Clean Architecture layers in Flutter

Introduction

Clean Architecture helps organize your app into clear parts. This makes your app easier to build, test, and change later.

When building an app that will grow bigger over time.

When you want to keep your app easy to fix and add new features.

When working with a team to keep code clear and organized.

When you want to separate app logic from user interface.

When you want to write tests for your app easily.

Syntax

Flutter

Presentation Layer
Domain Layer
Data Layer

Presentation Layer: Shows UI and handles user actions.

Domain Layer: Contains app rules and logic, independent of UI or data.

Data Layer: Manages data sources like APIs or databases.

Examples

This shows what each layer usually contains in a Flutter app.

Flutter

Presentation Layer: Flutter widgets, UI code
Domain Layer: Use cases, business rules
Data Layer: API calls, database access

Shows the flow of calls between layers.

Flutter

Presentation Layer -> calls -> Domain Layer -> calls -> Data Layer

Sample App

This Flutter app shows a simple example of Clean Architecture layers. The domain layer has a use case that returns a greeting. The presentation layer shows this greeting in the UI.

Flutter

import 'package:flutter/material.dart';

// Domain Layer: simple use case
class GetGreeting {
  String call() => 'Hello from Domain Layer!';
}

// Presentation Layer: UI widget
class MyApp extends StatelessWidget {
  final GetGreeting getGreeting = GetGreeting();

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(title: Text('Clean Architecture Example')),
        body: Center(
          child: Text(getGreeting()),
        ),
      ),
    );
  }
}

void main() => runApp(MyApp());

Important Notes

Keep domain layer free from Flutter or platform code to make it reusable.

Presentation layer depends on domain layer, but domain layer does not depend on presentation.

Data layer handles where data comes from, like web or local storage.

Summary

Clean Architecture divides app into Presentation, Domain, and Data layers.

This separation makes apps easier to maintain and test.

Presentation handles UI, Domain handles logic, Data handles data sources.

Practice

1. Which layer in Clean Architecture is responsible for handling the user interface in a Flutter app?

easy

A. Domain layer

B. Presentation layer

C. Data layer

D. Network layer

Solution

1. Step 1: Understand the role of each layer

   The Presentation layer manages UI elements and user interactions.

2. Step 2: Match the layer to UI responsibility

   Since UI is about what the user sees and interacts with, it belongs to the Presentation layer.

3. Final Answer:

   Presentation layer -> Option B

4. Quick Check:

   UI = Presentation layer [OK]

Hint: UI always belongs to Presentation layer [OK]

Common Mistakes:

• Confusing Domain layer with UI
• Thinking Data layer handles UI
• Assuming Network layer is part of UI

2. Which of the following is the correct way to describe the Domain layer in Clean Architecture?

easy

A. It contains business logic and rules.

B. It handles data storage and retrieval.

C. It manages UI components and widgets.

D. It deals with network requests and APIs.

Solution

1. Step 1: Identify the Domain layer's responsibility

   The Domain layer contains the core business logic and rules of the app.

2. Step 2: Eliminate incorrect options

   Data storage is Data layer, UI is Presentation, network is part of Data or external services.

3. Final Answer:

   It contains business logic and rules. -> Option A

4. Quick Check:

   Domain = Business logic [OK]

Hint: Domain layer = business rules and logic [OK]

Common Mistakes:

• Mixing Domain with Data layer
• Thinking Domain manages UI
• Confusing network tasks with Domain

3. Given the following Flutter app structure, which layer should contain the repository interface?

lib/
  presentation/
  domain/
    repositories/
  data/
    repositories_impl/

medium

A. Presentation layer

B. Data layer

C. Domain layer

D. UI layer

Solution

1. Step 1: Understand repository interface placement

   Repository interfaces define contracts for data access and belong in the Domain layer.

2. Step 2: Check the folder structure

   Domain layer has 'repositories' folder for interfaces; Data layer has 'repositories_impl' for implementations.

3. Final Answer:

   Domain layer -> Option C

4. Quick Check:

   Repository interface = Domain layer [OK]

Hint: Interfaces go in Domain, implementations in Data [OK]

Common Mistakes:

• Putting interfaces in Data layer
• Confusing UI layer with Presentation
• Ignoring folder naming conventions

4. In a Flutter app using Clean Architecture, a developer places API call code directly inside a widget class. What is the main problem with this approach?

medium

A. It violates the separation of concerns by mixing UI and data logic.

B. It improves app performance by reducing layers.

C. It follows Clean Architecture best practices.

D. It makes the Domain layer responsible for UI.

Solution

1. Step 1: Identify the problem with API calls in UI

   API calls belong in the Data layer, not in UI widgets.

2. Step 2: Understand separation of concerns

   Mixing UI and data logic breaks Clean Architecture principles, making code harder to maintain.

3. Final Answer:

   It violates the separation of concerns by mixing UI and data logic. -> Option A

4. Quick Check:

   UI should not contain data logic [OK]

Hint: Keep API calls out of UI widgets [OK]

Common Mistakes:

• Thinking mixing layers improves performance
• Assuming Domain layer handles UI
• Believing this is best practice

5. You want to add a new feature to your Flutter app that fetches user profiles from a remote server. According to Clean Architecture, where should you place the code that converts JSON data into Dart objects?

hard

A. In the Presentation layer inside widgets

B. In the Domain layer as part of business logic

C. Directly inside the main.dart file

D. In the Data layer within model or mapper classes

Solution

1. Step 1: Identify JSON conversion responsibility

   Converting JSON to Dart objects is a data transformation task, part of data handling.

2. Step 2: Match task to Clean Architecture layer

   Data layer handles data sources and transformations, so JSON parsing belongs here.

3. Step 3: Exclude other layers

   Presentation is UI only, Domain is business rules, main.dart is app entry point, not for data parsing.

4. Final Answer:

   In the Data layer within model or mapper classes -> Option D

5. Quick Check:

   JSON parsing = Data layer [OK]

Hint: Put JSON parsing in Data layer models/mappers [OK]

Common Mistakes:

• Parsing JSON in UI widgets
• Putting parsing in Domain layer logic
• Adding parsing code in main.dart