By name: activitykit description: Use when implementing or reviewing Live Activities, Dynamic Island, Lock Screen presentations, or ActivityKit updates.
ActivityKit / Live Activities
Review and write ActivityKit code for correct activity lifecycle, push updates, and presentation layouts.
Responsibility
Owns: Activity class, ActivityAttributes, ActivityContent, start/update/end lifecycle, ActivityKit push notifications, push token management, Dynamic Island layouts (compact/expanded/minimal), Lock Screen presentation, stale dates, alert configurations.
Does NOT own: Widget timeline mechanisms (WidgetKit), UI design (SwiftUI skill), push notification infrastructure (server-side), AlarmKit integration.
Core Principles
- Activities are temporary. Max 8 hours (12 with stale date). Not for persistent content.
- Updates come from app or push. Use ActivityKit in-app for local updates, push notifications for server-driven updates.
- Widget extension renders the UI. Live Activities share the widget extension target.
- Dynamic Island has 4 presentations. Compact leading, compact trailing, expanded, minimal. Design for all.
- Push tokens change. Observe token updates and send new tokens to your server.
- End activities explicitly. Don't rely on timeout — end when the activity completes.
- Content state must be small. Encode to < 4KB for push updates.
- NSSupportsLiveActivities required. Set to true in Info.plist.
Red Flags
| Anti-Pattern | Problem | Fix |
|---|---|---|
| No NSSupportsLiveActivities | Activities fail silently | Add to Info.plist |
| Content state > 4KB | Push updates rejected | Keep state minimal |
| Not observing push token changes | Server has stale token | Observe Activity.pushTokenUpdates |
| Not ending completed activities | Stale content on Lock Screen | Call activity.end() |
| Complex layouts in minimal presentation | Truncated/unreadable | Keep minimal to icon + small text |
References
references/activitykit-patterns.md— Attributes, lifecycle, push tokens, Dynamic Island layouts, constraints