iOS Animation Code Review Skill

iOS Animation Code Review

Quick Reference

| Issue Type | Reference | |------------|-----------| | Spring parameters, withAnimation misuse, phase/keyframe bugs | references/swiftui-animation-patterns.md | | Frame drops, offscreen rendering, main thread blocking | references/performance.md | | Reduce Motion, VoiceOver, motion sensitivity | references/accessibility.md | | Transition protocol, matchedGeometryEffect, navigation transitions | references/transitions.md |

Hard gates (sequence)

Complete in order for the files in scope. If a step fails, omit the finding, re-anchor, or downgrade to a question—do not ship accusations without meeting the pass condition.

| Step | What you do | Pass condition (objective) | |------|-------------|----------------------------| | 1. Inventory | List each file under review and where animation APIs appear (line ranges or symbol names: withAnimation, .animation, matchedGeometryEffect, PhaseAnimator, UIKit/CA animators, etc.). | A written list exists; files with no animation APIs are explicitly marked out of scope. | | 2. Anchor | Re-read the cited region in the current file or diff hunk before naming an issue. | Each [FILE:LINE] still shows the behavior; stale line numbers are fixed or the finding is dropped. | | 3. Evidence | For framework-specific claims (spring curves, Transition conformance, Reduce Motion), cross-check the matching row in Quick Reference against references/*.md. | The finding’s detail names the reference file used, or states inline-only (structural/readability with no framework rule). | | 4. Report | Emit findings using Output Format. | Headers match [FILE:LINE] ISSUE_TITLE; checklist items below are applied only where gates 1–2 covered that code. |

Output Format

Report each finding as:

[FILE:LINE] ISSUE_TITLE

Example: [AnimatedCard.swift:42] Missing Reduce Motion fallback for spring animation

All details, code suggestions, and rationale follow after the header line.

Review Checklist

[ ] @Environment(\.accessibilityReduceMotion) checked — animations have Reduce Motion fallback
[ ] Animation is not the sole feedback channel — important state changes pair with haptics (.sensoryFeedback) or audio
[ ] Custom animation isn't duplicating system-provided motion (standard nav transitions, sheet presentation, SF Symbol effects)
[ ] Animations on frequent interactions are brief and unobtrusive — or absent (system handles it)
[ ] All animations are interruptible — user is never forced to wait for completion before interacting
[ ] Spring animations use duration/bounce parameters (not raw mass/stiffness/damping unless UIKit/CA)
[ ] No deprecated .animation() without value: parameter
[ ] withAnimation wraps state changes, not view declarations
[ ] matchedGeometryEffect IDs are stable and unique within the namespace
[ ] geometryGroup() used when parent geometry animates with child views appearing
[ ] Looping animations (PhaseAnimator, symbolEffect) have finite phases or appropriate trigger
[ ] No CATransaction.setAnimationDuration() in UIView-backed layers (use UIView.animate instead)
[ ] Interactive animations handle interruption (re-trigger mid-flight doesn't break state)
[ ] Shadow animations provide explicit shadowPath (avoids per-frame recalculation)
[ ] Gesture-driven animations preserve velocity on release for natural completion
[ ] Gesture-driven feedback follows spatial expectations (dismiss direction matches reveal direction)
[ ] No animation of .id() modifier (destroys view identity — use transition or matchedGeometryEffect instead)

When to Load References

Incorrect spring setup or withAnimation scope issues → swiftui-animation-patterns.md
Hitches, dropped frames, or expensive animations in scroll views → performance.md
Missing Reduce Motion handling or motion accessibility → accessibility.md
matchedGeometryEffect glitches or custom Transition bugs → transitions.md

Review Questions

Does every animation have a Reduce Motion fallback that preserves the information conveyed? Is animation the only feedback channel, or are haptics/audio supplementing it?
Is this custom animation necessary, or does the system already provide it (standard transitions, SF Symbol effects, Liquid Glass)?
Could this animation cause frame drops — is it animating expensive properties (blur, shadow without path, mask) in a list or scroll view?
Are all animations interruptible? Can the user act without waiting for completion? Does gesture-driven feedback follow spatial expectations?
Is withAnimation scoped to the minimal state change needed, or is it wrapping unrelated mutations?
For matchedGeometryEffect — are source and destination using the same ID and namespace, and is only one visible at a time?

Agent Skills: iOS Animation Code Review

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