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

Question

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. Ju

Answer 1

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 {
  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: [
                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!