Demystifying the Flutter BLoC Pattern: A Comprehensive How-To Guide

Flutter is an open-source mobile application development framework created by Google that enables developers to build high-performance, visually appealing, and cross-platform mobile applications with ease. However, as the complexity of the application increases, so does the need for proper state management. That’s where Flutter BLoC (Business Logic Component) pattern comes in.

Flutter BLoC pattern is a design pattern that separates the business logic from the UI layer of the application. It helps to manage the state of the application in a more predictable, scalable, and testable way.

In this blog, we will take a closer look at what the Flutter BLoC pattern is, how it works, and how to implement it in your Flutter application.

Related read: State Management Using Flutter BloC

What is Flutter BLoC Pattern?

The Flutter BLoC pattern is a state management pattern that follows the principles of reactive programming. It separates the business logic of an application from its user interface, making it easier to manage and test.

In simple terms, the BLoC pattern is a middle layer between the UI and the data sources of the application. It receives input from the user and processes it, then updates the UI based on the output.

The BLoC pattern consists of three main components:

  1. The Business Logic Component (BLoC): This is the core component of the pattern that holds the business logic and state of the application. It receives input events from the UI layer and processes them, then emits output events to update the UI layer.
  2. The User Interface (UI) Layer: This is the presentation layer of the application that interacts with the user. It sends input events to the BLoC layer and receives output events from it to update the UI.
  3. The Data Source Layer: This is the layer that provides data to the BLoC layer. It could be a network request, a local database, or any other data source.

How Does Flutter BLoC Pattern Work?

The Flutter BLoC pattern works by following a simple flow of events. When a user interacts with the UI layer, it sends an input event to the BLoC layer. The BLoC layer processes the input event and updates its state accordingly. It then emits an output event that the UI layer can use to update itself.

The BLoC layer can also interact with the data source layer to retrieve or update data. This data is then processed by the BLoC layer before emitting an output event. This process ensures that the UI layer always receives the latest and most accurate data.

Implementing Flutter BLoC Pattern

To implement the Flutter BLoC pattern in your application, you’ll need to follow these steps:

Step 1 – Create the BLoC class: This class will hold the business logic and state of your application. It should extend the “Bloc” class from the “bloc” package.

Step 2 – Define the input and output events: These events will be used to communicate between the UI and BLoC layers.

Step 3 – Implement the “mapEventToState” method: This method will receive the input events and update the state of the BLoC accordingly.

Step 4 – Use the “StreamBuilder” widget: This widget will listen to the output events from the BLoC layer and update the UI accordingly.

Step 5 – Inject the BLoC: Finally, you’ll need to inject the BLoC instance into your UI layer using the “BlocProvider” widget from the “bloc” package.

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Benefits of BLoC Pattern

One of the main benefits of using the BLoC pattern in your Flutter app is that it makes it easier to test your code. Because the business logic layer is separate from the presentation layer, you can test it in isolation using unit tests. This allows you to quickly catch and fix bugs before they cause issues in the rest of your app.

In addition to testing, the BLoC pattern also makes it easier to maintain and scale your app. Because the business logic is separate from the presentation layer, you can easily add new features or change the UI without affecting the underlying logic. This makes it easier to iterate on your app and adapt to changing user needs.



Flutter BLoC pattern is a powerful state management pattern that can help you build more scalable and maintainable Flutter applications. It separates the business logic from the presentation layer, making it easier to test, maintain, and scale your app.

If you are new to Flutter or looking for a better way to structure your app, consider using the BLoC pattern and the bloc library. With its set of tools and community support, the BLoC pattern is a great choice for building Flutter apps.

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