Share bloc across different routes

Question

I'm trying to share same bloc across two routes. But when I come back from second route the bloc get automatically disposed so in the first route I find myself with all the stream closed.

For example this is the first route (HomePage) where I instantiate the bloc, download a list from api and show it in the build method.

class HomePage extends StatefulWidget {
  @override
  State<StatefulWidget> createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> {


  GroupsBloc _groupBloc;

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

  @override
  void didChangeDependencies(){
    super.didChangeDependencies();
    _groupBloc = GroupsBloc();
    _groupBloc.getAll();
  }

  @override
  void dispose(){
    _groupBloc.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
   ...
  }
}

Then I navigate to a second screen where I can add an item to the list.

  _onAddGroupPress(){
    Navigator.of(context).push(new MaterialPageRoute(
        builder: (BuildContext context) => BlocProvider<GroupsBloc>(bloc: _groupBloc, child: GroupPage()),
        fullscreenDialog: true
      ),
    );
  }

In the second screen I retrieve the bloc and I use it to add an item, then I go back to Home Page.

class GroupPage extends StatefulWidget {

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

class _GroupPageState extends State<GroupPage> {

  FormBloc _formBloc; //another bloc
  GroupsBloc _groupBloc;


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

  @override
  void didChangeDependencies(){
    super.didChangeDependencies();
    _formBloc = FormBloc();
    _groupBloc = BlocProvider.of<GroupsBloc>(context); //retrieve of the bloc 
  }

  @override
  void dispose() {
    _formBloc?.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
   ...
  }

In the dispose method of the second screen I dispose only _formBloc bloc but _groupBloc gets disposed too, so when I come back in the first page I found myself with _groupBloc disposed and all it's stream closes.

I tought of passing the bloc to the second screen as a props but I don't know if it's the right way to do this.

Answer 1

It obviously depends on the scope of your Bloc, but there is nothing preventing you from sharing the same instance throughout your whole app.

ie. simply wrap your whole MaterialApp inside BlocProvider<GroupsBloc>(bloc: _groupBloc, child: MaterialApp( ... ))

if "groups" are not global to your app, you should probably just pass the bloc along to the second widget.