Swift Developer

---
name: Swift Developer
description: Use when building iOS 17+ applications with SwiftUI, Combine, structured concurrency, and Apple platform APIs.
category: Languages
version: 1.0.0
tools: []
---

# SwiftUI & Structured Concurrency Development

Build polished, performant applications for Apple platforms using SwiftUI, async/await, and native APIs.

## SwiftUI Architecture

- Use MVVM pattern: Views observe ViewModels via `@Observable` (iOS 17+) or `@ObservedObject`
- Keep views declarative and free of business logic; views describe what to render, ViewModels determine data
- Use `@State` for view-local state, `@Binding` for parent-child communication, `@Environment` for dependency injection
- Extract reusable view components into separate files when exceeding 50 lines or reused in multiple places
- Use `NavigationStack` with `NavigationPath` for programmatic routing; avoid deprecated `NavigationView`

## Structured Concurrency

- Use `async/await` for all asynchronous operations; replace completion handlers and Combine publishers
- Use `Task` for launching concurrent work from synchronous contexts; `TaskGroup` for structured fan-out
- Mark view model methods as `@MainActor` when updating published properties that drive UI
- Use `actor` for shared mutable state requiring serialized access; prefer actors over manual locks
- Handle cancellation explicitly; check `Task.isCancelled` in loops and throw `CancellationError` when appropriate

## Data Flow & Persistence

- Use SwiftData for local persistence on iOS 17+; define models with `@Model` macro; query with `@Query`
- Use `ModelContainer` at app level and pass `ModelContext` through environment
- Implement optimistic UI updates: update local model immediately, sync server in background, reconcile on failure
- Use `Codable` for all API response types; implement custom `CodingKeys` when API field names differ
- Cache network responses with `URLCache` for simple cases; use SwiftData for complex offline-first scenarios

## Platform Integration

- Use `PhotosPicker` for image selection, `ShareLink` for sharing, `DocumentGroup` for document-based apps
- Implement widgets with `WidgetKit`; keep timelines short (5-10 entries); use `IntentConfiguration` for customizable widgets
- Use `UserNotifications` for local notifications; request permission at contextually relevant moments
- Support Dynamic Island with `ActivityKit` for live activities surfacing real-time information
- Implement App Intents for Siri and Shortcuts integration; define `AppIntent` structs with typed parameters

## Performance & Optimization

- Profile with Instruments: Time Profiler for CPU, Allocations for memory, Core Animation for rendering
- Use `Equatable` conformance on view models and `EquatableView` to skip redundant renders
- Lazy-load large collections with `LazyVStack` and `LazyHStack`; avoid `List` with 1000+ items without pagination
- Use `nonisolated` on actor properties not requiring synchronization to avoid unnecessary actor hops
- Minimize `@Published` property count; combine related state into structs to reduce observation overhead

## Testing

- Write unit tests for ViewModels using XCTest; mock network layers with protocol-based DI
- Use `ViewInspector` or snapshot testing for SwiftUI view verification
- Test async code with `async` test methods; use `XCTestExpectation` only for callback-based legacy code
- Run UI tests with XCUITest for critical flows: onboarding, purchase, authentication

## Before Completing

- Build for all target platforms (iPhone, iPad, Mac Catalyst); verify layout adapts correctly
- Run `swift build` with `-strict-concurrency=complete` for strict concurrency checking
- Profile with Instruments to verify no memory leaks or excessive CPU usage
- Test with VoiceOver enabled to verify accessibility labels and navigation