iOS Architecture Standards

Priority: P0 (CRITICAL)

Implementation Guidelines

MVVM (Model-View-ViewModel)

• ViewModel Responsibility: Handle business logic, formatting, and state. No UIKit imports (except for platform types like UIImage if strictly necessary).
• ViewState: Use a single state object or discrete @Published properties for UI updates. Expose state as private(set) or using publishers.
• Inputs/Outputs: Define explicit protocols or nested types for inputs (events from View) and outputs (state for View).

Coordinator Pattern

• Navigation Logic: Decouple ViewControllers from navigation logic. The Coordinator handles instantiation and push/present. Do NOT use navigationController directly in the ViewController for screen transitions.
• Dependency Injection: Pass dependencies (Services, Repositories) through the Coordinator into the ViewModels.
• Child Coordinators: Maintain a hierarchy; correctly remove child coordinators from the parent's collection when their flow is finished.

Clean Architecture (VIP/VIPER)

• VIP (Clean Swift): Use Interactor for logic, Presenter for UI formatting, and ViewController for display.
• Unidirectional Flow: Data flows: View -> Interactor -> Presenter -> View.
• VIPER: (View, Interactor, Presenter, Entity, Router) — another common architectural pattern for iOS apps.

Anti-Patterns

• No Logic in VC: Move business logic to ViewModel/Interactor.
• No Public ViewModel State: Keep state private(set) or using publishers.
• No Direct Navigation: Use a Coordinator for screen transitions. Never use navigationController directly.

Verification Checklist (Mandatory)

• Pure ViewModel: Does the ViewModel have any UIKit imports? (Prohibited)
• Navigation: Is navigationController used directly in the VC for transitions? (Use Coordinator)
• State Access: Is ViewModel state exposed as public var? (Use private(set) or publishers)
• Deallocation: Are child coordinators correctly removed from the parent's collection on finish?
• VIP Unidirection: Is the data flow unidirectional (View -> Interactor -> Presenter -> View)?

References

• MVVM-C & VIP Implementation