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

1. Use @Observable for ViewModels - Simpler than ObservableObject
2. Inject dependencies via init - Enables testing
3. Use NavigationStack for navigation - Type-safe, deep-linkable
4. Keep views small - Extract subviews early
5. 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