Implementing Multiple Pages into a Single Page using Navigation and a Stack

Question

In Flutter, I want to make screens like with Fragment in android, in this my code i try to replace each screens into current screen like with Fragment.replecae in android, i used Hook and Provider and my code work fine when in click on buttons to switch between them but i can't implementing back stack, which means when i click on Back button on phone, my code should show latest screen which i stored into _backStack variable, each swtich between this screens i stored current screen index into the this variable.

how can i solve back from this stack in my sample code?

// Switch Between screens:
DashboardPage(), UserProfilePage(), SearchPage()
------------->   ------------->     ------------->

// When back from stack:
                      DashboardPage(), UserProfilePage(), SearchPage()
Exit from application <--------------  <----------------  <-----------

i used Hook and i want to implementing this action with this library features

import 'dart:async';

import 'package:flutter/material.dart';
import 'package:flutter_hooks/flutter_hooks.dart';
import 'package:provider/provider.dart';

void main() {
  WidgetsFlutterBinding.ensureInitialized();
  runApp(MultiProvider(providers: [
    Provider.value(value: StreamBackStackSupport()),
    StreamProvider<homePages>(
      create: (context) =>
          Provider.of<StreamBackStackSupport>(context, listen: false)
              .selectedPage,
    )
  ], child: StartupApplication()));
}

class StartupApplication extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'BackStack Support App',
      home: MainBodyApp(),
    );
  }
}

class MainBodyApp extends HookWidget {
  final List<Widget> _fragments = [
    DashboardPage(),
    UserProfilePage(),
    SearchPage()
  ];
  List<int> _backStack = [0];
  int _currentIndex = 0;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('BackStack Screen'),
      ),
      body: WillPopScope(
        // ignore: missing_return
        onWillPop: () {
          customPop(context);
        },
        child: Container(
          child: Column(
            children: <Widget>[
              Consumer<homePages>(
                builder: (context, selectedPage, child) {
                  _currentIndex = selectedPage != null ? selectedPage.index : 0;
                  _backStack.add(_currentIndex);
                  return Expanded(child: _fragments[_currentIndex]);
                },
              ),
              Container(
                width: double.infinity,
                height: 50.0,
                padding: const EdgeInsets.symmetric(horizontal: 15.0),
                color: Colors.indigo[400],
                child: Row(
                  mainAxisAlignment: MainAxisAlignment.spaceBetween,
                  crossAxisAlignment: CrossAxisAlignment.center,
                  children: <Widget>[
                    RaisedButton(
                      onPressed: () => Provider.of<StreamBackStackSupport>(
                              context,
                              listen: false)
                          .switchBetweenPages(homePages.screenDashboard),
                      child: Text('Dashboard'),
                    ),
                    RaisedButton(
                      onPressed: () => Provider.of<StreamBackStackSupport>(
                              context,
                              listen: false)
                          .switchBetweenPages(homePages.screenProfile),
                      child: Text('Profile'),
                    ),
                    RaisedButton(
                      onPressed: () => Provider.of<StreamBackStackSupport>(
                              context,
                              listen: false)
                          .switchBetweenPages(homePages.screenSearch),
                      child: Text('Search'),
                    ),
                  ],
                ),
              ),
            ],
          ),
        ),
      ),
    );
  }

  void navigateBack(int index) {
    useState(() => _currentIndex = index);
  }

  void customPop(BuildContext context) {
    if (_backStack.length - 1 > 0) {
      navigateBack(_backStack[_backStack.length - 1]);
    } else {
      _backStack.removeAt(_backStack.length - 1);
      Provider.of<StreamBackStackSupport>(context, listen: false)
          .switchBetweenPages(homePages.values[_backStack.length - 1]);
      Navigator.pop(context);
    }
  }
}

class UserProfilePage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Container(
      alignment: Alignment.center,
      child: Text(' screenProfile ...'),
    );
  }
}

class DashboardPage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Container(
      alignment: Alignment.center,
      child: Text(' screenDashboard ...'),
    );
  }
}

class SearchPage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Container(
      alignment: Alignment.center,
      child: Text(' screenSearch ...'),
    );
  }
}

enum homePages { screenDashboard, screenProfile, screenSearch }

class StreamBackStackSupport {
  final StreamController<homePages> _homePages = StreamController<homePages>();

  Stream<homePages> get selectedPage => _homePages.stream;

  void switchBetweenPages(homePages selectedPage) {
    _homePages.add(homePages.values[selectedPage.index]);
  }

  void close() {
    _homePages.close();
  }
}

Answer 1

TL;DR

The full code is at the end.

Use Navigator instead

You should approach this problem differently. I could present you with a solution that would work with your approach, however, I think that you should instead solve this by implementing a custom Navigator as this is a built-in solution in Flutter.

---

When you are using a Navigator, you do not need any of your stream-based management, i.e. you can remove StreamBackStackSupport entirely.

Now, you insert a Navigator widget where you had your Consumer before:

children: <Widget>[
  Expanded(
    child: Navigator(
      ...
    ),
  ),
  Container(...), // Your bottom bar..
]

The navigator manages its routes using strings, which means that we will need to have a way to convert your enum (which I renamed to Page) to Strings. We can use describeEnum for that and put that into an extension:

enum Page { screenDashboard, screenProfile, screenSearch }

extension on Page {
  String get route => describeEnum(this);
}

Now, you can get the string representation of a page using e.g. Page.screenDashboard.route.

