Native IOS

Native iOS (Swift / SwiftUI) Skill

When to use

• Creating or modifying SwiftUI views, view models, or UIKit view controllers
• Designing data flow with @State, @StateObject, @EnvironmentObject, or the Observation framework
• Integrating system frameworks (Core Location, HealthKit, StoreKit 2, ARKit, etc.)
• Configuring Xcode project settings, signing, capabilities, or schemes
• Diagnosing hangs, memory leaks, or excessive CPU in Instruments
• Preparing an app for App Store review and submission

Workflow

1. Confirm minimum deployment target and Swift version — check IPHONEOS_DEPLOYMENT_TARGET and SWIFT_VERSION in the .xcconfig or project settings. New APIs must be guarded with @available(iOS X, *).
2. Architecture decision (align with team before coding):
   • SwiftUI + Observable / MVVM: @Observable view models (iOS 17+) or ObservableObject + @StateObject (iOS 14+); one @Observable class per screen
   • TCA (The Composable Architecture): use for complex multi-screen state with explicit side-effect control
   • UIKit + Coordinators: only for brownfield additions or when SwiftUI's capabilities are insufficient for the target OS
3. SwiftUI view structure:
   • Keep View bodies thin — extract sub-views into separate View structs when a body exceeds ~30 lines
   • Pass only the data a subview needs; avoid threading @EnvironmentObject through more than two levels
   • Use @ViewBuilder for conditional branching inside reusable components
4. Swift concurrency:
   • Mark all UI updates on @MainActor; annotate view models with @MainActor at the class level
   • Use async/await for network and disk I/O; use Task { } to bridge to the async world from synchronous contexts
   • Cancel tasks in onDisappear or deinit via task.cancel() or SwiftUI's .task modifier (auto-cancelled on disappear)
5. Data persistence:
   • Simple key-value: UserDefaults (non-sensitive) or Keychain (sensitive tokens/passwords via Security framework or KeychainAccess package)
   • Relational: SwiftData (iOS 17+) or Core Data with NSPersistentCloudKitContainer for CloudKit sync
   • Network cache: URLCache with appropriate cache policies; NSCache for in-memory object caching
6. Networking:
   • Use URLSession with async/await; wrap in a typed APIClient struct
   • Validate SSL pinning for high-security apps via URLSessionDelegate
   • Never store raw API responses; decode into typed Codable models immediately
7. Instruments pass before release:
   • Leaks instrument: look for retain cycles (common with closures capturing self strongly)
   • Time Profiler: identify hangs >250 ms on the main thread
   • Memory Graph Debugger in Xcode: catch strong reference cycles in SwiftUI view model graphs
8. App Store preparation:
   • Privacy manifest (PrivacyInfo.xcprivacy) required for all apps; list all API categories used
   • App Tracking Transparency: request with ATTrackingManager.requestTrackingAuthorization before any ad SDK init
   • Review Info.plist usage description strings for every permission; Apple rejects vague strings
   • Archive with Product → Archive; validate and distribute via Xcode Organizer or altool / notarytool

Standards

Common mistakes to avoid

• Retain cycles in @escaping closures — closures stored as properties (timer callbacks, notification observers, Combine sinks) commonly capture self strongly. Use [weak self] and guard-unwrap.
• Modifying @State or publishing from a background thread — SwiftUI state must be mutated on the main actor. Use await MainActor.run { } or @MainActor annotation.
• @StateObject vs @ObservedObject confusion — @StateObject creates and owns the object (use in the view that initialises it); @ObservedObject observes an externally-provided object.
• Missing @available guards — using iOS 17 APIs without @available(iOS 17, *) causes crashes on older devices at runtime, not compile time, unless IPHONEOS_DEPLOYMENT_TARGET is set correctly.
• Storing large data in UserDefaults — UserDefaults is loaded entirely into memory on app launch; store only lightweight preferences, never images or binary blobs.
• Not unregistering NotificationCenter observers (pre-iOS 11 pattern) — in modern Swift, addObserver(forName:) returns a token that must be retained and passed to removeObserver or the block fires after dealloc.
• Skipping the privacy manifest — App Store Connect rejects submissions that use required reason APIs (file timestamps, user defaults, etc.) without a corresponding entry in PrivacyInfo.xcprivacy.

Output format

Typical feature deliverable structure:

Sources/
  Features/
    <Feature>/
      <Feature>View.swift          # SwiftUI view; thin, delegates to VM
      <Feature>ViewModel.swift     # @Observable or ObservableObject; @MainActor
      <Feature>Model.swift         # Codable data model
  Core/
    Networking/
      APIClient.swift              # URLSession wrapper; typed request/response
    Persistence/
      PersistenceController.swift  # SwiftData/Core Data stack
    Keychain/
      KeychainService.swift        # Typed Keychain read/write
Tests/
  <Feature>ViewModelTests.swift
  <Feature>APIClientTests.swift

Related checklists

• .claude/checklists/security.md
• .claude/checklists/performance.md
• .claude/checklists/accessibility.md
• .claude/checklists/production.md

Related agents

• .claude/agents/engineering/mobile-engineer.md
• .claude/agents/design/mobile-ux-specialist.md
• .claude/agents/quality/performance-engineer.md
• .claude/agents/quality/security-auditor.md
• .claude/agents/quality/accessibility-auditor.md