# iOS Swift Patterns

Production-grade iOS development with Swift, SwiftUI, and UIKit.

## Architecture

### MVVM + Coordinator Pattern
```
View (SwiftUI/UIViewController)
  ↕ binds to
ViewModel (ObservableObject)
  ↕ calls
Service Layer (Networking, DB)
  ↕
Core Data / API
```

### Key Principles
- **Views are dumb**: They render state and forward actions — no business logic
- **ViewModels own state**: `@Published` properties, `@State` only for local UI
- **Services are stateless**: Network calls, DB operations, analytics
- **Coordinators handle navigation**: Removing navigation from views makes them reusable

## SwiftUI Best Practices

### Performance
- Use `LazyVStack`/`LazyHStack` for large lists, not `VStack`
- Mark views with `@MainActor` explicitly
- Use `equatable()` on complex views to prevent unnecessary re-renders
- Prefer `@State` for local, `@StateObject` for owned, `@ObservedObject` for passed-in

### State Management
```swift
// Good: Clear separation
@MainActor
class UserViewModel: ObservableObject {
    @Published var users: [User] = []
    @Published var isLoading = false

    func loadUsers() async {
        isLoading = true
        users = await userService.fetchUsers()
        isLoading = false
    }
}
```

## App Store Submission Checklist
- [ ] No Hardcoded API keys
- [ ] TestFlight beta tested with real users
- [ ] Privacy manifest updated
- [ ] Screenshots for all required sizes
- [ ] App Store description and keywords ready
- [ ] Subscription/IAP products configured

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> Source: [cosmicstack-labs/mercury-agent-skills](https://github.com/cosmicstack-labs/mercury-agent-skills) — distributed by [TomeVault](https://tomevault.io).
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