ios-animation-code-review（iOS animation 代码审查）

iOS Animation Code Review

Quick Reference

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

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?