Flutter Bloc Theory: A Deep Dive into Bloc State Management

4 min readOct 19, 2023

Unlock the power of Flutter Bloc State Management as we explore its theoretical foundations in this comprehensive guide. Learn how Bloc separates UI from logic, and gain insights into when, why, and how to use Bloc in your Flutter projects. Stay tuned for upcoming coding tutorials and projects!

Welcome to a fascinating journey into Flutter Bloc theory, where we unravel the complexities and nuances of this state management solution. In this blog post, we will dive deep into the theoretical aspects of Flutter Bloc, shedding light on why it’s essential and how it revolutionizes app development.

📖Read more about Flutter — visit here

Unveiling the Power of Flutter Bloc Theory

What is Bloc?

Bloc is a state management library for Flutter that is based on the BLoC pattern. The BLoC pattern separates the UI from the business logic, making the code more modular, testable, and maintainable.

Here is a more detailed explanation of the key concepts in Flutter Bloc:

Events: Events are user actions or other changes that can affect the state of the app. For example, a button click or a network request could be considered an event.
States: States are the different configurations of data that the app can be in. For example, a login app might have a state of loggedIn or loggedOut.
Blocs: Blocs are objects that manage state and business logic. They listen for events and emit new states in response.
Streams: Streams are a way to represent asynchronous data. Blocs use streams to emit new states and to receive events.

To use Flutter Bloc, you first need to create a Bloc class for each state that you need to manage in your app. The Bloc class will contain the business logic for updating the state.

Once you have created a Bloc class, you need to wrap your UI in a BlocBuilder widget. The BlocBuilder widget will listen for changes to the state and update the UI accordingly.

Finally, you need to dispatch events to the Bloc class whenever the user interacts with your app. The Bloc class will then update the state in response to the event.

Here is a simple example of how to use Flutter Bloc:

class CounterBloc {
  final Stream<int> _counterStream;

  CounterBloc() {
    _counterStream = StreamController<int>().stream;
  }

  void increment() {
    _counterStream.add(_counterStream.value! + 1);
  }

  Stream<int> get counter => _counterStream;
}

class CounterWidget extends StatelessWidget {
  final CounterBloc _counterBloc;

  const CounterWidget({
    Key? key,
    required CounterBloc counterBloc,
  }) : _counterBloc = counterBloc, super(key: key);

  @override
  Widget build(BuildContext context) {
    return BlocBuilder<CounterBloc, int>(
      bloc: _counterBloc,
      builder: (context, count) {
        return Text('Counter: $count');
      },
    );
  }
}

In this example, we have a CounterBloc class that manages the state of a counter. The CounterBloc class has a counter stream that emits the current value of the counter.

We also have a CounterWidget class that displays the current value of the counter. The CounterWidget class uses a BlocBuilder widget to listen for changes to the CounterBloc state.

When the user taps the counter, the CounterWidget dispatches an increment() event to the CounterBloc. The CounterBloc then increments the counter and emits a new state. The BlocBuilder widget then updates the UI to display the new counter value.

This is just a simple example of how to use Flutter Bloc. Bloc can be used to manage state in complex applications with multiple screens and dynamic user interfaces.

Benefits of using Flutter Bloc

There are many benefits to using Flutter Bloc, including:

Separation of UI and logic: Bloc decouples the UI from the business logic, making the code more modular and reusable. This also makes it easier to test the business logic in isolation.
Reactive programming: Bloc uses streams to implement a reactive programming model. This means that the UI is updated automatically whenever the state changes. This makes it easy to create complex and dynamic user interfaces.
Testability: Bloc is designed to be easily testable. The business logic can be tested in isolation using unit tests, and the UI can be tested using integration tests.
Performance: Bloc is highly performant, even for complex applications. This is because it uses a lightweight and efficient implementation of streams.

When to use Flutter Bloc

Flutter Bloc is a good choice for any Flutter application that needs to manage state. However, it is particularly well-suited for complex applications with multiple screens and dynamic user interfaces.

Here are some specific examples of when you might want to use Flutter Bloc:

When you have a complex UI with multiple screens and dynamic data.
When you need to share the state between different parts of your app.
When you need to make your code more modular, testable, and maintainable.

Practical Implementation: Bloc Listener, Bloc Builder, and Bloc Consumer

Bloc Listener

A Bloc Listener is used when you need to respond to state changes by calling functions, such as displaying snack bars or performing specific actions in response to a state change. It’s a valuable tool for updating the UI based on state transitions.

Bloc Builder

When you want to build specific widgets based on state changes, Bloc Builder comes into play. It helps create widgets, screens, or components that respond to changes in the app’s state. For instance, if the app is in a loading state, you can display a loading spinner, while a success state would lead to the display of the app’s main content.

Bloc Consumer

Bloc Consumer combines the functionalities of both Bloc Listener and Bloc Builder. It allows you to respond to state changes by executing functions and building widgets simultaneously. This is particularly useful for situations where you need to both update the UI and call functions in response to state changes.