performance

Performance & Battery Audit

Scan for layout thrash, heavy animations, timers, and background tasks. Flag hotspots and suggest fixes.

When to use this skill

• Before App Store submission
• After adding complex animations or layouts
• When users report lag, jank, or battery drain
• When reviewing Views with frequent state changes

Quick Reference: Common Issues

Issue	Impact	Fix
GeometryReader in ScrollView	Layout thrash	Use containerRelativeFrame or cache sizes
Timer in View body	Battery drain	Use .onReceive with shared timer
Large images in List	Memory spike	Use LazyVStack, async image loading
Animation without value:	CPU/GPU	Scope animations with value: parameter
.drawingGroup() everywhere	GPU memory	Use only for complex overlapping content

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Step 1: Layout Performance Audit

1.1 GeometryReader Misuse

# GeometryReader (expensive layout pass)
rg --type swift -g '!*Tests*' 'GeometryReader' YourApp/Views/ | head -15

Issues: GeometryReader inside ScrollView/List causes relayout on scroll.

Fix (iOS 17+):

// ❌ Expensive
GeometryReader { geo in content.frame(width: geo.size.width * 0.8) }

// ✅ Modern alternative
content.containerRelativeFrame(.horizontal) { width, _ in width * 0.8 }

1.2 Layout Invalidation in Body

# Inline expensive object creation
rg --type swift -g '!*Tests*' 'DateFormatter\(\)|NumberFormatter\(\)|JSONDecoder\(\)' YourApp/Views/

Fix: Move to static/cached properties.

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Step 2: Animation Performance

2.1 Animation Scope

# Animations without value parameter (animate everything)
rg --type swift -g '!*Tests*' '\.animation\([^,)]+\)' YourApp/Views/ | grep -v 'value:' | head -15

Fix: Always scope animations:

.animation(.easeInOut, value: isExpanded)  // ✅ Only animates this change

2.2 Heavy/Repeating Animations

# Repeating animations (battery impact)
rg --type swift -g '!*Tests*' '\.repeatForever|\.repeat\(' YourApp/Views/

# Canvas/TimelineView (GPU intensive)
rg --type swift -g '!*Tests*' 'Canvas\s*\{|TimelineView' YourApp/Views/