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What is BLoC?

BLoC (Business Logic Component) is a state management pattern that helps separate business logic from the UI layer in Flutter applications. It was developed by Google and is now one of the most popular state management solutions in the Flutter ecosystem.

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Why BLoC?

  1. Separation of Concerns

    • Clear separation between UI and business logic
    • Makes code more maintainable and testable
    • Follows the Single Responsibility Principle

  2. Predictable State Changes

    • Unidirectional data flow
    • States are immutable
    • Easy to track state changes and debug

  3. Scalability

    • Perfect for complex applications
    • Handles asynchronous data streams efficiently
    • Great for large teams and enterprise applications

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Core Concepts

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Events

Events are the input to a BLoC. They are dispatched in response to user interactions or other triggers like API responses or timer completions.

abstract class CounterEvent {}

class IncrementPressed extends CounterEvent {}
class DecrementPressed extends CounterEvent {}

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States

States represent the output of a BLoC and are the result of processed events.

abstract class CounterState {
  final int count;
  const CounterState(this.count);
}

class CounterInitial extends CounterState {
  const CounterInitial() : super(0);
}

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BLoC

The BLoC itself contains the business logic that transforms events into states.

class CounterBloc extends Bloc<CounterEvent, CounterState> {
  CounterBloc() : super(const CounterInitial()) {
    on<IncrementPressed>((event, emit) {
      emit(CounterState(state.count + 1));
    });
  }
}

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When to Use BLoC?

BLoC is particularly useful when:

  • Your app has complex business logic
  • You need to manage multiple states across different screens
  • You’re working with real-time data or streams
  • You need to implement complex user interactions
  • You want to make your code more testable

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Best Practices

  1. Keep BLoCs focused and single-purpose
  2. Use meaningful names for events and states
  3. Handle errors appropriately
  4. Test your BLoCs thoroughly
  5. Don’t put UI logic in BLoCs

In the next sections, we’ll explore how to implement BLoC with Freezed for better immutability and code generation, and dive deeper into best practices for real-world applications.