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swiftui-animation▌

dpearson2699/swift-ios-skills · updated Apr 8, 2026

$npx skills add https://github.com/dpearson2699/swift-ios-skills --skill swiftui-animation
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skill.md

SwiftUI Animation (iOS 26+)

Review, write, and fix SwiftUI animations. Apply modern animation APIs with correct timing, transitions, and accessibility handling using Swift 6.3 patterns.

Contents

Triage Workflow

Step 1: Identify the animation category

Category API When to use
State-driven withAnimation, .animation(_:body:), .animation(_:value:) Explicit state changes, selective modifier animation, or simple value-bound changes
Multi-phase PhaseAnimator Sequenced multi-step animations
Keyframe KeyframeAnimator Complex multi-property choreography
Shared element matchedGeometryEffect Layout-driven hero transitions
Navigation matchedTransitionSource + .navigationTransition(.zoom) NavigationStack push/pop zoom
View lifecycle .transition() Insertion and removal
Text content .contentTransition() In-place text/number changes
Symbol .symbolEffect() SF Symbol animations
Custom CustomAnimation protocol Novel timing curves

Step 2: Choose the animation curve

// Timing curves
.linear                              // constant speed
.easeIn(duration: 0.3)              // slow start
.easeOut(duration: 0.3)             // slow end
.easeInOut(duration: 0.3)           // slow start and end

// Spring presets (preferred for natural motion)
.smooth                              // no bounce, fluid
.smooth(duration: 0.5, extraBounce: 0.0)
.snappy                              // small bounce, responsive
.snappy(duration: 0.4, extraBounce: 0.1)
.bouncy                              // visible bounce, playful
.bouncy(duration: 0.5, extraBounce: 0.2)

// Custom spring
.spring(duration: 0.5, bounce: 0.3, blendDuration: 0.0)
.spring(Spring(duration: 0.6, bounce: 0.2), blendDuration: 0.0)
.interactiveSpring(response: 0.15, dampingFraction: 0.86)

Step 3: Apply and verify

  • Confirm animation triggers on the correct state change.
  • Test with Accessibility > Reduce Motion enabled.
  • Verify no expensive work runs inside animation content closures.

withAnimation (Explicit Animation)

withAnimation(.spring) { isExpanded.toggle() }

// With completion (iOS 17+)
withAnimation(.smooth(duration: 0.35), completionCriteria: .logicallyComplete) {
    isExpanded = true
} completion: { loadContent() }

Implicit Animation

Prefer .animation(_:body:) when only specific modifiers should animate. Use .animation(_:value:) for simple value-bound changes that can animate the view's animatable modifiers together.

Badge()
    .foregroundStyle(isActive ? .green : .secondary)
    .animation(.snappy) { content in
        content
            .scaleEffect(isActive ? 1.15 : 1.0)
            .opacity(isActive ? 1.0 : 0.7)
    }

Circle()
    .scaleEffect(isActive ? 1.2 : 1.0)
    .opacity(isActive ? 1.0 : 0.6)
    .animation(.bouncy, value: isActive)

Spring Type (iOS 17+)

Four initializer forms for different mental models.

// Perceptual (preferred)
Spring(duration: 0.5, bounce: 0.3)

// Physical
Spring(mass: 1.0, stiffness: 100.0, damping: 10.0)

// Response-based
Spring(response: 0.5, dampingRatio: 0.7)

// Settling-based
Spring(settlingDuration: 1.0, dampingRatio: 0.8)

Three presets mirror Animation presets: .smooth, .snappy, .bouncy.

