repro of https://stackoverflow.com/questions/56874563/how-to-structure-app-state-so-all-dependent-widgets-update-when-state-changes

so_provider_and_future.dart

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

void main() => runApp(
      ChangeNotifierProvider<AppStateManager>.value(
        value: AppStateManager(),
        child: MyApp(),
      ),
    );

class AppStateManager extends ChangeNotifier {
  int _currentStudentIndex = 0;
  int get currentStudentIndex => _currentStudentIndex;

  set currentStudentIndex(int index) {
    _currentStudentIndex = index;
    print('new current student: $index');
    notifyListeners();
  }
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

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

class Student {
  final String name;

  Student.fromString(this.name);
}

Future<List<String>> getStudents() => Future.value(['John', 'Jane', 'Filip']);

class _MyHomePageState extends State<MyHomePage> {
  _MyHomePageState() {
    print('constructing homepage state');
    getCurrentStudent().then((student) => setState(() {
          print('setting current student to ${student.name}');
          _currentStudent = student;
        }));
  }

  Future<Student> getCurrentStudent() async {
    List<String> students = await getStudents();

    final AppStateManager stateManager = Provider.of<AppStateManager>(context);

    String currentStudent = students[stateManager.currentStudentIndex ?? 0];

    return Student.fromString(currentStudent);
  }

  Student _currentStudent;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text(
              'Student: ${_currentStudent?.name}',
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () => Navigator.push<void>(
            context,
            MaterialPageRoute(
                builder: (context) => Scaffold(
                      body: Center(
                        child: MaterialButton(
                          onPressed: () {
                            Provider.of<AppStateManager>(context)
                                .currentStudentIndex = 2;
                            Navigator.pop(context);
                          },
                          child: const Text('hi'),
                        ),
                      ),
                    ))),
        tooltip: 'Increment',
        child: Icon(Icons.add),
      ),
    );
  }
}

so_provider_and_future_fixed.dart

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

void main() => runApp(
      ChangeNotifierProvider<AppStateManager>.value(
        value: AppStateManager(),
        child: MyApp(),
      ),
    );

class AppStateManager extends ChangeNotifier {
  int _currentStudentIndex = 0;
  int get currentStudentIndex => _currentStudentIndex;

  set currentStudentIndex(int index) {
    _currentStudentIndex = index;
    print('new current student: $index');
    notifyListeners();
  }
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

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

class Student {
  final String name;

  Student.fromString(this.name);
}

Future<List<String>> getStudents() => Future.value(['John', 'Jane', 'Filip']);

class _MyHomePageState extends State<MyHomePage> {
  Future<Student> getCurrentStudent(int index) async {
    List<String> students = await getStudents();

    final AppStateManager stateManager = Provider.of<AppStateManager>(context);

    String currentStudent = students[stateManager.currentStudentIndex ?? 0];

    return Student.fromString(currentStudent);
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Consumer<AppStateManager>(
              builder: (context, manager, child) => FutureBuilder<Student>(
                future: getCurrentStudent(manager.currentStudentIndex),
                builder: (context, snapshot) {
                  if (!snapshot.hasData) {
                    return const CircularProgressIndicator();
                  }
                  return Text('Student: ${snapshot.data.name}');
                },
              ),
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () => Navigator.push<void>(
            context,
            MaterialPageRoute(
                builder: (context) => Scaffold(
                      body: Center(
                        child: MaterialButton(
                          onPressed: () {
                            Provider.of<AppStateManager>(context)
                                .currentStudentIndex = 2;
                            Navigator.pop(context);
                          },
                          child: const Text('hi'),
                        ),
                      ),
                    ))),
        tooltip: 'Increment',
        child: Icon(Icons.add),
      ),
    );
  }
}