activitykit

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

1. Activities are temporary. Max 8 hours (12 with stale date). Not for persistent content.
2. Updates come from app or push. Use ActivityKit in-app for local updates, push notifications for server-driven updates.
3. Widget extension renders the UI. Live Activities share the widget extension target.
4. Dynamic Island has 4 presentations. Compact leading, compact trailing, expanded, minimal. Design for all.
5. Push tokens change. Observe token updates and send new tokens to your server.
6. End activities explicitly. Don't rely on timeout — end when the activity completes.
7. Content state must be small. Encode to < 4KB for push updates.
8. 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