Apple Development

Expert-level guidance for building native Apple applications with Swift and SwiftUI, following Apple's best practices and Human Interface Guidelines.

Core Capabilities

1. Swift Programming Excellence

Write idiomatic, performant Swift code following modern best practices:

• Type Safety & Optionals: Proper optional handling with guard, if let, nil coalescing; avoid force unwrapping
• Value Types First: Prefer struct over class; use classes for reference semantics and inheritance
• Protocol-Oriented Programming: Small focused protocols, protocol extensions with default implementations
• Modern Swift: async/await, property wrappers, Result type, Codable, Combine
• Memory Management: [weak self] in closures, avoid retain cycles, efficient resource usage
• Code Organization: Clear file structure, meaningful naming, access control, MARK comments

When to consult references: For detailed patterns, advanced techniques, or specific language features, read references/swift-best-practices.md

2. SwiftUI Interface Development

Build modern, declarative user interfaces following SwiftUI patterns:

• State Management: @State, @Binding, @StateObject, @ObservedObject, @EnvironmentObject, @Environment
• Observable Macro: Modern @Observable pattern for iOS 17+ (no @Published needed)
• MVVM Pattern: Clean separation with ViewModels, proper data flow
• View Composition: Break complex views into focused, reusable components
• Custom Modifiers: Reusable styling through ViewModifier protocol
• Navigation: NavigationStack, sheets, alerts, confirmation dialogs
• Lists & Performance: LazyVStack, ForEach optimization, equatable views
• Animations: Implicit/explicit animations, transitions, matched geometry effects

When to consult references: For layout patterns, advanced state management, or SwiftUI-specific techniques, read references/swiftui-patterns.md

3. Human Interface Guidelines Compliance

Design interfaces that feel native and follow Apple's design principles:

• Platform Conventions: iOS navigation patterns (tab bar, navigation bar), macOS window management
• Typography: SF Pro font hierarchy, Dynamic Type support, accessibility
• Color: System colors, semantic colors, dark mode support, sufficient contrast
• Layout: Safe areas, spacing system (4pt grid), standard margins, touch targets (44x44pt minimum)
• Components: Standard buttons, lists, forms, navigation, sheets, alerts
• Accessibility: VoiceOver labels, Dynamic Type, reduce motion, color contrast
• Gestures: Tap, swipe, long press, pinch, proper haptic feedback

When to consult references: For detailed HIG requirements, component specifications, or platform-specific patterns, read references/human-interface-guidelines.md

4. Apple Frameworks Mastery

Leverage the full Apple ecosystem with deep framework knowledge:

• Foundation: String, Date, FileManager, UserDefaults, Codable, URLSession
• UIKit/AppKit: View controllers, table views, collection views, Auto Layout
• SwiftUI: Declarative UI, state management, navigation, animations
• Networking: URLSession async/await, Codable JSON parsing, error handling
• Data Persistence: Core Data, SwiftData (iOS 17+), UserDefaults, file system
• Concurrency: async/await, Task, actors, MainActor, TaskGroup
• Combine: Publishers, operators, reactive programming
• CloudKit: Public/private databases, CKRecord CRUD operations
• StoreKit: In-app purchases, subscriptions, transaction handling
• Core Location & MapKit: Location services, mapping, annotations
• HealthKit: Health data queries, authorization, samples
• AVFoundation: Audio/video playback, camera capture

When to consult references: For framework APIs, code samples, or integration patterns, read references/apple-frameworks.md

5. Performance Optimization

Build fast, efficient applications with optimal resource usage:

• Launch Time: Defer initialization, lazy properties, optimize bundle size
• Memory Management: Fix leaks, reduce footprint, image optimization, caching
• CPU Optimization: Background queues, efficient algorithms, lazy operations
• Rendering: Optimize view hierarchy, SwiftUI performance, Core Animation
• Network: Reduce data transfer, batch requests, caching, offline mode
• Battery: Minimize location updates, efficient background tasks
• Database: Core Data batch operations, indexes, efficient queries
• Profiling: Instruments (Time Profiler, Allocations, Leaks), MetricKit

When to consult references: For optimization techniques, profiling workflows, or specific performance patterns, read references/performance-optimization.md

Development Workflow

Starting a New Project

1. Choose Architecture: SwiftUI-first for new apps, UIKit for legacy or specific requirements
2. Set Up Structure: MVVM for SwiftUI, MVC or VIPER for UIKit
3. Configure Project:
   • Enable Swift strict concurrency checking
   • Set deployment target appropriately
   • Configure code signing
4. Follow Conventions: File per type, MARK comments, proper access control
5. Start with HIG: Design following platform patterns before implementing

Writing Code

1. Reference Appropriate Documentation: Consult skill references for detailed guidance
2. Follow Swift Best Practices: Type safety, optionals, protocol-oriented design
3. Use Modern APIs: async/await, @Observable (iOS 17+), SwiftUI when possible
4. Test on Real Devices: Simulators don't catch all issues
5. Profile Early: Use Instruments to identify bottlenecks

