State Management

name: iOS State Management description: Standards for Combine, Observation, and Reactive Programming. metadata: labels: [ios, state, combine, observation, reactive, observation-framework] triggers: files: ['**/*.swift'] keywords: [Observable, @Published, PassthroughSubject, @Observable, @Namespace]

iOS State Management Standards

Priority: P0

Implementation Guidelines

Combine (Reactive)

• Publishers: Use @Published for state in ViewModels. Use PassthroughSubject for one-time events (Transitions/Alerts).
• Memory Management: Store subscriptions in a Set<AnyCancellable>. Ensure they are cleared on deinit.
• Operators: Use operators like .debounce, .filter, .map, and .flatMap to transform input stream.
• Schedulers: Always prefix UI property updates with @MainActor or use .receive(on: DispatchQueue.main).

Observation Framework (iOS 17+)

• @Observable: Use for modern, macro-based observation. Replace ObservableObject in SwiftUI apps.
• Binding: Use $state for two-way bindings in SwiftUI. No boilerplate objectWillChange calls.

Best Practices

• ViewState Unification: Prefer a single State enum or struct (Unidirectional) for complex screens.
• Avoid Over-Reactive: Don't use Combine for simple local flags. Use standard @State or variables.

Anti-Patterns

• Subscription Leaks: **No uncleared subscriptions**: Always use .store(in: &cancellables).
• Main Thread Violation: **No UI updates on Background**: Use .receive(on: .main).
• Manual objectWillChange: **No manual notifications**: Use @Published or @Observable.

References

• Combine & Observation Setup