IOS Swiftui

iOS (SwiftUI) — Best Practices

AI Context & Token Optimization

1. SwiftUI Over UIKit: Strictly ban UIKit (unless bridging is unavoidable). Declarative SwiftUI trees are vastly more token-efficient and predictable for AI generation.
2. Modern Concurrency: Mandate async/await. Avoid completion handlers and closures, which lead to "callback hell" formatting that breaks AI syntax continuity.
3. Observable State: Use @Observable (iOS 17+) to keep state management clean and localized, preventing cross-file state hallucinations.

Project Structure

App/
├── App.swift            # @main struct
├── Core/                # Networking, Extensions, Utilities
├── Models/              # Data structures (Codable)
├── Views/               # SwiftUI Views
│   ├── Shared/          # Reusable components
│   └── Screens/         # Full page views
└── ViewModels/          # ObservableObjects for business logic

Naming Conventions

• Types/Structs/Classes: PascalCase (e.g., UserProfileView)
• Variables/Functions: camelCase (e.g., fetchUserData())
• Modifiers: Custom ViewModifiers should be PascalCase.

Architectural Patterns

• MVVM Pattern: Separate UI (View) from business logic (ViewModel). Views should only handle layout and state binding.
• State Management:
  • Use @State for simple, local UI state.
  • Use @StateObject (or @Observable macro in iOS 17+) for ViewModels owned by the view.
  • Use @EnvironmentObject (or @Environment) for global dependency injection.
• Networking: Use modern async/await (URLSession.shared.data(from:)). Avoid legacy closures/completion blocks.
• Concurrency: Use @MainActor on ViewModels to ensure UI updates happen on the main thread.

Universal DateTime Governance

• UTC at Rest: Store all Date values in UTC. Use ISO8601DateFormatter() with .withInternetDateTime and .withFractionalSeconds options for serialization.
• Clock Injection: Define a ClockProvider protocol with func now() -> Date. Default implementation returns Date(). Inject via @Environment or initializer. Banned: calling Date() directly in ViewModels or business logic.
• API Boundary: Transmit datetimes as epoch ms (Int64) or ISO-8601 UTC strings. Use JSONEncoder.DateEncodingStrategy.millisecondsSince1970 or custom DateFormatter.
• UI Display: Format with DateFormatter using explicit timeZone = TimeZone(secondsFromGMT: 0) for server times, then convert to user's local timezone. Never mix timezone-ambiguous Date objects.

Testing Strategies

• Framework: XCTest + XCUITest.
• Unit Tests: Test ViewModels independently of Views. Inject mock network clients via protocols to verify state changes.
• UI Tests: Use Accessibility Identifiers (.accessibilityIdentifier("login_btn")) to write stable UI tests.