swiftui-performance-inspector

SwiftUI Performance Inspector

Diagnose from code first, then request profiling evidence when code review cannot explain the symptom.

Workflow

1. Classify the symptom: slow rendering, scrolling jank, high CPU, memory growth, hangs, broad updates, or layout thrash.
2. If code is available, review with references/code-smells.md.
3. If code is missing, ask for the smallest useful slice: target view, data flow, reproduction steps, device/simulator, build config, and deployment target.
4. If runtime evidence is needed, use references/profiling-intake.md for the exact Instruments checklist.
5. Report likely causes, evidence, fixes, and validation steps using references/report-template.md when useful.

Code Review Focus

• invalidation storms from broad observation or environment reads
• unstable identity in List/ForEach
• heavy derived work in body or view builders
• layout thrash from complex hierarchy, GeometryReader, or preferences
• main-thread image decode/resize or other expensive work
• animation and transition work applied too broadly

Profiling Evidence

Ask for SwiftUI timeline or Time Profiler export/screenshots, device/OS/build configuration, exact profiled interaction, and before/after metrics when comparing changes.

Map evidence to invalidation, identity churn, layout, main-thread work, image cost, animation cost, or hangs. Distinguish trace-backed findings from code-level suspicion and state what evidence would reduce uncertainty.

Fix Defaults

• narrow state scope and observation fan-out
• stabilize list identities
• move heavy work out of body into model/service precomputation, memoized helpers, background preprocessing, or input-driven derived state
• use @State only for view-owned state, not arbitrary caches
• use equatable() only when equality is cheaper than recomputing and inputs are value-semantic
• downsample images before rendering
• reduce layout complexity or add stable sizing where appropriate

Output

Provide a short metrics table when available, top issues ordered by impact, proposed fixes with effort, and verification steps.

References

• references/profiling-intake.md
• references/code-smells.md
• references/report-template.md
• references/optimizing-swiftui-performance-instruments.md
• references/understanding-improving-swiftui-performance.md
• references/understanding-hangs-in-your-app.md
• references/demystify-swiftui-performance-wwdc23.md

Use current Apple Developer docs when Instruments or SwiftUI performance guidance may have changed.