iOS Animation Code Review#

Quick Reference#

Issue TypeReferenceSpring parameters, withAnimation misuse, phase/keyframe bugsreferences/swiftui-animation-patterns.mdFrame drops, offscreen rendering, main thread blockingreferences/performance.mdReduce Motion, VoiceOver, motion sensitivityreferences/accessibility.mdTransition protocol, matchedGeometryEffect, navigation transitionsreferences/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.

StepWhat you doPass condition (objective)1. InventoryList 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. AnchorRe-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. EvidenceFor 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. ReportEmit 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:

text

[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#

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?