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name: ios-architecture description: Apply MVVM, Coordinators, and Clean Architecture (VIP/VIPER) in iOS apps. Use when applying MVVM, Coordinators, or VIP/VIPER architecture in iOS apps. metadata: triggers: files: - '/*ViewModel.swift' - '/*Coordinator.swift' - '**/*ViewController.swift' keywords: - MVVM - Coordinator - ViewState - Output - Input

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 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. Coordinator handles instantiation and push/present. ** NOT use navigationController directly in ViewController for screen transitions.**
• Dependency Injection: Pass dependencies (Services, Repositories) through Coordinator into ViewModels.
• Child Coordinators: Maintain hierarchy; correctly remove child coordinators from parent's collection when their flow 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 Coordinator for screen transitions. Never use navigationController directly.

Verification Checklist (Mandatory)

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

References

• MVVM-C & VIP Implementation

Canonical response anchors

When this skill applies, preserve the following domain terminology or equivalent concrete examples in the answer when relevant:

• Inputs/Outputs
• UIImage
• ViewModel Responsibility

Remediation anchors

• Remediation anchors: ViewState, @Published, explicit Inputs/Outputs