IOS

Swift + SwiftUI iOS Development

When to activate

• Building iOS, iPadOS, or macOS apps with SwiftUI
• Implementing async/await networking with URLSession
• Setting up Core Data for local persistence
• Wiring Combine publishers and subscribers
• Preparing for App Store submission and review
• Debugging property wrapper selection (@State, @Binding, @ObservedObject, etc.)

When NOT to use

• UIKit-only projects where SwiftUI is explicitly excluded
• tvOS or watchOS targets with significantly different lifecycle
• Server-side Swift (Vapor, Hummingbird) without any UI layer

Instructions

Property Wrappers — When Each

// @State — local value owned by this view
struct ToggleRow: View {
    @State private var isOn = false

    var body: some View {
        Toggle("Notifications", isOn: $isOn)   // $ produces a Binding
    }
}

// @Binding — parent controls truth
struct ToggleRow: View {
    @Binding var isOn: Bool   // parent passes $parentState.isOn

    var body: some View {
        Toggle("Notifications", isOn: $isOn)
    }
}

// @StateObject — view owns and creates the object
struct ProfileView: View {
    @StateObject private var viewModel = ProfileViewModel()

    var body: some View {
        Text(viewModel.name)
    }
}

// @ObservedObject — object is passed in, owned elsewhere
struct ProfileView: View {
    @ObservedObject var viewModel: ProfileViewModel

    var body: some View {
        Text(viewModel.name)
    }
}

// @EnvironmentObject — injected at a high level, accessed anywhere below
struct UserBadge: View {
    @EnvironmentObject var session: UserSession

    var body: some View {
        Text(session.displayName)
    }
}

// Inject at root
ContentView().environmentObject(UserSession())

Rule: use @StateObject when the view creates the object. Use @ObservedObject when the object is injected. Never create an ObservableObject directly in the body property — it will be recreated on every render.

Async/Await with URLSession

// Models
struct User: Decodable {
    let id: Int
    let name: String
    let email: String
}

// Network layer
struct APIClient {
    let baseURL = URL(string: "https://api.example.com")!
    let decoder = JSONDecoder()

    func fetchUser(id: Int) async throws -> User {
        let url = baseURL.appendingPathComponent("users/\(id)")
        var request = URLRequest(url: url)
        request.setValue("Bearer \(TokenStore.current)", forHTTPHeaderField: "Authorization")

        let (data, response) = try await URLSession.shared.data(for: request)

        guard let http = response as? HTTPURLResponse else {
            throw URLError(.badServerResponse)
        }
        guard (200..<300).contains(http.statusCode) else {
            throw APIError.httpError(http.statusCode)
        }

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

// In a ViewModel
@MainActor
class UserViewModel: ObservableObject {
    @Published var user: User?
    @Published var error: Error?
    @Published var isLoading = false

    let client = APIClient()

    func load(id: Int) async {
        isLoading = true
        defer { isLoading = false }

        do {
            user = try await client.fetchUser(id: id)
        } catch {
            self.error = error
        }
    }
}

// In a SwiftUI view
struct UserView: View {
    @StateObject private var vm = UserViewModel()
    let userId: Int

    var body: some View {
        Group {
            if vm.isLoading {
                ProgressView()
            } else if let user = vm.user {
                Text(user.name)
            } else if let error = vm.error {
                Text("Error: \(error.localizedDescription)")
            }
        }
        .task { await vm.load(id: userId) }   // cancels automatically when view disappears
    }
}

Always mark ViewModels @MainActor to ensure @Published mutations happen on the main thread.

Core Data — NSPersistentContainer Setup

// Persistence.swift
import CoreData

struct PersistenceController {
    static let shared = PersistenceController()

    static var preview: PersistenceController = {
        let controller = PersistenceController(inMemory: true)
        let ctx = controller.container.viewContext
        // Insert sample data for previews
        let item = Item(context: ctx)
        item.timestamp = Date()
        try? ctx.save()
        return controller
    }()

    let container: NSPersistentContainer

    init(inMemory: Bool = false) {
        container = NSPersistentContainer(name: "MyApp")   // matches .xcdatamodeld filename

        if inMemory {
            container.persistentStoreDescriptions.first?.url = URL(fileURLWithPath: "/dev/null")
        }

        container.loadPersistentStores { _, error in
            if let error { fatalError("Core Data failed: \(error)") }
        }
        container.viewContext.automaticallyMergesChangesFromParent = true
        container.viewContext.mergePolicy = NSMergeByPropertyObjectTrumpMergePolicy
    }
}

