Recreating Android Single-Top Activity behaviour with Flutter Route's - by Simon Lightfoot

single_top.dart

// MIT License
//
// Copyright (c) 2019 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 'package:flutter/material.dart';

void main() => runApp(ExampleApp());

class ExampleApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      theme: ThemeData.dark(),
      onGenerateRoute: (RouteSettings settings) {
        if (settings.name == Navigator.defaultRouteName) {
          return Activity<int>(
            builder: (BuildContext context) => TestScreen(index: 0),
            intent: 0,
          );
        }
        return null;
      },
    );
  }
}

class TestScreen extends StatefulWidget {
  const TestScreen({
    Key key,
    @required this.index,
  }) : super(key: key);

  final int index;

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

class _TestScreenState extends State<TestScreen> with SingleTopStateMixin<TestScreen, int> {
  int _index;

  @override
  void initState() {
    super.initState();
    _index = widget.index;
  }

  @override
  void onNewIntent(int intent) {
    setState(() => _index = intent);
  }

  @override
  Widget build(BuildContext context) {
    final next = _index + 1;
    return Material(
      child: Container(
        color: Colors.primaries[_index % Colors.primaries.length],
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text(
              'Page ${_index}',
              style: TextStyle(fontSize: 32.0),
            ),
            Padding(
              padding: const EdgeInsets.all(16.0),
              child: Text(Activity.isSingleTop(context) ? 'Launched with Single-Top' : ''),
            ),
            RaisedButton(
              onPressed: () {
                Activity.startActivity<int>(
                  context,
                  builder: (BuildContext context) => TestScreen(index: next),
                  intent: next,
                );
              },
              child: Text('Next'),
            ),
            RaisedButton(
              onPressed: () {
                Activity.startActivity<int>(
                  context,
                  builder: (BuildContext context) => TestScreen(index: next),
                  intent: next,
                  singleTop: true,
                );
              },
              child: Text('Single Top'),
            ),
            RaisedButton(
              onPressed: () {
                Activity.startActivity<int>(
                  context,
                  builder: (BuildContext context) => TestScreen(index: next),
                  intent: next,
                  singleTop: true,
                  clearTop: true,
                );
              },
              child: Text('Single Top with Clear'),
            ),
          ],
        ),
      ),
    );
  }
}

/// Activity style route with single-top support
class Activity<I> extends MaterialPageRoute {
  static Activity _last;

  static Activity<I> of<I>(BuildContext context) {
    final activity = ModalRoute.of(context);
    return (activity is Activity) ? activity : null;
  }

  static bool isSingleTop<I>(BuildContext context) {
    final activity = of<I>(context);
    return (activity != null) ? activity.singleTop : false;
  }

  static void startActivity<I>(
    BuildContext context, {
    @required WidgetBuilder builder,
    @required I intent,
    RouteSettings settings,
    bool maintainState = true,
    bool fullscreenDialog = false,
    bool singleTop = false,
    bool clearTop = false,
  }) {
    final activity = Activity.of<I>(context);
    if (singleTop) {
      if (activity != null && activity.singleTop) {
        activity.onNewIntent(intent);
        return;
      } else if (_last != null && clearTop) {
        Navigator.of(context).popUntil((route) => route == _last);
        _last.onNewIntent(intent);
        return;
      }
    }
    Navigator.of(context).push(Activity<I>(
      builder: builder,
      intent: intent,
      settings: settings,
      maintainState: maintainState,
      fullscreenDialog: fullscreenDialog,
      singleTop: singleTop,
    ));
  }

  Activity({
    @required WidgetBuilder builder,
    @required I intent,
    RouteSettings settings,
    bool maintainState = true,
    bool fullscreenDialog = false,
    this.singleTop = false,
  })  : _intent = ValueNotifier<I>(intent),
        super(
          builder: builder,
          settings: settings,
          maintainState: maintainState,
          fullscreenDialog: fullscreenDialog,
        );

  final ValueNotifier<I> _intent;
  final bool singleTop;

  I get intent => _intent.value;

  void onNewIntent(I intent) => _intent.value = intent;

  @override
  TickerFuture didPush() {
    if (singleTop) _last = this;
    return super.didPush();
  }

  @override
  bool didPop(result) {
    if (_last == this) _last = null;
    return super.didPop(result);
  }
}

@optionalTypeArgs
mixin SingleTopStateMixin<T extends StatefulWidget, I> on State<T> {
  ValueNotifier<I> _intent;

  I get intent => _intent.value;

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

    final activity = Activity.of(context);
    if (activity != null) {
      if (_intent != activity._intent) {
        _intent?.removeListener(_onIntentChanged);
        _intent = activity._intent;
        _intent.addListener(_onIntentChanged);
      }
    }
  }

  void _onIntentChanged() => onNewIntent(_intent.value);

  void onNewIntent(covariant I intent);

  @override
  void dispose() {
    _intent?.removeListener(_onIntentChanged);
    _intent = null;

    super.dispose();
  }
}