1# Optimizing SwiftUI Performance with Instruments (Summary)
2 
3Context: WWDC session introducing the next-generation SwiftUI Instrument in Instruments 26 and how to diagnose SwiftUI-specific bottlenecks.
4 
5## Key takeaways
6 
7- Profile SwiftUI issues with the SwiftUI template (SwiftUI instrument + Time Profiler + Hangs/Hitches).
8- Long view body updates are a common bottleneck; use "Long View Body Updates" to identify slow bodies.
9- Set inspection range on a long update and correlate with Time Profiler to find expensive frames.
10- Keep work out of `body`: move formatting, sorting, image decoding, and other expensive work into cached or precomputed paths.
11- Use Cause & Effect Graph to diagnose *why* updates occur; SwiftUI is declarative, so backtraces are often unhelpful.
12- Avoid broad dependencies that trigger many updates (e.g., `@Observable` arrays or global environment reads).
13- Prefer granular view models and scoped state so only the affected view updates.
14- Environment values update checks still cost time; avoid placing fast-changing values (timers, geometry) in environment.
15- Profile early and often during feature development to catch regressions.
16 
17## Suggested workflow (condensed)
18 
191. Record a trace in Release mode using the SwiftUI template.
202. Inspect "Long View Body Updates" and "Other Long Updates."
213. Zoom into a long update, then inspect Time Profiler for hot frames.
224. Fix slow body work by moving heavy logic into precomputed/cache paths.
235. Use Cause & Effect Graph to identify unintended update fan-out.
246. Re-record and compare the update counts and hitch frequency.
25 
26## Example patterns from the session
27 
28- Caching formatted distance strings in a location manager instead of computing in `body`.
29- Replacing a dependency on a global favorites array with per-item view models to reduce update fan-out.
30