Is there a way to trigger a BlocListener just after its initialization? - flutter

Question

I'm working with Bloc and Hydrated Bloc and at some point in my app I want to store a boolean variable "firstTime" in a Hydrated Bloc to know if it's the first time my user is using the app. If it is the case, I redirect the user to a on-boarding page (called IntroPage), and if not, the login screen is displayed.
I use a BlocListener to listen to the changes of "firstTime", so once my user has finished navigating the on-boarding page, it redirects to the login screen.
#override
Widget build(BuildContext context) {
return MaterialApp(
...
builder: (context, child) {
return BlocListener<UserPreferencesBloc, UserPreferencesState>(
listener: (context, state) {
if (state.firstTime) {
_navigator.pushAndRemoveUntil<void>(
IntroPage.route(),
(route) => false,
);
}
},
child: child,
);
},
onGenerateRoute: (_) => SplashPage.route(),
);
}
The main problem is that if there's no change in the state of the Bloc, it does not fire the BlocListener part. The user never access the IntroPage.
Is there a way to make it so I can get into that listener just after its initialization, even without any change in the state of the Bloc ? Or is there another way to do that (that doesn't involve the use of Shared Preferences or other packages) ?
Edit : Here is the code for the Bloc :
class UserPreferencesBloc
extends HydratedBloc<UserPreferencesEvent, UserPreferencesState> {
UserPreferencesBloc() : super(const UserPreferencesState()) {
on<UserPreferencesFirstTimed>(_onFirstTime);
}
void _onFirstTime(
UserPreferencesFirstTimed event,
Emitter<UserPreferencesState> emit,
) async {
emit(state.copyWith(firstTime: event.firstTime));
}
#override
UserPreferencesState? fromJson(Map<String, dynamic> json) {
return UserPreferencesState(firstTime: json['firstTime'] as bool);
}
#override
Map<String, dynamic>? toJson(UserPreferencesState state) => {
'firstTime': state.firstTime,
};
}
And here is the state :
part of 'user_preferences_bloc.dart';
class UserPreferencesState extends Equatable {
const UserPreferencesState({
this.firstTime = true,
});
final bool firstTime;
UserPreferencesState copyWith({
bool? firstTime,
}) {
return UserPreferencesState(
firstTime: firstTime ?? this.firstTime,
);
}
#override
List<Object> get props => [firstTime];
}
And the Bloc is initialized in the app.dart file, at the start of the application :
class App extends StatelessWidget {
const App({
Key? key,
}) : super(key: key);
#override
Widget build(BuildContext context) {
return MultiRepositoryProvider(
providers: ... //not shown in this piece of code
child: MultiBlocProvider(
providers: [
...
BlocProvider(create: (_) => UserPreferencesBloc())
],
child: AppView(),
),
);
}
}

Answer 1

It is by design so that BlocListener is only triggered once per state change.
But there are of course ways to do what you are after. If you'd show how you provide/create the bloc and also the definition of the state it could help...
But you could for instance let firstTime be nullable and use the cascade notion operator (..) when creating the bloc to immediately call a method in the bloc that sets the value of firstTime to true/false after initialization.
Edit:
Obviously hard from here to write all the changes you'd have to make, but here is the main idea:
Change: final bool firstTime; to bool? firstTime; and handle the null cases where applicable.
On creation, change:
BlocProvider(create: (_) => UserPreferencesBloc())
to:
BlocProvider(create: (_) => UserPreferencesBloc()..onFirstTime())
Write the method onFirstTime() something like this:
void onFirstTime() async {
emit(state.copyWith(firstTime: state.firstTime ?? true));
}
And remove the on<UserPreferencesFirstTimed>(_onFirstTime); part as well as this.firstTime = true,