isolate_bloc 2.0.0 isolate_bloc: ^2.0.0 copied to clipboard
A dart package that helps implement the BLoC pattern. BLoC works in Isolate and don't slow down UI.
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.
Attention #
Before using this package, I recommend reading the article about performance of Isolate.
When moving data between isolates, they are copied, wasting memory and cpu time.
Now Dart team is working on new Isolates which can start quickly and move immutable data faster and without coping. I hope they will be able to sufficiently improve the interaction between the isolates. This will allow more people to use this package
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);
}
}
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;
}
}
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());
}
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,
)
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),
),
],
),
);
}
}
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'));
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());
}
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>();
Use a 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
},
)
Observer Blocs #
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) {...}
}
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');
}
}
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));
}
}
Use platform channels #
If you want to use platform channels (MethodChannels) or libraries which use them in your Blocs or repositories you must provide PlatformChannelSetup
with MethodChannel names in initialize
.
Below you can see example of how to add url_launcher
library support.
await initialize(
isolatedFunc,
methodChannelSetup: MethodChannelSetup(
methodChannelNames: [
'plugins.flutter.io/url_launcher',
],
),
);
By default, channels have already been added for flutter fire, flutter developers libraries
and popular community libraries. All out of box supported libraries you can see here
(look at Library.name
).
Limitations #
If you will try to send one of the following objects you will get
Illegal argument in isolate message
runtime exception.
Lambda functions #
Your event/state cannot contain anonymous functions (something like this final callback = () {}
).
Because of it you can't send BuildContext
or ThemeData
.
StackTrace #
If you will try to send exception with StackTrace you will also get runtime exception.
ReceivePort #
Just don't send this object.
Examples #
Articles #
Helpers #
Gratitude #
Special thanks to Felix Angelov for the reference in the form of bloc package