How to preserve widget states in flutter, when navigating using BottomNavigationBar?

Dart Problem Overview

I'm currently working on building a Flutter app that will preserve states when navigating from one screen, to another, and back again when utilizing BottomNavigationBar. Just like it works in the Spotify mobile application; if you have navigated down to a certain level in the navigation hierarchy on one of the main screens, changing screen via the bottom navigation bar, and later changing back to the old screen, will preserve where the user were in that hierarchy, including preservation of the state.

I have run my head against the wall, trying various different things without success.

I want to know how I can prevent the pages in pageChooser(), when toggled once the user taps the BottomNavigationBar item, from rebuilding themselves, and instead preserve the state they already found themselves in (the pages are all stateful Widgets).

import 'package:flutter/material.dart';
import './page_plan.dart';
import './page_profile.dart';
import './page_startup_namer.dart';

void main() => runApp(new Recipher());

class Recipher extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new Pages();
  }
}

class Pages extends StatefulWidget {
  @override
  createState() => new PagesState();
}

class PagesState extends State<Pages> {
  int pageIndex = 0;
  

  pageChooser() {
    switch (this.pageIndex) {
      case 0:
        return new ProfilePage();
        break;
      
      case 1:
        return new PlanPage();
        break;

      case 2:
        return new StartUpNamerPage(); 
        break;  
      
      default:
        return new Container(
          child: new Center(
            child: new Text(
              'No page found by page chooser.',
              style: new TextStyle(fontSize: 30.0)
              )
            ),
          );     
    }
  }

  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      home: new Scaffold(
        body: pageChooser(),
        bottomNavigationBar: new BottomNavigationBar(
          currentIndex: pageIndex,
          onTap: (int tappedIndex) { //Toggle pageChooser and rebuild state with the index that was tapped in bottom navbar
            setState(
              (){ this.pageIndex = tappedIndex; }
              ); 
            },
          items: <BottomNavigationBarItem>[
            new BottomNavigationBarItem(
              title: new Text('Profile'),
              icon: new Icon(Icons.account_box)
              ),
              new BottomNavigationBarItem(
                title: new Text('Plan'),
                icon: new Icon(Icons.calendar_today)
              ),
                new BottomNavigationBarItem(
                title: new Text('Startup'),
                icon: new Icon(Icons.alarm_on)
              )
            ],
          )
      )
    );
  }
}

Dart Solutions

Solution 1 - Dart

For keeping state in BottomNavigationBar, you can use IndexedStack

    @override
      Widget build(BuildContext context) {
        return Scaffold(
          bottomNavigationBar: BottomNavigationBar(
            onTap: (index) {
              setState(() {
                current_tab = index;
              });
            },
            currentIndex: current_tab,
            items: [
              BottomNavigationBarItem(
                ...
              ),
              BottomNavigationBarItem(
                ...
              ),
            ],
          ),
          body: IndexedStack(
            children: <Widget>[
              PageOne(),
              PageTwo(),
            ],
            index: current_tab,
          ),
        );
      }

Solution 2 - Dart

Late to the party, but I've got a simple solution. Use the PageView widget with the AutomaticKeepAliveClinetMixin.

The beauty of it that it doesn't load any tab until you click on it.

The page that includes the BottomNavigationBar:

var _selectedPageIndex;
List<Widget> _pages;
PageController _pageController;

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

  _selectedPageIndex = 0;
  _pages = [
    //The individual tabs.
  ];

  _pageController = PageController(initialPage: _selectedPageIndex);
}

@override
void dispose() {
  _pageController.dispose();

  super.dispose();
}

@override
Widget build(BuildContext context) {
  ...
    body: PageView(
      controller: _pageController,
      physics: NeverScrollableScrollPhysics(),
      children: _pages,
    ),
   bottomNavigationBar: BottomNavigationBar(
      ...
      currentIndex: _selectedPageIndex,
      onTap: (selectedPageIndex) {
        setState(() {
          _selectedPageIndex = selectedPageIndex;
          _pageController.jumpToPage(selectedPageIndex);
        });
      },
  ...
}

The individual tab:

class _HomeState extends State<Home> with AutomaticKeepAliveClientMixin<Home> {
  @override
  bool get wantKeepAlive => true;

  @override
  Widget build(BuildContext context) {
    //Notice the super-call here.
    super.build(context);
    ...
  }
}

I've made a video about it here.

Solution 3 - Dart

Use AutomaticKeepAliveClientMixin to force your tab content to not be disposed.

class PersistantTab extends StatefulWidget {
  @override
  _PersistantTabState createState() => _PersistantTabState();
}

class _PersistantTabState extends State<PersistantTab> with AutomaticKeepAliveClientMixin {
  @override
  Widget build(BuildContext context) {
    return Container();
  }

  // Setting to true will force the tab to never be disposed. This could be dangerous.
  @override
  bool get wantKeepAlive => true;
}

To make sure your tab does get disposed when it doesn't require to be persisted, make wantKeepAlive return a class variable. You must call updateKeepAlive() to update the keep alive status.