Furthermore, you want to map your actual pages to your fragment widgets, which you can do like this:

class MainBodyApp extends HookWidget {
  final Map<Page, Widget> _fragments = {
    Page.screenDashboard: DashboardPage(),
    Page.screenProfile: UserProfilePage(),
    Page.screenSearch: SearchPage(),
  };
  ...

To access the Navigator, we need to have a GlobalKey. Usually we would have a StatefulWidget and manage the GlobalKey like that. Since you want to use flutter_hooks, I opted to use a GlobalObjectKey instead:

  @override
  Widget build(BuildContext context) {
    final navigatorKey = GlobalObjectKey<NavigatorState>(context);
  ...

Now, you can use navigatorKey.currentState anywhere in your widget to access this custom navigator. The full Navigator setup looks like this:

Navigator(
  key: navigatorKey,
  initialRoute: Page.screenDashboard.route,
  onGenerateRoute: (settings) {
    final pageName = settings.name;

    final page = _fragments.keys.firstWhere((element) => describeEnum(element) == pageName);

    return MaterialPageRoute(settings: settings, builder: (context) => _fragments[page]);
  },
)

As you can see, we pass the navigatorKey created before and define an initialRoute, making use of the route extension we created. In onGenerateRoute, we find the Page enum entry corresponding to the route name (a String) and then return a MaterialPageRoute with the appropriate _fragments entry.

To push a new route, you simply use the navigatorKey and pushNamed:

onPressed: () => navigatorKey.currentState.pushNamed(Page.screenDashboard.route),

Back button

We also need to customly call pop on our custom navigator. For this purpose, a WillPopScope is needed:

WillPopScope(
  onWillPop: () async {
    if (navigatorKey.currentState.canPop()) {
      navigatorKey.currentState.pop();
      return false;
    }

    return true;
  },
  child: ..,
)

Access the custom navigator inside of the nested pages

In any page that is passed to onGenerateRoute, i.e. in any of your "fragments", you can just call Navigator.of(context) instead of using the global key. This is possible because these routes are children of the custom navigator and thus, the BuildContext contains that custom navigator.

For example:

// In SearchPage
Navigator.of(context).pushNamed(Page.screenProfile.route);

Default navigator

You might be wondering how you can get access to the MaterialApp root navigator now, e.g. to push a new full screen route. You can use findRootAncestorStateOfType for that:

context.findRootAncestorStateOfType<NavigatorState>().push(..);

or simply

Navigator.of(context, rootNavigator: true).push(..);

---

Here is the full code:

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

void main() {
  runApp(StartupApplication());
}

enum Page { screenDashboard, screenProfile, screenSearch }

extension on Page {
  String get route => describeEnum(this);
}

class StartupApplication extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'BackStack Support App',
      home: MainBodyApp(),
    );
  }
}

class MainBodyApp extends HookWidget {
  final Map<Page, Widget> _fragments = {
    Page.screenDashboard: DashboardPage(),
    Page.screenProfile: UserProfilePage(),
    Page.screenSearch: SearchPage(),
  };

  @override
  Widget build(BuildContext context) {
    final navigatorKey = GlobalObjectKey<NavigatorState>(context);

    return WillPopScope(
      onWillPop: () async {
        if (navigatorKey.currentState.canPop()) {
          navigatorKey.currentState.pop();
          return false;
        }

        return true;
      },
      child: Scaffold(
        appBar: AppBar(
          title: Text('BackStack Screen'),
        ),
        body: Container(
          child: Column(
            children: <Widget>[
              Expanded(
                child: Navigator(
                  key: navigatorKey,
                  initialRoute: Page.screenDashboard.route,
                  onGenerateRoute: (settings) {
                    final pageName = settings.name;

                    final page = _fragments.keys.firstWhere(
                        (element) => describeEnum(element) == pageName);

                    return MaterialPageRoute(settings: settings,
                        builder: (context) => _fragments[page]);
                  },
                ),
              ),
              Container(
                width: double.infinity,
                height: 50.0,
                padding: const EdgeInsets.symmetric(horizontal: 15.0),
                color: Colors.indigo[400],
                child: Row(
                  mainAxisAlignment: MainAxisAlignment.spaceBetween,
                  crossAxisAlignment: CrossAxisAlignment.center,
                  children: <Widget>[
                    RaisedButton(
                      onPressed: () => navigatorKey.currentState
                          .pushNamed(Page.screenDashboard.route),
                      child: Text('Dashboard'),
                    ),
                    RaisedButton(
                      onPressed: () => navigatorKey.currentState
                          .pushNamed(Page.screenProfile.route),
                      child: Text('Profile'),
                    ),
                    RaisedButton(
                      onPressed: () => navigatorKey.currentState
                          .pushNamed(Page.screenSearch.route),
                      child: Text('Search'),
                    ),
                  ],
                ),
              ),
            ],
          ),
        ),
      ),
    );
  }
}

class UserProfilePage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Container(
      alignment: Alignment.center,
      child: Text(' screenProfile ...'),
    );
  }
}

class DashboardPage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Container(
      alignment: Alignment.center,
      child: Text(' screenDashboard ...'),
    );
  }
}

class SearchPage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Container(
      alignment: Alignment.center,
      child: Text(' screenSearch ...'),
    );
  }
}