Flutter bloc state is not emitting or updating. Method mapEventToState is never called - flutter

Question

The following code was working before null safety with flutter_bloc 4.0.1 but after null safety migration the state is not updating / emitting / broadcasting as expected with flutter_bloc 7.3.3.
The below _reactToState and mapEventToState methods are never called. How can I fix it?
Splash Screen
class SplashScreen extends StatefulWidget {
final Strapper strapper;
final Service? service;
SplashScreen(this.strapper, this.service);
#override
State<StatefulWidget> createState() => _SplashScreenState();
}
class _SplashScreenState extends State<SplashScreen> {
SplashBloc? _splashBloc;
#override
void didChangeDependencies() {
super.didChangeDependencies();
if (_splashBloc == null) {
_splashBloc = SplashBloc(widget.strapper, widget.service);
_splashBloc!.stream.listen(_reactToState);
}
}
#override
dispose() {
_splashBloc?.close();
_splashBloc = null;
super.dispose();
}
#override
Widget build(BuildContext context) {
return BlocProvider<SplashBloc>(
create: (context) => _splashBloc!,
child: BlocBuilder<SplashBloc, SplashBlocState>(
builder: (context, state) => Container(
child: Stack(
children: <Widget>[
LogoPanel(
_showWidgetForState(state),
),
],
),
),
),
);
}
void _reactToState(SplashBlocState state) {
if (state is InitializingSplashBlocState) {
if (widget.logOut) {
_splashBloc!.add(LogoutSplashBlocEvent());
} else {
_splashBloc!.add(CInitializationSplashBlocEvent());
}
} else if (state is AuthSuccessSplashBlocState) {
App.navigateToSomewhere(context, state.isNewUser);
}
}
Widget _showWidgetForState(SplashBlocState state) {
if (state is InitializingSplashBlocState) {
return _getProgressIndicator();
} else if (state is ChooseSomethingSplashBlockState ) {
return _showSignInWidget();
}
}
}
Splash Bloc
class SplashBloc extends Bloc<SplashBlocEvent, SplashBlocState> {
final Strapper? strapper;
final Service? service;
SplashBloc(this.strapper, this.service) : super(InitializingSplashBlocState());
#override
Stream<SplashBlocState> mapEventToState(event) async* {
if (event is CInitializationSplashBlocEvent) {
await strapper!.run();
}
bool chooseSomething = !service!.hasSomeSelection;
if (chooseSomething) {
yield ChooseSomethingSplashBlockState();
} else if (event is RAuthSplashBlocEvent) {
yield AuthSplashBlocState();
var authState = await _run();
yield authState;
}
}
Future<SplashBlocState> _run() async {
// Do something
}
}
Splash Bloc Event
abstract class SplashBlocEvent extends Equatable {
const SplashBlocEvent();
#override
List<Object> get props => [];
}
class CInitializationSplashBlocEvent extends SplashBlocEvent {}
class RAuthSplashBlocEvent extends SplashBlocEvent {}
Splash Bloc State
abstract class SplashBlocState extends Equatable {
const SplashBlocState();
#override
List<Object> get props => [];
}
class InitializingSplashBlocState extends SplashBlocState {}
class AuthSplashBlocState extends SplashBlocState {}
class ChooseSomethingSplashBlockState extends SplashBlocState {}
class AuthSuccessSplashBlocState extends SplashBlocState {
final CurrentUser? user;
final bool isNewUser;
AuthSuccessSplashBlocState(this.user, this.isNewUser);
}

Answer 1

As per the documentation:
In v6.0.0, the above snippet does not output the initial state and only outputs subsequent state changes. The previous behavior can be achieved with the following:
final bloc = MyBloc();
print(bloc.state);
bloc.listen(print);
So I changed my code in the Splash screen as following:
#override
void didChangeDependencies() {
super.didChangeDependencies();
if (_splashBloc == null) {
_splashBloc = SplashBloc(widget.strapper, widget.service);
_reactToState(_splashBloc!.state); // Added this line
_splashBloc!.stream.listen(_reactToState);
}
}
And that's it. It worked!
_reactToState and mapEventToState are definitely being called.

