Implement reactive state with Combine, Observation framework, and UDF patterns. Use when implementing state management with Combine, @Observable, or reactive patterns in iOS.
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---
name: ios-state-management
description: Implement reactive state with Combine, Observation framework, and UDF patterns. Use when implementing state management with Combine, @Observable, or reactive patterns in iOS.
metadata:
triggers:
files:
- '**/*.swift'
keywords:
- Observable
- "@Published"
- PassthroughSubject
- "@Observable"
- "@Namespace"
---
# iOS State Management
## **Priority: P0**
## Implementation Workflow
1. **Choose observation approach** — Use `@Observable` (iOS 17+) for modern SwiftUI; `Combine` with `@Published` for UIKit or broader compatibility.
2. **Expose state clearly** — Use UDF pattern: ViewModel exposes `Input` enum (events) and `Output` struct (state).
3. **Manage subscriptions** — Store Combine subscriptions in `Set<AnyCancellable>` with `.store(in: &cancellables)`.
4. **Dispatch to main thread** — Use `@MainActor` or `.receive(on: DispatchQueue.main)` for UI updates.
5. **Use exhaustive ViewState** — Prefer single `ViewState` enum (`.loading`, `.success(data)`, `.error(failure)`).
See [Combine and Observation framework examples](references/implementation.md)
## Anti-Patterns
- **No Uncleared Subscriptions**: Always use `.store(in: &cancellables)`
- **No Background UI Updates**: Use `.receive(on: .main)` or `@MainActor`
- **No Manual `objectWillChange.send()`**: Use `@Published` or `@Observable` instead
## References
- [Combine & Observation Setup](references/implementation.md)