// Inject at app entry point
@main
struct MyApp: App {
    let persistence = PersistenceController.shared

    var body: some Scene {
        WindowGroup {
            ContentView()
                .environment(\.managedObjectContext, persistence.container.viewContext)
        }
    }
}

// In a view
struct ItemList: View {
    @Environment(\.managedObjectContext) private var ctx

    @FetchRequest(
        sortDescriptors: [SortDescriptor(\.timestamp, order: .reverse)],
        animation: .default
    )
    private var items: FetchedResults<Item>

    func addItem() {
        let item = Item(context: ctx)
        item.timestamp = Date()
        try? ctx.save()
    }
}

For background operations, use container.newBackgroundContext() or container.performBackgroundTask { ctx in }.

Combine — sink and assign

import Combine

class SearchViewModel: ObservableObject {
    @Published var query = ""
    @Published var results: [Product] = []
    @Published var isLoading = false

    private var cancellables = Set<AnyCancellable>()
    private let api = APIClient()

    init() {
        $query
            .debounce(for: .milliseconds(300), scheduler: RunLoop.main)
            .removeDuplicates()
            .filter { $0.count >= 2 }
            .handleEvents(receiveOutput: { [weak self] _ in self?.isLoading = true })
            .flatMap { [weak self] q -> AnyPublisher<[Product], Never> in
                guard let self else { return Empty().eraseToAnyPublisher() }
                return self.api.search(query: q)
                    .catch { _ in Just([]) }
                    .eraseToAnyPublisher()
            }
            .receive(on: DispatchQueue.main)
            .handleEvents(receiveOutput: { [weak self] _ in self?.isLoading = false })
            .assign(to: &$results)           // assign(to:) with & ties lifetime to self, no cancellable needed
    }
}

Use .sink when you need side effects. Use .assign(to:) to drive a @Published property. Always store subscriptions in Set<AnyCancellable> or use the &$published form to avoid premature cancellation.

App Store Submission Checklist

Before submitting to App Store Connect:

Technical requirements:

• Build with the latest stable Xcode and latest iOS SDK
• Minimum deployment target set correctly in project settings
• No use of private APIs (App Store review scans for these)
• NSAppTransportSecurity exceptions documented and justified
• All required permission strings in Info.plist (camera, location, microphone, contacts, etc.)
• Icons for all required sizes present in asset catalog (Xcode generates from a 1024x1024 source)
• Launch screen or LaunchScreen.storyboard configured

Privacy:

• Privacy manifest (PrivacyInfo.xcprivacy) required for apps using specific APIs (file timestamp APIs, system boot time, disk space, active keyboard, user defaults)
• Third-party SDKs must also include privacy manifests
• Declare data collection in App Store Connect (Data Types used, linked to user, tracking)

App Store Connect:

• Version and build number incremented from last submission
• Screenshots for all required device sizes (6.9", 6.5", 5.5" iPhone; 13" and 12.9" iPad if iPad supported)
• App Preview video optional but improves conversion
• Keywords field: comma-separated, 100 character limit
• Age rating questionnaire completed
• Export Compliance: declare if using encryption (HTTPS qualifies; standard exemption usually applies)

Testing before submission:

• TestFlight beta tested on physical device, not only simulator
• Deep links and Universal Links tested
• Push notifications tested end-to-end
• In-app purchase sandbox flow verified
• Accessibility audit (VoiceOver, Dynamic Type)

Example

A settings screen demonstrating multiple property wrappers together:

@MainActor
class SettingsViewModel: ObservableObject {
    @Published var notificationsEnabled = false
    @Published var theme: AppTheme = .system

    func save() async {
        try? await UserPreferencesAPI.save(
            notifications: notificationsEnabled,
            theme: theme
        )
    }
}

struct SettingsView: View {
    @StateObject private var vm = SettingsViewModel()
    @EnvironmentObject var session: UserSession
    @Environment(\.dismiss) private var dismiss

    var body: some View {
        Form {
            Section("Account") {
                Text(session.email).foregroundStyle(.secondary)
            }
            Section("Preferences") {
                Toggle("Notifications", isOn: $vm.notificationsEnabled)
                Picker("Theme", selection: $vm.theme) {
                    ForEach(AppTheme.allCases) { Text($0.label).tag($0) }
                }
            }
        }
        .navigationTitle("Settings")
        .toolbar {
            ToolbarItem(placement: .confirmationAction) {
                Button("Done") {
                    Task {
                        await vm.save()
                        dismiss()
                    }
                }
            }
        }
    }
}