Flutter ReorderableList

import 'package:flutter/foundation.dart';
import 'package:flutter/material.dart';
import 'package:flutter/rendering.dart';

import '../../gallery/demo.dart';

enum _ReorderableListType {
  /// A list tile that contains a [CircleAvatar].
  horizontalAvatar,

  /// A list tile that contains a [CircleAvatar].
  verticalAvatar,

  /// A list tile that contains three lines of text and a checkbox.
  threeLine,
}

class ReorderableListDemo extends StatefulWidget {
  const ReorderableListDemo({ Key key }) : super(key: key);

  static const String routeName = '/material/reorderable-list';

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

class _ListItem {
  _ListItem(this.value, this.checkState);

  final String value;

  bool checkState;
}

class _ListDemoState extends State<ReorderableListDemo> {
  static final GlobalKey<ScaffoldState> scaffoldKey = GlobalKey<ScaffoldState>();

  PersistentBottomSheetController<void> _bottomSheet;
  _ReorderableListType _itemType = _ReorderableListType.threeLine;
  bool _reverse = false;
  bool _reverseSort = false;
  final List<_ListItem> _items = <String>[
    'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N',
  ].map<_ListItem>((String item) => _ListItem(item, false)).toList();

  void changeItemType(_ReorderableListType type) {
    setState(() {
      _itemType = type;
    });
    // Rebuild the bottom sheet to reflect the selected list view.
    _bottomSheet?.setState(() {
      // Trigger a rebuild.
    });
    // Close the bottom sheet to give the user a clear view of the list.
    _bottomSheet?.close();
  }

  void changeReverse(bool newValue) {
    setState(() {
      _reverse = newValue;
    });
    // Rebuild the bottom sheet to reflect the selected list view.
    _bottomSheet?.setState(() {
      // Trigger a rebuild.
    });
    // Close the bottom sheet to give the user a clear view of the list.
    _bottomSheet?.close();
  }

  void _showConfigurationSheet() {
    setState(() {
      _bottomSheet = scaffoldKey.currentState.showBottomSheet<void>((BuildContext bottomSheetContext) {
        return DecoratedBox(
          decoration: const BoxDecoration(
            border: Border(top: BorderSide(color: Colors.black26)),
          ),
          child: ListView(
            shrinkWrap: true,
            primary: false,
            children: <Widget>[
              CheckboxListTile(
                dense: true,
                title: const Text('Reverse'),
                value: _reverse,
                onChanged: changeReverse,
              ),
              RadioListTile<_ReorderableListType>(
                dense: true,
                title: const Text('Horizontal Avatars'),
                value: _ReorderableListType.horizontalAvatar,
                groupValue: _itemType,
                onChanged: changeItemType,
              ),
              RadioListTile<_ReorderableListType>(
                dense: true,
                title: const Text('Vertical Avatars'),
                value: _ReorderableListType.verticalAvatar,
                groupValue: _itemType,
                onChanged: changeItemType,
              ),
              RadioListTile<_ReorderableListType>(
                dense: true,
                title: const Text('Three-line'),
                value: _ReorderableListType.threeLine,
                groupValue: _itemType,
                onChanged: changeItemType,
              ),
            ],
          ),
        );
      });

      // Garbage collect the bottom sheet when it closes.
      _bottomSheet.closed.whenComplete(() {
        if (mounted) {
          setState(() {
            _bottomSheet = null;
          });
        }
      });
    });
  }

  Widget buildListTile(_ListItem item) {
    const Widget secondary = Text(
      'Even more additional list item information appears on line three.',
    );
    Widget listTile;
    switch (_itemType) {
      case _ReorderableListType.threeLine:
        listTile = CheckboxListTile(
          key: Key(item.value),
          isThreeLine: true,
          value: item.checkState ?? false,
          onChanged: (bool newValue) {
            setState(() {
              item.checkState = newValue;
            });
          },
          title: Text('This item represents ${item.value}.'),
          subtitle: secondary,
          secondary: const Icon(Icons.drag_handle),
        );
        break;
      case _ReorderableListType.horizontalAvatar:
      case _ReorderableListType.verticalAvatar:
        listTile = Container(
          key: Key(item.value),
          height: 100.0,
          width: 100.0,
          child: CircleAvatar(child: Text(item.value),
            backgroundColor: Colors.green,
          ),
        );
        break;
    }

    return listTile;
  }

  void _onReorder(int oldIndex, int newIndex) {
    setState(() {
      if (newIndex > oldIndex) {
        newIndex -= 1;
      }
      final _ListItem item = _items.removeAt(oldIndex);
      _items.insert(newIndex, item);
    });
  }


  @override
  Widget build(BuildContext context) {
    return Scaffold(
      key: scaffoldKey,
      appBar: AppBar(
        title: const Text('Reorderable list'),
        actions: <Widget>[
          MaterialDemoDocumentationButton(ReorderableListDemo.routeName),
          IconButton(
            icon: const Icon(Icons.sort_by_alpha),
            tooltip: 'Sort',
            onPressed: () {
              setState(() {
                _reverseSort = !_reverseSort;
                _items.sort((_ListItem a, _ListItem b) => _reverseSort ? b.value.compareTo(a.value) : a.value.compareTo(b.value));
              });
            },
          ),
          IconButton(
            icon: Icon(
              Theme.of(context).platform == TargetPlatform.iOS
                  ? Icons.more_horiz
                  : Icons.more_vert,
            ),
            tooltip: 'Show menu',
            onPressed: _bottomSheet == null ? _showConfigurationSheet : null,
          ),
        ],
      ),
      body: Scrollbar(
        child: ReorderableListView(
          header: _itemType != _ReorderableListType.threeLine
              ? Padding(
                  padding: const EdgeInsets.all(8.0),
                  child: Text('Header of the list', style: Theme.of(context).textTheme.headline))
              : null,
          onReorder: _onReorder,
          reverse: _reverse,
          scrollDirection: _itemType == _ReorderableListType.horizontalAvatar ? Axis.horizontal : Axis.vertical,
          padding: const EdgeInsets.symmetric(vertical: 8.0),
          children: _items.map<Widget>(buildListTile).toList(),
        ),
      ),
    );
  }
}