What is Bloc?

Learn how Bloc manages an event -> state flow.

What is Bloc?

Bloc (Business Logic Component) is a state management library that transforms incoming events into new states. Events are sent to the Bloc, the Bloc processes them and emits the resulting state. This unidirectional flow makes state changes predictable.

event -> Bloc -> state

Bloc separates business logic from the UI.

Event and State flow

A Bloc listens to events with on<Event> and produces new state with emit. The state is published as a Stream; listening widgets update on every new state.

on<Increment>((event, emit) {
  emit(CounterState(state.value + 1));
});

This flow is testable and observable.

Exercise Define the SayacBloc class

Make SayacBloc extend Bloc<SayacEvent, SayacState>. Listen to the event with on<Artir> and produce a new state with emit. In main, call print('bloc hazır').

Show example solution

import 'package:flutter_bloc/flutter_bloc.dart';

abstract class SayacEvent {}
class Artir extends SayacEvent {}

class SayacState {
  final int deger;
  SayacState(this.deger);
}

class SayacBloc extends Bloc<SayacEvent, SayacState> {
  SayacBloc() : super(SayacState(0)) {
    on<Artir>((event, emit) {
      emit(SayacState(state.deger + 1));
    });
  }
}

void main() {
  print('bloc hazır');
}

Test yourself

What does Bloc transform?
- Widgets into states
- States into widgets
- Events into states
- States into events
Show answer

Events into states — Bloc processes incoming events and produces corresponding states. This unidirectional flow goes event -> state.

Complete the Bloc class signature

class SayacBloc extends Bloc<SayacEvent, ____> {
  // ...
}

Show answer

class SayacBloc extends Bloc<SayacEvent, SayacState> {
  // ...
}

Bloc parts

Bloc

Transforms events into states
Event

Change request sent to Bloc
State

State produced by Bloc
emit

Method to publish new state

Next lesson: Cubit

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