iOS Development Skill

Quick orientation

Before anything else, identify:

1. UI framework → SwiftUI / UIKit / mixed?
2. Architecture → MVVM / TCA / VIPER / Clean / MVC?
3. iOS target → iOS 16 / 17 / 18? (affects API availability)
4. Task type → new feature / debug / refactor / architecture / performance / release?
5. Graphics intensity → стандартный UI / средняя 3D / тяжёлая графика / Metal?

Если задача связана с Metal, GPU, рендерингом, шейдерами, TBDR, MetalFX, GPU profiling, frame pacing, PSO, heaps, ICB, MTLIO → читать references/metal-graphics.md первым.

Then read the relevant reference file before writing code.

Reference files — read when needed

iOS version matrix (API availability)

Always check target before using newer APIs. Use #available guards for backward compatibility:

if #available(iOS 17, *) {
    // SwiftData or @Observable
} else {
    // fallback
}

Core Swift patterns (always apply)

Concurrency — async/await first

// Prefer this
func loadUser() async throws -> User {
    let data = try await URLSession.shared.data(from: url).0
    return try JSONDecoder().decode(User.self, from: data)
}

// Call site
Task {
    do {
        user = try await loadUser()
    } catch {
        errorMessage = error.localizedDescription
    }
}

Error handling — typed errors

enum AppError: LocalizedError {
    case networkUnavailable
    case decodingFailed(String)
    case unauthorized
    
    var errorDescription: String? {
        switch self {
        case .networkUnavailable: return "No internet connection"
        case .decodingFailed(let detail): return "Data error: \(detail)"
        case .unauthorized: return "Please sign in again"
        }
    }
}

Value types first

Prefer struct over class unless you need reference semantics, inheritance, or @Observable.

Architecture decision tree

Is the screen purely data-display with simple interaction?
  YES → MVC / simple SwiftUI View with @State is fine
  NO ↓

Is business logic testable without UI?
  Required → use ViewModel (MVVM) or Store (TCA)

Is navigation/routing complex (deep links, coordinator)?
  YES → read references/navigation.md → Coordinator pattern

Is the team large or is this a long-lived product?
  YES → Clean Architecture or TCA → read references/architecture.md

Default for most apps: MVVM + Coordinator

State management quick reference

SwiftUI state hierarchy

Local transient state       → @State
Passed from parent          → @Binding
Shared across views         → @StateObject / @ObservedObject (iOS 16-)
                            → @State with @Observable class (iOS 17+)
App-wide environment        → @EnvironmentObject / @Environment

iOS 17+ preferred (@Observable)

@Observable
class UserStore {
    var users: [User] = []
    var isLoading = false
}

// In View — no property wrapper needed
struct UserListView: View {
    var store: UserStore  // just pass it
    var body: some View {
        List(store.users) { Text($0.name) }
    }
}

iOS 16 and below (ObservableObject)

class UserViewModel: ObservableObject {
    @Published var users: [User] = []
    @Published var isLoading = false
}

struct UserListView: View {
    @StateObject private var vm = UserViewModel()
}

Xcode & project setup checklist

New project:

• Set deployment target explicitly
• Enable Swift strict concurrency warnings (SWIFT_STRICT_CONCURRENCY = complete)
• Add .gitignore for Xcode (xcuserdata, DerivedData)
• Configure signing (automatic vs manual)
• Set bundle ID and version/build numbers

Capabilities to enable when needed:

• Push Notifications → add Push Notifications capability
• Background fetch → Background Modes
• iCloud/CloudKit → iCloud
• Sign in with Apple → Sign In with Apple

Testing baseline

// Unit test — ViewModel
@MainActor
final class UserViewModelTests: XCTestCase {
    func testLoadUsers() async throws {
        let vm = UserViewModel(service: MockUserService())
        await vm.loadUsers()
        XCTAssertFalse(vm.users.isEmpty)
    }
}

// UI test — basic
func testLoginFlow() {
    let app = XCUIApplication()
    app.launch()
    app.textFields["Email"].tap()
    app.textFields["Email"].typeText("test@example.com")
    app.buttons["Continue"].tap()
    XCTAssertTrue(app.navigationBars["Home"].exists)
}

Common pitfalls

Hardware budget ориентиры (GPU capability levels)

Планировать по capability-уровням, не под конкретную модель. Всегда включать adaptive quality.

Важно: даже флагманы упираются в термальную стабильность при длительной нагрузке, а не в пиковую мощность GPU.

App Store submission checklist

• Increment build number for every TestFlight upload
• Privacy manifest (PrivacyInfo.xcprivacy) required for sensitive APIs
• App icons all sizes provided (use Asset Catalog)
• Screenshots for all required device sizes
• Export compliance (encryption questions)
• App Review Information filled in
• No UIRequiresFullScreen = NO without iPad support reasoning