Example with dynamic keep alive:

// class PersistantTab extends StatefulWidget ...

class _PersistantTabState extends State<PersistantTab>
    with AutomaticKeepAliveClientMixin {
  bool keepAlive = false;

  @override
  void initState() {
    doAsyncStuff();
  }

  Future doAsyncStuff() async {
    keepAlive = true;
    updateKeepAlive();
    // Keeping alive...

    await Future.delayed(Duration(seconds: 10));

    keepAlive = false;
    updateKeepAlive();
    // Can be disposed whenever now.
  }

  @override
  bool get wantKeepAlive => keepAlive;

  @override
  Widget build(BuildContext context) {
    super.build();
    return Container();
  }
}

Solution 4 - Dart

Instead of returning new instance every time you run pageChooser, have one instance created and return the same.

Example:

class Pages extends StatefulWidget {
  @override
  createState() => new PagesState();
}

class PagesState extends State<Pages> {
  int pageIndex = 0;
  
  // Create all the pages once and return same instance when required
  final ProfilePage _profilePage = new ProfilePage(); 
  final PlanPage _planPage = new PlanPage();
  final StartUpNamerPage _startUpNamerPage = new StartUpNamerPage();


  Widget pageChooser() {
    switch (this.pageIndex) {
      case 0:
        return _profilePage;
        break;

      case 1:
        return _planPage;
        break;

      case 2:
        return _startUpNamerPage;
        break;

      default:
        return new Container(
          child: new Center(
              child: new Text(
                  'No page found by page chooser.',
                  style: new TextStyle(fontSize: 30.0)
              )
          ),
        );
    }
  }

  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
        home: new Scaffold(
            body: pageChooser(),
            bottomNavigationBar: new BottomNavigationBar(
              currentIndex: pageIndex,
              onTap: (int tappedIndex) { //Toggle pageChooser and rebuild state with the index that was tapped in bottom navbar
                setState(
                        (){ this.pageIndex = tappedIndex; }
                );
              },
              items: <BottomNavigationBarItem>[
                new BottomNavigationBarItem(
                    title: new Text('Profile'),
                    icon: new Icon(Icons.account_box)
                ),
                new BottomNavigationBarItem(
                    title: new Text('Plan'),
                    icon: new Icon(Icons.calendar_today)
                ),
                new BottomNavigationBarItem(
                    title: new Text('Startup'),
                    icon: new Icon(Icons.alarm_on)
                )
              ],
            )
        )
    );
  }
}

Or you can make use of widgets like PageView or Stack to achieve the same.

Hope that helps!

Solution 5 - Dart

Use “IndexedStack Widget” with “Bottom Navigation Bar Widget” to keep state of Screens/pages/Widget

Provide list of Widget to IndexedStack and index of widget you want to show because IndexedStack show single widget from list at one time.

final List<Widget> _children = [    FirstClass(),    SecondClass()  ];

Scaffold(
  body: IndexedStack(
    index: _selectedPage,
    children: _children,
  ),
  bottomNavigationBar: BottomNavigationBar(
    ........
    ........
  ), 
);

Solution 6 - Dart

The most convenient way I have found to do so is using PageStorage widget along with PageStorageBucket, which acts as a key value persistent layer.

Go through this article for a beautiful explanation -> https://steemit.com/utopian-io/@tensor/persisting-user-interface-state-and-building-bottom-navigation-bars-in-dart-s-flutter-framework

Solution 7 - Dart

Do not use IndexStack Widget, because it will instantiate all the tabs together, and suppose if all the tabs are making a network request then the callbacks will be messed up the last API calling tab will probably have the control of the callback.

Use AutomaticKeepAliveClientMixin for your stateful widget it is the simplest way to achieve it without instantiating all the tabs together.

My code had interfaces that were providing the respective responses to the calling tab I implemented it the following way.

Create your stateful widget

class FollowUpsScreen extends StatefulWidget {
  FollowUpsScreen();
        
  @override
  State<StatefulWidget> createState() {
    return FollowUpsScreenState();
  }
}
        
class FollowUpsScreenState extends State<FollowUpsScreen>
     with AutomaticKeepAliveClientMixin<FollowUpsScreen>
            implements OperationalControls {
    
  @override
  Widget build(BuildContext context) {
  //do not miss this line
    super.build(context);
    return .....;
  }

  @override
  bool get wantKeepAlive => true;
}

Solution 8 - Dart

proper way of preserving tabs state in bottom nav bar is by wrapping the whole tree with PageStorage() widget which takes a PageStorageBucket bucket as a required named parameter and for those tabs to which you want to preserve its state pas those respected widgets with PageStorageKey(<str_key>) then you are done !! you can see more details in this ans which i've answered few weeks back on one question : https://stackoverflow.com/a/68620032/11974847

there's other alternatives like IndexedWidget() but you should beware while using it , i've explained y we should be catious while using IndexedWidget() in the given link answer

good luck mate ..

Content Type	Original Author	Original Content on Stackoverflow
Question	ArtBelch	View Question on Stackoverflow
Solution 1 - Dart	Newaj	View Answer on Stackoverflow
Solution 2 - Dart	Tayan	View Answer on Stackoverflow
Solution 3 - Dart	Charles Crete	View Answer on Stackoverflow
Solution 4 - Dart	Hemanth Raj	View Answer on Stackoverflow
Solution 5 - Dart	Techalgoware	View Answer on Stackoverflow
Solution 6 - Dart	Anirudh Agarwal	View Answer on Stackoverflow
Solution 7 - Dart	Swapnil Kadam	View Answer on Stackoverflow
Solution 8 - Dart	Himmat rai	View Answer on Stackoverflow