/ios-architecture

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](references/implementation.md)

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