Clean Architecture in Flutter: A Practical Guide

The Problem

As Flutter applications grow, codebases become harder to maintain. Without clear structure, you end up with:

• Business logic mixed with UI code
• Difficult-to-test components
• Features that break when you touch unrelated code

The Insight

Clean Architecture separates concerns into layers with clear boundaries:

1. Presentation Layer — UI components, state management (BLoC)
2. Domain Layer — Business logic, use cases, entities
3. Data Layer — Repositories, data sources, APIs

Each layer only depends on layers below it. The domain layer has zero dependencies on Flutter or external packages.

Practical Takeaway

Start simple. You don’t need every layer from day one:

// Start with a basic structure
lib/
  features/
    auth/
      presentation/   # Screens, widgets, BLoC
      domain/         # Entities, use cases
      data/           # Repository, API calls

Add complexity only when you need it. The goal isn’t perfection—it’s maintainability.

Key rule: If you can’t write a unit test for your business logic without mocking Flutter widgets, your architecture needs work.