Reputation: 53
I am using the Flutter BLOC library (https://pub.dev/packages/bloc) I know there is a way to "listen to" BLOC states changes (with the listen() function)
chatBloc.listen((chatState) async {
if (chatState is ChatStateInitialized) {
// do something
}
});
But is there a way to listen to BLOC events instead ? Just like I would do with a classical StreamController ? Thanks to all who will be willing to help :-)
Julien
Upvotes: 5
Views: 4557
Reputation: 448
Updated for version 7/8
If you need to listen only for one Bloc changes, you can override void onChange(Change<State> change)
inside the desired Bloc class.
enum CounterEvent { increment }
class CounterBloc extends Bloc<CounterEvent, int> {
CounterBloc() : super(0);
@override
Stream<int> mapEventToState(CounterEvent event) async* {
switch (event) {
case CounterEvent.increment:
yield state + 1;
break;
}
}
@override
void onChange(Change<int> change) {
print(change);
super.onChange(change);
}
}
If you need to listen changes globally on multiple Blocs, you can use the BlocObserver
class.
class SimpleBlocObserver extends BlocObserver {
@override
void onChange(BlocBase bloc, Change change) {
super.onChange(bloc, change);
print('${bloc.runtimeType} $change');
}
@override
void onTransition(Bloc bloc, Transition transition) {
super.onTransition(bloc, transition);
print('${bloc.runtimeType} $transition');
}
@override
void onError(BlocBase bloc, Object error, StackTrace stackTrace) {
print('${bloc.runtimeType} $error $stackTrace');
super.onError(bloc, error, stackTrace);
}
}
Then, you need to initialize it.
void main() {
Bloc.observer = SimpleBlocObserver();
CounterBloc()
..add(CounterEvent.increment)
..close();
}
More info on the Flutter Bloc library documentation.
Upvotes: 2
Reputation: 2259
Yes, you can listen to BLoC events by below code:
BlocSupervisor.delegate = MyBlocDelegate();
And your main.dart similar to below code:
void main() {
WidgetsFlutterBinding.ensureInitialized();
BlocSupervisor.delegate = MyBlocDelegate();
runApp(MyApp());
}
class MyApp extends StatelessWidget {
// This widget is the root of your application.
@override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Flutter Demo',
theme: ThemeData(
primarySwatch: Colors.blue,
),
home: BlocProvider<CounterBLoC>(
create: (ctx) => CounterBLoC(),
child: TestBlocWidget(),
),
);
}
}
Here is your bloc_delegate.dart for listen to events of BLoC:
import 'package:bloc/bloc.dart';
class MyBlocDelegate extends BlocDelegate {
@override
void onEvent(Bloc bloc, Object event) {
print(event);
super.onEvent(bloc, event);
}
@override
void onError(Bloc bloc, Object error, StackTrace stackTrace) {
print(error);
super.onError(bloc, error, stackTrace);
}
@override
void onTransition(Bloc bloc, Transition transition) {
print(transition);
super.onTransition(bloc, transition);
}
}
Upvotes: 3