Flutter application freezes after notifyListeners - flutter

Question

I'm trying to write a simple Flutter app using the Google Maps plugin. I need to use multiple BLoC/ChangeNotifier objects in order to manage the object shown on-screen.
The issue comes out when I call notifyListeners() on a ChangeNotifier. The method which calls notifyListeners() completes its execution, and then the app freezes completely (no widget update, unable to interact with existing widgets).
I've tried to understand where's the problem: the only thing I understood is that it works fine while CompaniesData (which is the ChangeNotifier that causes the problem) is empty.
class CompaniesData extends ChangeNotifier {
Map<MarkerId, Company> _companiesMap;
set companies(Set<Company> companies) {
_companiesMap = companies != null
? Map.fromIterable(
companies,
key: (company) => MarkerId(company.id.toString()),
value: (company) => company,
)
: null;
notifyListeners();
;
}
bool get available => _companiesMap != null;
Company companyWithId(MarkerId id) => available ? _companiesMap[id] : null;
Map<MarkerId, Company> get companiesIfAvailable =>
available ? _companiesMap : Map();
Iterable<Company> companiesFromIds(BuildContext context, Set<int> ids) {
Set<int> idsCopy = Set.from(ids);
return companiesIfAvailable.entries
.where((entry) => idsCopy.remove(entry.value.id))
.map<Company>((entry) => entry.value);
}
}
#override
Widget build(BuildContext context) {
return Stack(
children: <Widget>[
Consumer<CompaniesData>(
builder: (context, data, child) {
return BlocBuilder(
bloc: BlocProvider.of<ShownCompaniesBloc>(context),
builder: (context, shownCompaniesState) {
return BlocBuilder(
bloc: BlocProvider.of<FavoriteCompaniesBloc>(context),
builder: (context, favoriteCompaniesState) {
return BlocBuilder(
bloc: BlocProvider.of<MapPropertiesBloc>(context),
builder: (context, mapPropertiesState) {
CompaniesData data =
Provider.of<CompaniesData>(context, listen: false);
// ...
As you can see, the build method contains multiple nested BLoC/Consumer objects.
#override
void initState() {
_fetchCompanies();
super.initState();
}
void _fetchCompanies() {
findUser().then((location) {
Set<Company> companies = Set.from([Company.fake()]);
// CompaniesData.companies is a setter, which calls
// notifyListeners
_companiesData.companies = companies;
});
}
I don't get error messages, exception, my app simply dies after the end of the execution of the callback given to findUser().then().
EDIT:
I changed the code a little bit, and I figured out that the problem isn't notifyListeners (or at least it isn't now).
final Completer<Map<MarkerId, Company>> _companiesData = Completer();
_AeroMainViewState() {
findUser()
.then(_fetchCompanies)
.then((companies) => _companiesData.complete(Map.fromIterable(
companies,
key: (company) => MarkerId(company.id.toString()),
value: (company) => company,
)));
}
Future<Set<Company>> _fetchCompanies(LatLng location) async =>
Set.from([Company.fake()]);
// ...
child: FutureBuilder<Map<MarkerId, Company>>(
future: _companiesData.future,
builder: (context, snapshot) {
// this builder function isn't called at all
// when the Completer _companiesData is completed
if (snapshot.connectionState == ConnectionState.done) {
return Provider<Map<MarkerId, Company>>.value(
value: snapshot.data,
child: // ...
} else {
return Center(child: CircularProgressIndicator());
}
}),
// ...
Removing the ChangeNotifier doesn't fix the issue.

Answer 1

I post my error for future reference. I was doing this in a class:
static Stream<Obj1> stream() async* {
while (true) {
yield Obj1();
}
}
_subscription = Obj1.stream().listen((event) {
// do something...
}
Since the Stream contains potentially an infinite number of objects, the subscription to that stream was blocking the main (and only) thread.