isolate_bloc

Description:

isolate bloc

Overview #
The goal of this package is to make it easy to work with BLoC and Isolate.
The main difference from another BLoC pattern implementations is what blocs
work in Isolate
and don't slow down UI.
This package works on all flutter platforms.
You can read about BLoC pattern here.
Index #

Attention
Bloc and Cubit
Creating

IsolateCubit
IsolateBloc


Registering a Bloc or Cubit
Using Bloc or Cubit in UI
All Api

IsolateBlocWrapper
Initialization
Create new Bloc instance
Consume Bloc
Blocs Observer
Use Bloc in another Bloc
Use platform channels


Examples

Attention #
I recommend you to read about Isolates to get to know their weaknesses and strengths.

Performance of isolates (before Flutter 2.8)
Lightweight isolates (since Flutter 2.8)
New kinds of objects that can be sent between isolates (since Flutter 2.8)

In brief, isolates share memory, so immutable objects are not copied when transferred to another isolate.
You can now use them without being afraid but you shouldn't forget that there are still
some limitations and overhead costs.
Bloc and Cubit #



In Bloc, events are processed strictly in turn. It gets an event and responds to it with a stream of states in mapEventToState. Until the stream ends, the processing of a new event will not begin.
In Cubit, events are received in onEventReceived and processed asynchronously, and the state is returned by the emit function.
Creating #
IsolateCubit #
/// Cubit for counter with `CounterEvent` and `int` state.
class CounterCubit extends IsolateCubit<CountEvent, int> {
/// The initial state of the `CounterCubit` is 0.
CounterCubit() : super(0);

/// When `CountEvent` is received, the current state
/// of the bloc is accessed via `state` and
/// a new `state` is emitted via `emit`.
@override
void onEventReceived(CountEvent event) {
emit(event == CountEvent.increment ? state+1 : state-1);
}
}
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IsolateBloc #
class CounterBloc extends IsolateBloc<CountEvent, int> {
/// The initial state of the `CounterBloc` is 0.
CounterBloc() : super(0);

/// When `CountEvent` is received, the current state
/// of the bloc is accessed via `state` and
/// and a new state is emitted via `yield`.
Stream<int> mapEventToState(CountEvent event) async* {
yield event == CountEvent.increment ? state+1 : state-1;
}
}
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Registering a Bloc or Cubit #
To be able to create Bloc you need to register it. You can do with the register function.
void main() async {
await initialize(isolatedFunc);
...
}

/// Global function which is used to register blocs or cubits and called in Isolate
void isolatedFunc() {
/// Register a bloc or cubit to be able to create it in main Isolate
register<CounterBloc, int>(create: () => CounterBloc());
}
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register function will create one instance of all registered blocs to get their initial states.
To prevent this you may provide initial state to the register function.
register<CounterBloc, int>(
create: () => CounterBloc(),
initialState: 0,
)
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Using Bloc or Cubit in UI #
YourWidget(
/// Create CounterBloc and provide it down to the widget tree
child: IsolateBlocProvider<CounterBloc, int>(
child: CounterScreen(),
),
)
...
class CounterScreen extends StatelessWidget {
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text('Counter'),
),
body: Center(
/// Listen for CounterBloc State
child: IsolateBlocListener<CounterBloc, int>(
listener: (context, state) => print("New bloc state: $state"),
/// Build widget based on CounterBloc's State
child: IsolateBlocBuilder<CounterBloc, int>(
builder: (context, state) {
return Text('You tapped $state times');
},
),
),
),
floatingActionButton: Column(
mainAxisSize: MainAxisSize.min,
children: [
FloatingActionButton(
heroTag: 'Increment',
/// Get bloc using extension and add new event
onPressed: () => context.isolateBloc<CounterBloc, int>().add(CountEvent.increment),
child: Icon(Icons.add),
),
SizedBox(height: 10),
FloatingActionButton(
heroTag: 'Decrement',
/// Get bloc using provider class and add new event
onPressed: () => IsolateBlocProvider.of<CounterBloc, int>(context).add(CountEvent.decrement),
child: Icon(Icons.remove),
),
],
),
);
}
}
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All Api #
IsolateBlocWrapper #
IsolateBlocWrapper works like a client for IsolateBloc. It receives IsolateBloc's
states and sends events added by wrapperInstance.add(YourEvent()). So you can
listen for origin bloc's state with wrapperInstance.listen((state) { }) and add
events as shown above. createBloc<BlocA, BlocAState>() function creates IsolateBloc in
Isolate and returns IsolateBlocWrapper.
// Create counter bloc and receive it's wrapper
IsolateBlocWrapper wrapper = createBloc<CounterBloc, int>();

// Wrapper's initial state is the same as CounterBloc's initial state
assert(wrapper.state == 0);

// This event will be sent to the CounterBloc
wrapper.add(CounterEvent.increment);

wrapper.listen((state) => print('CounterBloc state: $state'));
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Initialization #
To create Isolate and register Blocs you need to call initialize and provide initialization (isolated) function. This function will be executed in Isolate and it MUST be a GLOBAL or STATIC.
void main() async {
/// Initialize
await initialize(isolatedFunc);
...
}

