builder;
  final ValueToString<T> valueToString;
  T value;
  bool isExpanded = false;

  ExpansionPanelHeaderBuilder get headerBuilder {
    return (BuildContext context, bool isExpanded) {
      return new DualHeaderWithHint(
        name: name,
        value: valueToString(value),
        hint: hint,
        showHint: isExpanded
      );
    };
  }

  Widget build() => builder(this);
}

class ExpansionPanelsDemo extends StatefulWidget {
  static const String routeName = '/material/expansion_panels';

  @override
  _ExpansionPanelsDemoState createState() => new _ExpansionPanelsDemoState();
}

class _ExpansionPanelsDemoState extends State<ExpansionPanelsDemo> {
  List<DemoItem<dynamic>> _demoItems;

  @override
  void initState() {
    super.initState();

    _demoItems = <DemoItem<dynamic>>[
      new DemoItem<String>(
        name: 'Trip',
        value: 'Caribbean cruise',
        hint: 'Change trip name',
        valueToString: (String value) => value,
        builder: (DemoItem<String> item) {
          void close() {
            setState(() {
              item.isExpanded = false;
            });
          }

          return new Form(
            child: new Builder(
              builder: (BuildContext context) {
                return new CollapsibleBody(
                  margin: const EdgeInsets.symmetric(horizontal: 16.0),
                  onSave: () { Form.of(context).save(); close(); },
                  onCancel: () { Form.of(context).reset(); close(); },
                  child: new Padding(
                    padding: const EdgeInsets.symmetric(horizontal: 16.0),
                    child: new TextFormField(
                      controller: item.textController,
                      decoration: new InputDecoration(
                        hintText: item.hint,
                        labelText: item.name,
                      ),
                      onSaved: (String value) { item.value = value; },
                    ),
                  ),
                );
              },
            ),
          );
        },
      ),
      new DemoItem<_Location>(
        name: 'Location',
        value: _Location.Bahamas,
        hint: 'Select location',
        valueToString: (_Location location) => location.toString().split('.')[1],
        builder: (DemoItem<_Location> item) {
          void close() {
            setState(() {
              item.isExpanded = false;
            });
          }
          return new Form(
            child: new Builder(
              builder: (BuildContext context) {
                return new CollapsibleBody(
                  onSave: () { Form.of(context).save(); close(); },
                  onCancel: () { Form.of(context).reset(); close(); },
                  child: new FormField<_Location>(
                    initialValue: item.value,
                    onSaved: (_Location result) { item.value = result; },
                    builder: (FormFieldState<_Location> field) {
                      return new Column(
                        mainAxisSize: MainAxisSize.min,
                        crossAxisAlignment: CrossAxisAlignment.start,
                        children: <Widget>[
                          new Row(
                            mainAxisSize: MainAxisSize.min,
                            children: <Widget>[
                              new Radio<_Location>(
                                value: _Location.Bahamas,
                                groupValue: field.value,
                                onChanged: field.didChange,
                              ),
                              const Text('Bahamas')
                            ]
                          ),
                          new Row(
                            mainAxisSize: MainAxisSize.min,
                            children: <Widget>[
                              new Radio<_Location>(
                                value: _Location.Barbados,
                                groupValue: field.value,
                                onChanged: field.didChange,
                              ),
                              const Text('Barbados')
                            ]
                          ),
                          new Row(
                            mainAxisSize: MainAxisSize.min,
                            children: <Widget>[
                              new Radio<_Location>(
                                value: _Location.Bermuda,
                                groupValue: field.value,
                                onChanged: field.didChange,
                              ),
                              const Text('Bermuda')
                            ]
                          )
                        ]
                      );
                    }
                  ),
                );
              }
            )
          );
        }
      ),
      new DemoItem<double>(
        name: 'Sun',
        value: 80.0,
        hint: 'Select sun level',
        valueToString: (double amount) => '${amount.round()}',
        builder: (DemoItem<double> item) {
          void close() {
            setState(() {
              item.isExpanded = false;
            });
          }

          return new Form(
            child: new Builder(
              builder: (BuildContext context) {
                return new CollapsibleBody(
                  onSave: () { Form.of(context).save(); close(); },
                  onCancel: () { Form.of(context).reset(); close(); },
                  child: new FormField<double>(
                    initialValue: item.value,
                    onSaved: (double value) { item.value = value; },
                    builder: (FormFieldState<double> field) {
                      return new Slider(
                        min: 0.0,
                        max: 100.0,
                        divisions: 5,
                        activeColor: Colors.orange[100 + (field.value * 5.0).round()],
                        label: '${field.value.round()}',
                        value: field.value,
                        onChanged: field.didChange,
                      );
                    },
                  ),
                );
              }
            )
          );
        }
      )
    ];
  }

  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      appBar: new AppBar(title: const Text('Expansion panels')),
      body: new SingleChildScrollView(
        child: new SafeArea(
          top: false,
          bottom: false,
          child: new Container(
            margin: const EdgeInsets.all(24.0),
            child: new ExpansionPanelList(
              expansionCallback: (int index, bool isExpanded) {
                setState(() {
                  _demoItems[index].isExpanded = !isExpanded;
                });
              },
              children: _demoItems.map((DemoItem<dynamic> item) {
                return new ExpansionPanel(
                  isExpanded: item.isExpanded,
                  headerBuilder: item.headerBuilder,
                  body: item.build()
                );
              }).toList()
            ),
          ),
        ),
      ),
    );
  }
}