examples/flutter_gallery/lib/demo/material/leave_behind_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:collection/collection.dart' show lowerBound;

import 'package:flutter/material.dart';
import 'package:flutter/semantics.dart';

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

enum LeaveBehindDemoAction {
  reset,
  horizontalSwipe,
  leftSwipe,
  rightSwipe
}

class LeaveBehindItem implements Comparable<LeaveBehindItem> {
  LeaveBehindItem({ this.index, this.name, this.subject, this.body });

  LeaveBehindItem.from(LeaveBehindItem item)
    : index = item.index, name = item.name, subject = item.subject, body = item.body;

  final int index;
  final String name;
  final String subject;
  final String body;

  @override
  int compareTo(LeaveBehindItem other) => index.compareTo(other.index);
}

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

  static const String routeName = '/material/leave-behind';

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

class LeaveBehindDemoState extends State<LeaveBehindDemo> {
  static final GlobalKey<ScaffoldState> _scaffoldKey = GlobalKey<ScaffoldState>();
  DismissDirection _dismissDirection = DismissDirection.horizontal;
  List<LeaveBehindItem> leaveBehindItems;

  void initListItems() {
    leaveBehindItems = List<LeaveBehindItem>.generate(16, (int index) {
      return LeaveBehindItem(
        index: index,
        name: 'Item $index Sender',
        subject: 'Subject: $index',
        body: "[$index] first line of the message's body..."
      );
    });
  }

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

  void handleDemoAction(LeaveBehindDemoAction action) {
    setState(() {
      switch (action) {
        case LeaveBehindDemoAction.reset:
          initListItems();
          break;
        case LeaveBehindDemoAction.horizontalSwipe:
          _dismissDirection = DismissDirection.horizontal;
          break;
        case LeaveBehindDemoAction.leftSwipe:
          _dismissDirection = DismissDirection.endToStart;
          break;
        case LeaveBehindDemoAction.rightSwipe:
          _dismissDirection = DismissDirection.startToEnd;
          break;
      }
    });
  }

  void handleUndo(LeaveBehindItem item) {
    final int insertionIndex = lowerBound(leaveBehindItems, item);
    setState(() {
      leaveBehindItems.insert(insertionIndex, item);
    });
  }

  void _handleArchive(LeaveBehindItem item) {
    setState(() {
      leaveBehindItems.remove(item);
    });
    _scaffoldKey.currentState.showSnackBar(SnackBar(
      content: Text('You archived item ${item.index}'),
      action: SnackBarAction(
        label: 'UNDO',
        onPressed: () { handleUndo(item); }
      )
    ));
  }

  void _handleDelete(LeaveBehindItem item) {
    setState(() {
      leaveBehindItems.remove(item);
    });
    _scaffoldKey.currentState.showSnackBar(SnackBar(
      content: Text('You deleted item ${item.index}'),
      action: SnackBarAction(
        label: 'UNDO',
        onPressed: () { handleUndo(item); }
      )
    ));
  }

  @override
  Widget build(BuildContext context) {
    Widget body;
    if (leaveBehindItems.isEmpty) {
      body = Center(
        child: RaisedButton(
          onPressed: () => handleDemoAction(LeaveBehindDemoAction.reset),
          child: const Text('Reset the list'),
        ),
      );
    } else {
      body = ListView(
        children: leaveBehindItems.map<Widget>((LeaveBehindItem item) {
          return _LeaveBehindListItem(
            item: item,
            onArchive: _handleArchive,
            onDelete: _handleDelete,
            dismissDirection: _dismissDirection,
          );
        }).toList()
      );
    }

    return Scaffold(
      key: _scaffoldKey,
      appBar: AppBar(
        title: const Text('Swipe to dismiss'),
        actions: <Widget>[
          MaterialDemoDocumentationButton(LeaveBehindDemo.routeName),
          PopupMenuButton<LeaveBehindDemoAction>(
            onSelected: handleDemoAction,
            itemBuilder: (BuildContext context) => <PopupMenuEntry<LeaveBehindDemoAction>>[
              const PopupMenuItem<LeaveBehindDemoAction>(
                value: LeaveBehindDemoAction.reset,
                child: Text('Reset the list')
              ),
              const PopupMenuDivider(),
              CheckedPopupMenuItem<LeaveBehindDemoAction>(
                value: LeaveBehindDemoAction.horizontalSwipe,
                checked: _dismissDirection == DismissDirection.horizontal,
                child: const Text('Horizontal swipe')
              ),
              CheckedPopupMenuItem<LeaveBehindDemoAction>(
                value: LeaveBehindDemoAction.leftSwipe,
                checked: _dismissDirection == DismissDirection.endToStart,
                child: const Text('Only swipe left')
              ),
              CheckedPopupMenuItem<LeaveBehindDemoAction>(
                value: LeaveBehindDemoAction.rightSwipe,
                checked: _dismissDirection == DismissDirection.startToEnd,
                child: const Text('Only swipe right')
              )
            ]
          )
        ]
      ),
      body: body,
    );
  }
}

class _LeaveBehindListItem extends StatelessWidget {
  const _LeaveBehindListItem({
    Key key,
    @required this.item,
    @required this.onArchive,
    @required this.onDelete,
    @required this.dismissDirection,
  }) : super(key: key);

  final LeaveBehindItem item;
  final DismissDirection dismissDirection;
  final void Function(LeaveBehindItem) onArchive;
  final void Function(LeaveBehindItem) onDelete;

  void _handleArchive() {
    onArchive(item);
  }

  void _handleDelete() {
    onDelete(item);
  }

  @override
  Widget build(BuildContext context) {
    final ThemeData theme = Theme.of(context);
    return Semantics(
      customSemanticsActions: <CustomSemanticsAction, VoidCallback>{
        const CustomSemanticsAction(label: 'Archive'): _handleArchive,
        const CustomSemanticsAction(label: 'Delete'): _handleDelete,
      },
      child: Dismissible(
        key: ObjectKey(item),
        direction: dismissDirection,
        onDismissed: (DismissDirection direction) {
          if (direction == DismissDirection.endToStart)
            _handleArchive();
          else
            _handleDelete();
        },
        background: Container(
          color: theme.primaryColor,
          child: const ListTile(
            leading: Icon(Icons.delete, color: Colors.white, size: 36.0)
          )
        ),
        secondaryBackground: Container(
          color: theme.primaryColor,
          child: const ListTile(
            trailing: Icon(Icons.archive, color: Colors.white, size: 36.0)
          )
        ),
        child: Container(
          decoration: BoxDecoration(
            color: theme.canvasColor,
            border: Border(bottom: BorderSide(color: theme.dividerColor))
          ),
          child: ListTile(
            title: Text(item.name),
            subtitle: Text('${item.subject}\n${item.body}'),
            isThreeLine: true
          ),
        ),
      ),
    );
  }
}