ios-animation-code-review

name

ios-animation-code-review

description

Reviews iOS animation code for correctness, performance, accessibility, and Apple API best practices. Use when reviewing .swift files containing animation code — withAnimation, .animation(), PhaseAnimator, KeyframeAnimator, matchedGeometryEffect, navigationTransition, CABasicAnimation, CASpringAnimation, UIViewPropertyAnimator, UIDynamicAnimator, symbolEffect, scrollTransition, contentTransition, or custom Transition conformances.

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

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)

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

1. 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?
2. Is this custom animation necessary, or does the system already provide it (standard transitions, SF Symbol effects, Liquid Glass)?
3. Could this animation cause frame drops — is it animating expensive properties (blur, shadow without path, mask) in a list or scroll view?
4. Are all animations interruptible? Can the user act without waiting for completion? Does gesture-driven feedback follow spatial expectations?
5. Is withAnimation scoped to the minimal state change needed, or is it wrapping unrelated mutations?
6. For matchedGeometryEffect — are source and destination using the same ID and namespace, and is only one visible at a time?