aRustyDev SwiftUI Architecture Patterns
Purpose
Architecture patterns for SwiftUI applications including MVVM, navigation, dependency injection, and the @Observable macro.
Patterns
MVVM with @Observable
import SwiftUI
// ViewModel using @Observable macro (iOS 17+/macOS 14+)
@Observable
final class ContentViewModel {
var items: [Item] = []
var isLoading = false
var errorMessage: String?
private let repository: ItemRepository
init(repository: ItemRepository = .live) {
self.repository = repository
}
func loadItems() async {
isLoading = true
defer { isLoading = false }
do {
items = try await repository.fetchAll()
} catch {
errorMessage = error.localizedDescription
}
}
}
// View
struct ContentView: View {
@State private var viewModel = ContentViewModel()
var body: some View {
List(viewModel.items) { item in
ItemRow(item: item)
}
.overlay {
if viewModel.isLoading {
ProgressView()
}
}
.task {
await viewModel.loadItems()
}
}
}
Dependency Injection
// Protocol-based dependency
protocol ItemRepository: Sendable {
func fetchAll() async throws -> [Item]
func save(_ item: Item) async throws
}
// Live implementation
struct LiveItemRepository: ItemRepository {
func fetchAll() async throws -> [Item] {
// Real implementation
}
func save(_ item: Item) async throws {
// Real implementation
}
}
// Mock for testing
struct MockItemRepository: ItemRepository {
var items: [Item] = []
var shouldFail = false
func fetchAll() async throws -> [Item] {
if shouldFail { throw TestError.fetchFailed }
return items
}
func save(_ item: Item) async throws {
// Mock save
}
}
// Static factory pattern
extension ItemRepository where Self == LiveItemRepository {
static var live: LiveItemRepository { LiveItemRepository() }
}
extension ItemRepository where Self == MockItemRepository {
static var mock: MockItemRepository { MockItemRepository() }
}
Navigation with NavigationStack
// Type-safe navigation paths
enum NavigationDestination: Hashable {
case detail(Item)
case settings
case profile(userId: String)
}
struct RootView: View {
@State private var path = NavigationPath()
var body: some View {
NavigationStack(path: $path) {
ContentView(path: $path)
.navigationDestination(for: NavigationDestination.self) { destination in
switch destination {
case .detail(let item):
ItemDetailView(item: item)
case .settings:
SettingsView()
case .profile(let userId):
ProfileView(userId: userId)
}
}
}
}
}
Environment-based Dependencies
// Environment key for repository
private struct ItemRepositoryKey: EnvironmentKey {
static let defaultValue: any ItemRepository = LiveItemRepository()
}
extension EnvironmentValues {
var itemRepository: any ItemRepository {
get { self[ItemRepositoryKey.self] }
set { self[ItemRepositoryKey.self] = newValue }
}
}
// Usage in view
struct ItemListView: View {
@Environment(\.itemRepository) private var repository
@State private var items: [Item] = []
var body: some View {
List(items) { item in
Text(item.name)
}
.task {
items = try? await repository.fetchAll() ?? []
}
}
}
// Preview with mock
#Preview {
ItemListView()
.environment(\.itemRepository, MockItemRepository(items: .preview))
}
File Organization
Feature-Based Structure (Recommended)
MyApp/
├── App/
│ ├── MyApp.swift # @main entry point
│ ├── AppDelegate.swift # UIKit lifecycle (if needed)
│ └── AppState.swift # Global @Observable state
│
├── Features/ # Feature modules
│ ├── Home/
│ │ ├── Views/
│ │ │ ├── HomeView.swift
│ │ │ └── HomeCard.swift
│ │ ├── ViewModels/
│ │ │ └── HomeViewModel.swift
│ │ └── Models/
│ │ └── HomeItem.swift
│ │
│ ├── Profile/
│ │ ├── Views/
│ │ ├── ViewModels/
│ │ └── Models/
│ │
│ └── Settings/
│ └── ...
│
├── Core/ # Shared infrastructure
│ ├── Repositories/
│ │ └── ItemRepository.swift
│ ├── Services/
│ │ ├── Network/
│ │ │ ├── APIClient.swift
│ │ │ ├── Endpoints.swift
│ │ │ └── NetworkError.swift
│ │ └── Persistence/
│ │ ├── DatabaseManager.swift
│ │ └── KeychainService.swift
│ └── Extensions/
│ ├── View+Extensions.swift
│ └── Date+Extensions.swift
│
├── Shared/ # Reusable UI components
│ ├── Components/
│ │ ├── LoadingView.swift
│ │ ├── ErrorView.swift
│ │ └── AsyncButton.swift
│ ├── Modifiers/
│ │ ├── CardStyle.swift
│ │ └── ShimmerEffect.swift
│ └── Styles/
│ └── ButtonStyles.swift
│
├── Utilities/ # Helpers and constants
│ ├── Constants.swift
│ ├── Logger.swift
│ └── Formatters.swift
│
├── Resources/
│ ├── Assets.xcassets # Images and colors
│ ├── Localizable.xcstrings # Localized strings (Xcode 15+)
│ └── Fonts/ # Custom fonts
│ └── CustomFont.ttf
│
└── Tests/
├── UnitTests/
│ ├── ViewModels/
│ │ └── HomeViewModelTests.swift
│ └── Services/
│ └── APIClientTests.swift
└── UITests/
├── HomeUITests.swift
└── Helpers/
└── XCUIApplication+Extensions.swift
Swift Package Structure
MyAppPackage/
├── Package.swift
├── Sources/
│ ├── MyApp/ # Main app target
│ │ └── MyApp.swift
│ ├── Features/ # Feature library
│ │ ├── Home/
│ │ └── Profile/
│ ├── Core/ # Core library
│ │ ├── Networking/
│ │ └── Persistence/
│ └── SharedUI/ # UI components library
│ ├── Components/
│ └── Modifiers/
└── Tests/
├── CoreTests/
└── FeaturesTests/
Best Practices
- Use @Observable for ViewModels - Simpler than ObservableObject
- Inject dependencies via init - Enables testing
- Use NavigationStack for navigation - Type-safe, deep-linkable
- Keep views small - Extract subviews early
- Use task modifier for async - Proper lifecycle management
Related Skills
- swiftui-data-flow: State management details
- swiftui-components: UI elements and layouts
- swiftui-gestures: User interactions
- swiftui-testing: Testing these patterns
- swift-concurrency: Async/await patterns