Answer 2

when you use Streamcontrollers it greatly simplifies state. I build a bloc code to manage state. The materialapp child is the splashWidget whose job is to render the hour, minute, second from bloc code emitting Time state. If the user clicks the splash screen or 5 seconds elapses the splash screen will be replaced with the HomePageWidget. bloc code controls the starting and stopping of the timer using an timerState event.
'package:flutter/material.dart';
import 'bloc_splash.dart';
import 'main.dart';
class SplashWidget extends StatelessWidget {
const SplashWidget({Key? key}) : super(key: key);
_redirectToHome(BuildContext context)
{
Navigator.pushReplacement(context,MaterialPageRoute(builder:(_)=>MyHomePage(title:"helloWorld")));
}
String _displayClock(Time ? data)
{
String retVal="";
if (data!=null)
{
retVal="Time: ${data.hour} : ${data.minute} : ${data.second}";
}
return retVal;
}
#override
Widget build(BuildContext context) {
SplashBloc _bloc=SplashBloc();
_bloc.timerOnChange(StartTimer());
return Scaffold(
body:InkWell(
onTap: (){_bloc.timerOnChange(StopTimer());
_redirectToHome(context);
},
child:Container(
child:
StreamBuilder<TimeState>(
stream:_bloc.timeStream,
builder:(context,snapshot)
{
if(snapshot.hasData && (snapshot.data is RedirectState))
{
return MyHomePage(title:"helloWorld");
}
return Center(child:Column(
mainAxisAlignment: MainAxisAlignment.center,
children: [
Text("Splash Screen", style:TextStyle(fontSize: 24,fontWeight: FontWeight.bold)),
Text(_displayClock(snapshot.data?.time)),
]));
}
)
))
);
}
}
bloc code
import 'package:equatable/equatable.dart';
import 'package:flutter/material.dart';
import 'package:rxdart/rxdart.dart';
import 'dart:ui';
import 'dart:async';
abstract class TimerEvent extends Equatable{
const TimerEvent();
#override
List<Object>get props=>[];
}
class StartTimer extends TimerEvent{
const StartTimer();
}
class StopTimer extends TimerEvent{
const StopTimer();
}
class Time{
final int hour;
final int minute;
final int second;
Time(this.hour,this.minute,this.second);
}
class TimeState extends Equatable{
final Time time;
TimeState(this.time);
#override
List<Object> get props=>[time];
}
class RedirectState implements TimeState{
final Time time;
RedirectState(this.time);
#override
List<Object> get props=>[time];
#override
// TODO: implement stringify
bool? get stringify => throw UnimplementedError();
}
class TimerState extends Equatable{
final bool started;
const TimerState(this.started);
#override
List<Object> get props => [started];
}
class SplashBloc
{
SplashBloc();
Timer ?_timer;
var countDown=5;
Stream<TimeState> get timeStream=> _timeController.stream;
final _timeController =BehaviorSubject<TimeState>();
void dispose()
{
_timeController.close();
}
void _pushTimeOnTheStream(Timer timer)
{
DateTime now=DateTime.now();
_timeController.sink.add(TimeState(Time(now.hour,now.minute,now.second)));
this.countDown-=1;
if (this.countDown==0)
{
timerOnChange(StopTimer());
_timeController.sink.add(RedirectState(Time(0,0,0)));
}
}
void timerOnChange(TimerEvent event) {
if (event is StartTimer)
{
_timer=Timer.periodic(Duration(seconds: 1),_pushTimeOnTheStream);
}
else if(event is StopTimer){
//_timerController.sink.add(TimerState(false));
_timer?.cancel();
}
}
}
app
class MyApp extends StatelessWidget {
const MyApp({Key? key}) : super(key: key);
// This widget is the root of your application.
#override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Flutter Demo',
theme: ThemeData(
primarySwatch: Colors.blue,
),
home: const SplashWidget(),
);
}
}