Clean Architecture layers in Flutter - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the main purpose of the Presentation Layer in Clean Architecture?

The Presentation Layer handles the user interface and user interactions. It shows data to the user and sends user actions to the next layer.

beginner

Define the role of the Domain Layer in Clean Architecture.

The Domain Layer contains the business rules and logic. It is independent of UI or data sources and focuses on what the app does.

beginner

What does the Data Layer do in Clean Architecture?

The Data Layer manages data sources like databases, APIs, or local storage. It fetches and saves data and converts it to a form the Domain Layer understands.

intermediate

Why is it important that the Domain Layer is independent of other layers?

Independence means business rules don’t depend on UI or data details. This makes the app easier to test, maintain, and change without breaking core logic.

intermediate

How do the layers in Clean Architecture communicate with each other?

Layers communicate through interfaces or abstractions. The Presentation Layer calls the Domain Layer, which calls the Data Layer. This keeps layers separate and flexible.

Which layer in Clean Architecture is responsible for business rules?

A Data Layer

B Presentation Layer

C Domain Layer

D UI Layer

The Domain Layer contains the business rules and logic.

What does the Data Layer mainly handle?

A Business logic

B Data sources like APIs and databases

C User interface

D Navigation

The Data Layer manages data sources such as APIs and databases.

Why should the Domain Layer be independent?

A To allow easy testing and maintenance

B To handle user input

C To speed up data fetching

D To make UI look better

Independence allows easy testing and maintenance of business rules.

Which layer directly interacts with the user?

A Presentation Layer

B Domain Layer

C Data Layer

D Repository Layer

The Presentation Layer handles user interface and interactions.

How do layers communicate in Clean Architecture?

A Directly accessing each other's data

B By sharing UI components

C Using global variables

D Through interfaces or abstractions

Layers communicate through interfaces or abstractions to keep separation.

Explain the three main layers of Clean Architecture and their responsibilities.

Think about what each layer does in a simple app.

Why is it beneficial to keep the Domain Layer independent from the Presentation and Data Layers?

Consider how changes in UI or data sources should not break core logic.

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