/// Global function is used to register blocs and called in Isolate
void isolatedFunc() {
/// Register a bloc to be able to create it in main Isolate
register(create: () => CounterBloc());
}
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Create new Bloc instance #
To create a new instance of bloc you can use Widget or function.
/// Create with Widget
IsolateBlocProvider<BlocA, BlocAState>(
child: ChildA(),
)

/// Create multiple blocs with Widget
MultiIsolateBlocProvider(
providers: [
IsolateBlocProvider<BlocA, BlocAState>(),
IsolateBlocProvider<BlocB, BlocBState>(),
IsolateBlocProvider<BlocC, BlocCState>(),
],
child: ChildA(),
)

/// Create with function
final blocA = createBloc<BlocA, BlocAState>();
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Consume Bloc #
IsolateBlocBuilder<CounterBloc, int>(
buildWhen: (state, newState) {
/// return true/false to determine whether or not
/// to rebuild the widget with state
builder: (context, state) {
/// return widget here based on CounterBloc's state
},
)

IsolateBlocListener<CounterBloc, int>(
listenWhen: (state, newState) {
/// return true/false to determine whether or not
/// to listen for state
},
listener: (context, state) {
/// listen for state
},
child: ChildWidget(),
)

IsolateBlocConsumer<CounterHistoryBloc, List<int>>(
listenWhen: (state, newState) {
/// return true/false to determine whether or not
/// to listen for state
},
listener: (context, state) {
/// listen for state
},
buildWhen: (state, newState) {
/// return true/false to determine whether or not
/// to rebuild the widget with state
},
builder: (context, state) {
/// return widget here based on BlocA's state
},
)
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Blocs Observer #
To observe single bloc or cubit you can override onError, onEvent, onChange and onTransition methods.
class CounterBloc extends IsolateBloc<CountEvent, int> {
CounterBloc() : super(0);

@override
Stream<int> mapEventToState(CounterEvent event) {...}

@override
void onError(Object error, StackTrace stackTrace) {...}

@override
void onEvent(CounterEvent event) {...}

@override
void onTransition(Transition<CounterEvent, int> transition) {...}

}
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Or you can use IsolateBlocObserver to observe all blocs or cubits.
void isolatedFunc() {
IsolateBloc.observer = SimpleBlocObserver();
register(create: () => CounterBloc());
}

class SimpleBlocObserver extends IsolateBlocObserver {
void onCreate(IsolateBlocBase bloc) {
super.onCreate(bloc);
print('New instance of ${bloc.runtimeType} created');
}

void onEvent(IsolateBlocBase bloc, Object? event) {
super.onEvent(bloc, event);
print('${event.runtimeType} is added to ${bloc.runtimeType}');
}

void onChange(IsolateBlocBase bloc, Change change) {
super.onChange(bloc, change);
print('State is emitted in ${bloc.runtimeType}. New state is ${change.nextState}');
}

void onTransition(IsolateBloc bloc, Transition transition) {
super.onTransition(bloc, transition);
print("${bloc.runtimeType}'s state updated. "
'New state is ${transition.nextState}, '
'event is ${transition.event}');
}

void onError(IsolateBlocBase bloc, Object error, StackTrace stackTrace) {
super.onError(bloc, error, stackTrace);
print('Error thrown in ${bloc.runtimeType}. Error is $error');
}

void onClose(IsolateBlocBase bloc) {
super.onClose(bloc);
print('${bloc.runtimeType} is closed');
}
}
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Use Bloc in another Bloc #
You can use Bloc in another Bloc. To do this you need to use getBloc<BlocA, BlocAState>()
function which returns IsolateBlocWrapper<BlocAState> .
This function works this way:

waits for user's [Initializer] function
looks for created bloc with BlocA type

if it finds any, so returns this bloc's [IsolateBlocWrapper]
otherwise it creates a new bloc and adds to the pull of free blocs.
So when UI will call create(), it won't create a new bloc but return free bloc from pull.



void isolatedFunc() {
register(create: () => CounterBloc());
register(create: () => CounterHistoryBloc(getBloc<CounterBloc, int>()));
}

class CounterBloc extends IsolateBloc<CountEvent, int> {
CounterBloc() : super(0);

@override
void onEventReceived(CountEvent event) {
emit(event == CountEvent.increment ? state + 1 : state - 1);
}
}

class CounterHistoryBloc extends IsolateBloc<int, List<int>> {
final IsolateBlocWrapper<int> counterBloc;
final _history = <int>[];

CounterHistoryBloc(this.counterBloc) : super([]) {
counterBloc.listen(onEventReceived);
}

@override
void onEventReceived(int event) {
emit(_history..add(event));
}
}
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Use platform channels #
You can just use platform (Method) channels in your blocs.
About some limitations you can read here.
Examples #

Counter
Weather

Articles #

Flutter. Как прокачать ваш BLoC (ru)

Helpers #

Live templates

Gratitude #
Special thanks to Felix Angelov for the reference in the form of bloc package