What is Clean Architecture

Clean Architecture is a way of structuring your app so that:

• Business logic is independent
• Code is testable
• UI changes don’t break logic
• Frameworks (Flutter, Firebase, API) are replaceable

👉 In MNC terms:

“Clean Architecture separates concerns and enforces dependency rules to build scalable and maintainable apps.”

Clean Architecture Layers (Flutter)

Clean Architecture usually has 3 main layers:

Presentation → Domain → Data

1️⃣ Presentation Layer (UI)

What it contains

• Screens (Widgets)
• State management (Bloc / Provider / Riverpod)
• UI logic only

What it should NOT contain
❌ API calls
❌ Database logic
❌ Business rules

📂 Example:

presentation/
 ├── pages/
 ├── widgets/
 └── bloc/

2️⃣ Domain Layer (Heart of the App ❤️)

Most important layer

Contains

• Entities (pure models)
• Use Cases (business rules)
• Repository interfaces (abstract classes)

Depends on NOTHING

• No Flutter
• No Firebase
• No HTTP

📂 Example:

domain/
 ├── entities/
 ├── usecases/
 └── repositories/

📌 Example Use Case:

class GetUserProfile {
  final UserRepository repository;

  GetUserProfile(this.repository);

  Future<User> call() {
    return repository.getUser();
  }
}

3️⃣ Data Layer (Implementation)

Handles external data

• API
• Database
• Firebase

Contains

• Repository implementations
• Data sources (remote / local)
• DTO / Models

📂 Example:

data/
 ├── models/
 ├── datasources/
 └── repositories/

📌 Example Repository Implementation:

class UserRepositoryImpl implements UserRepository {
  final UserRemoteDataSource remoteDataSource;

  UserRepositoryImpl(this.remoteDataSource);

  @override
  Future<User> getUser() {
    return remoteDataSource.getUser();
  }
}

Dependency Rule (VERY IMPORTANT)

Dependencies always move inward 👇

UI → Domain ← Data

• Presentation depends on Domain
• Data depends on Domain
• Domain depends on NOTHING

💡 This is the #1 interview question on Clean Architecture.

How API Call Flows in Clean Architecture

Example: Fetch User Profile

UI
 ↓
Bloc / Provider
 ↓
UseCase
 ↓
Repository (interface)
 ↓
RepositoryImpl
 ↓
RemoteDataSource
 ↓
API

Why MNCs Love Clean Architecture

• 🔹 Easy testing
• 🔹 Team collaboration
• 🔹 Scalable codebase
• 🔹 Easy to add features
• 🔹 Framework independent

Clean Architecture + State Management (Flutter)

Works best with:

• ✅ Bloc
• ✅ Riverpod
• ✅ Provider

Common combo:

Flutter + Clean Architecture + Bloc

Folder Structure (MNC-ready)

lib/
 ├── core/
 │   ├── error/
 │   ├── network/
 │   └── utils/
 ├── features/
 │   └── auth/
 │       ├── presentation/
 │       ├── domain/
 │       └── data/
 └── main.dart

Clean Architecture Interview Questions (🔥 Popular)

1. Why domain layer should not depend on Flutter?
2. Difference between Entity and Model?
3. What is Use Case?
4. How dependency inversion works?
5. How do you test use cases?
6. How Clean Architecture improves scalability?

Common Mistakes ❌

• Putting API calls in Bloc
• Using Models in Domain layer
• Skipping Use Cases
• Tight coupling UI & API

One-Line Interview Answer

“Clean Architecture helps us separate UI, business logic, and data sources, making Flutter apps scalable, testable, and easy to maintain.”