In the realm of Flutter development, efficient state management is crucial for building robust and maintainable applications. With the growing complexity of User interfaces and user interactions, developers seek reliable patterns to manage states effectively. One such pattern that has gained significant traction in the Flutter community is the Flutter Bloc pattern.
In this blog post, we’ll delve into the Flutter Bloc pattern, exploring its core concepts, benefits, and implementation with practical examples.
The Flutter Bloc pattern is a state management solution that separates the presentation layer from the business logic. It helps in organizing code and making it easier to maintain and test. In essence, it involves the following components:
Related read: State Management Using Flutter BloC
When you use Flutter bloc you are going to create events to trigger the interactions with the app and then the bloc in charge is going to emit the requested data with a state, in a real example it will be like this:
🔸 The user clicks on a button to get a list of games.
🔸 The event is triggered and it informs the bloc that the user wants a list of games.
🔸 The bloc is going to request this data ( from a repository for example, which is in charge of connecting to the API to get the data).
🔸 When the bloc has the data it will determine if the data is a Success or Error, and then it’s going to emit a state.
🔸 The view is going to be listening to all the possible states that the Flutter Bloc pattern could emit to reach them. For instance, if bloc emits Success as a state the view is going to rebuild it with a list of games, but if the state is Error the view is going to rebuild with an error message or whatever you want to show.
Let’s walk through a simple example to understand how to implement the Bloc pattern in Flutter. Suppose we have a counter application where users can increment and decrement a counter value.
Example code:
abstract class CounterEvent {}
class IncrementEvent extends CounterEvent {}
class DecrementEvent extends CounterEvent {}Example code:
import 'dart:async';
class CounterBloc {
int _counter = 0;
final _counterStateController = StreamController<int>();
StreamSink<int> get _inCounter => _counterStateController.sink;
Stream<int> get counter => _counterStateController.stream;
final _counterEventController = StreamController<CounterEvent>();
Sink<CounterEvent> get counterEventSink => _counterEventController.sink;
CounterBloc() {
_counterEventController.stream.listen(_mapEventToState);
}
void _mapEventToState(CounterEvent event) {
if (event is IncrementEvent) {
_counter++;
} else if (event is DecrementEvent) {
_counter--;
}
_inCounter.add(_counter);
}
void dispose() {
_counterStateController.close();
_counterEventController.close();
}
}Example code:
class CounterScreen extends StatelessWidget {
final CounterBloc _counterBloc = CounterBloc();
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(title: Text('Counter App')),
body: Center(
child: StreamBuilder<int>(
stream: _counterBloc.counter,
builder: (context, snapshot) {
return Text(
'${snapshot.data}',
style: TextStyle(fontSize: 24),
);
},
),
),
floatingActionButton: Column(
mainAxisAlignment: MainAxisAlignment.end,
crossAxisAlignment: CrossAxisAlignment.end,
children: <Widget>[
FloatingActionButton(
onPressed: () => _counterBloc.counterEventSink.add(IncrementEvent()),
child: Icon(Icons.add),
),
SizedBox(height: 10),
FloatingActionButton(
onPressed: () => _counterBloc.counterEventSink.add(DecrementEvent()),
child: Icon(Icons.remove),
),
],
),
);
}
}Example code:
@override
void dispose() {
_counterBloc.dispose();
super.dispose();
}
The Flutter Bloc pattern is a powerful tool for managing state in Flutter applications. By separating business logic from UI, it promotes code organization, testability, and scalability. Although it might introduce some initial overhead, especially for simple applications, its benefits become apparent as the project grows in complexity. With the example provided, you can start integrating the Bloc pattern into your Flutter projects and experience its advantages firsthand.
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