Exploring Layered Architecture: ExpenseTracker

A project to learn the ropes of using the repository design pattern in a thin domain-based architecture for iOS applications inspired by Clean Architecture. It improves separation of concerns and testability, and since all layers are separate, tests for all parts are able to be written separately and concisely.

Implementation

Clean MVVM + Repository pattern with protocol-based data access
Domain layer for holding models and repository protocols
Swift 6 Complete Concurrency Checking
Single source of truth for shared data (actor-based storage)
Support for multiple data sources (InMemory, SwiftData)
ViewModels expose async methods instead of handling Tasks
Swift Testing suite with full coverage of Services, ViewModels and Repositories
Simple dependency injection using a ViewModelFactory

Architecture

This architecture separates responsibilities across four layers. The UI layer stays free of business logic and simply displays state and sends back actions. The Application layer handles most behaviors, it reacts to user input through ViewModels and bridges them with dependencies through Services. The Data layer implements access to databases and APIs, and the conversion between external formats and internal models. Dictating all of it is the Domain layer, which defines the heart of the app. It acts as a stable bridge between the Application and Data layers by exposing the core models to be used and the interfaces for data access (like repositories). In this example project, business rules are applied in the Services and not the Domain layer like in other common cases.

+---------------+-----------------+
|      UI       | - Views         |
+---------------+-----------------+
                v
+---------------+-----------------+
|               | - Models        |
|  Application  | - Services      |
|               | - ViewModels    |
+---------------+-----------------+
                v
+---------------+-----------------+
|               | - Models        |
|    Domain     | - Repositories  |
|               |                 |
+---------------+-----------------+
                ^
+---------------+----------------------+
|               | - Repositories       |
|     Data      | - DataSources + DTO  |
|               | - Storages           |
+---------------+----------------------+

viniciusbinder/LayeredArchitectureExample

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