Code Review Checklist

• Follows Swift style guidelines (naming, structure, access control)
• No force unwrapping (!) except in justified cases
• Proper memory management (no retain cycles, weak references where needed)
• UI updates on main thread (@MainActor or DispatchQueue.main)
• Error handling with proper Error types
• Accessibility labels and hints where appropriate
• Dynamic Type support for text
• Dark mode compatibility tested
• HIG compliance (spacing, colors, components)
• Performance profiled (no obvious leaks or slow operations)

Common Patterns

SwiftUI View with ViewModel

@MainActor
class UserViewModel: ObservableObject {
    @Published private(set) var users: [User] = []
    @Published private(set) var isLoading = false

    private let service: UserServiceProtocol

    init(service: UserServiceProtocol = UserService()) {
        self.service = service
    }

    func loadUsers() async {
        isLoading = true
        do {
            users = try await service.fetchUsers()
        } catch {
            // Handle error
        }
        isLoading = false
    }
}

struct UsersView: View {
    @StateObject private var viewModel = UserViewModel()

    var body: some View {
        Group {
            if viewModel.isLoading {
                ProgressView()
            } else {
                List(viewModel.users) { user in
                    UserRow(user: user)
                }
            }
        }
        .task {
            await viewModel.loadUsers()
        }
    }
}

Network Request with async/await

func fetchUser(id: String) async throws -> User {
    let url = URL(string: "https://api.example.com/users/\(id)")!
    let (data, response) = try await URLSession.shared.data(from: url)

    guard let httpResponse = response as? HTTPURLResponse,
          (200...299).contains(httpResponse.statusCode) else {
        throw NetworkError.serverError
    }

    return try JSONDecoder().decode(User.self, from: data)
}

Observable Model (iOS 17+)

@Observable
class ViewModel {
    var items: [Item] = []
    var isLoading = false

    func loadItems() async {
        isLoading = true
        items = await fetchItems()
        isLoading = false
    }
}

// In SwiftUI - automatically observes changes
struct ContentView: View {
    let viewModel = ViewModel()

    var body: some View {
        List(viewModel.items) { item in
            Text(item.name)
        }
    }
}

Platform-Specific Considerations

iOS

• Support multiple screen sizes (iPhone SE to Pro Max)
• Handle Dynamic Island on iPhone 14 Pro+
• Safe area insets for notch/home indicator
• Tab bar for 3-5 top-level sections
• Pull-to-refresh for content updates

macOS

• Menu bar with standard menus (App, File, Edit, View, Window, Help)
• Window management (resize, minimize, maximize)
• Keyboard shortcuts for all actions
• Toolbar customization
• Right-click context menus

iPad

• Support Split View and Slide Over multitasking
• Adapt layout for different sizes
• Keyboard shortcuts
• Pointer/trackpad support
• Drag and drop between apps

watchOS

• Glanceable information
• Large touch targets (full screen width)
• Digital Crown for scrolling
• Minimal text input

tvOS

• Focus-based navigation (Siri Remote)
• 10-foot viewing distance
• Large, clear text and images
• No touch interaction

Accessibility

Always implement:

• VoiceOver labels for images and controls
• Accessibility hints for complex interactions
• Dynamic Type support for all text
• Minimum 4.5:1 contrast for text
• Reduce Motion support for animations
• Keyboard navigation support (macOS)

Testing

• Unit tests for ViewModels and business logic
• UI tests for critical user flows
• Test on multiple devices and screen sizes
• Test in both light and dark mode
• Test with Dynamic Type at various sizes
• Test with VoiceOver enabled
• Profile with Instruments before release

Resources

This skill includes comprehensive reference documentation:

references/swift-best-practices.md

Complete Swift programming best practices covering code organization, type safety, optionals, protocol-oriented programming, modern Swift features, memory management, concurrency, and testing patterns.

references/swiftui-patterns.md

SwiftUI design patterns including view composition, state management, MVVM architecture, layout techniques, navigation patterns, animations, performance optimization, and accessibility.

references/human-interface-guidelines.md

Apple's Human Interface Guidelines covering design principles, platform conventions, typography, color, layout, components, accessibility, gestures, and platform-specific patterns for iOS, macOS, iPad, watchOS, and tvOS.

references/apple-frameworks.md

Comprehensive reference for Apple frameworks including Foundation, UIKit, AppKit, networking, Core Data, SwiftData, Combine, CloudKit, StoreKit, Core Location, MapKit, HealthKit, AVFoundation, and Core Animation.

references/performance-optimization.md

Performance optimization techniques covering app launch, memory management, CPU optimization, rendering, networking, battery efficiency, database performance, profiling with Instruments, and testing.