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