PhaseAnimator (iOS 17+)

Cycle through discrete phases with per-phase animation curves.

enum PulsePhase: CaseIterable {
    case idle, grow, shrink
}

struct PulsingDot: View {
    var body: some View {
        PhaseAnimator(PulsePhase.allCases) { phase in
            Circle()
                .frame(width: 40, height: 40)
                .scaleEffect(phase == .grow ? 1.4 : 1.0)
                .opacity(phase == .shrink ? 0.5 : 1.0)
        } animation: { phase in
            switch phase {
            case .idle: .easeIn(duration: 0.2)
            case .grow: .spring(duration: 0.4, bounce: 0.3)
            case .shrink: .easeOut(duration: 0.3)
            }
        }
    }
}

Trigger-based variant runs one cycle per trigger change:

PhaseAnimator(PulsePhase.allCases, trigger: tapCount) { phase in
    // ...
} animation: { _ in .spring(duration: 0.4) }

KeyframeAnimator (iOS 17+)

Animate multiple properties along independent timelines.

struct AnimValues {
    var scale: Double = 1.0
    var yOffset: Double = 0.0
    var opacity: Double = 1.0
}

struct BounceView: View {
    @State private var trigger = false

    var body: some View {
        Image(systemName: "star.fill")
            .font(.largeTitle)
            .keyframeAnimator(
                initialValue: AnimValues(),
                trigger: trigger
            ) { content, value in
                content
                    .scaleEffect(value.scale)
                    .offset(y: value.yOffset)
                    .opacity(value.opacity)
            } keyframes: { _ in
                KeyframeTrack(\.scale) {
                    SpringKeyframe(1.5, duration: 0.3)
                    CubicKeyframe(1.0, duration: 0.4)
                }
                KeyframeTrack(\.yOffset) {
                    CubicKeyframe(-30, duration: 0.2)
                    CubicKeyframe(0, duration: 0.4)
                }
                KeyframeTrack(\.opacity) {
                    LinearKeyframe(0.6, duration: 0.15)
                    LinearKeyframe(1.0, duration: 0.25)
                }
            }
            .onTapGesture { trigger.toggle() }
    }
}

Keyframe types: LinearKeyframe (linear), CubicKeyframe (smooth curve), SpringKeyframe (spring physics), MoveKeyframe (instant jump).

Use repeating: true for looping keyframe animations.

@Animatable Macro

Replaces manual AnimatableData boilerplate. Attach to any type with animatable stored properties.

// Replaces manual AnimatableData boilerplate
@Animatable
struct WaveShape: Shape {
    var frequency: Double
    var amplitude: Double
    var phase: Double
    @AnimatableIgnored var lineWidth: CGFloat

    func path(in rect: CGRect) -> Path {
        // draw wave using frequency, amplitude, phase
    }
}

Rules:

  • Stored properties must conform to VectorArithmetic.
  • Use @AnimatableIgnored to exclude non-animatable properties.
  • Computed properties are never included.

matchedGeometryEffect (iOS 14+)

Synchronize geometry between views for shared-element animations.

struct HeroView: View {
    @Namespace private var heroSpace
    @State private var isExpanded = false

    var body: some View {
        if isExpanded {
            DetailCard()
                .matchedGeometryEffect(id: "card", in: heroSpace)
                .onTapGesture {
                    withAnimation(.spring(duration: 0.4, bounce: 0.2)) {
                        isExpanded = false
                    }
                }
        } else {
            ThumbnailCard()
                .matchedGeometryEffect(id: "card", in: heroSpace)
                .onTapGesture {
                    withAnimation(.spring(duration: 0.4, bounce: 0.2)) {
                        isExpanded = true
                    }
                }
        }
    }
}

Exactly one view per ID must be visible at a time for the interpolation to work.

Navigation Zoom Transition (iOS 18+)

Pair matchedTransitionSource on the source view with .navigationTransition(.zoom(...)) on the destination.

struct GalleryView: View {
    @Namespace private var zoomSpace
    let items: [GalleryItem]

    var body: some View {
        NavigationStack {
            ScrollView {
                LazyVGrid(columns: [GridItem(.adaptive(minimum: 100))]) {
                    ForEach(items) { item in
                        NavigationLink {
                            GalleryDetail(item: item)
                                .navigationTransition(
                                    .zoom(sourceID: item.id, in: zoomSpace)
                                )
                        } label: {
                            ItemThumbnail(item: item)
                                .matchedTransitionSource(
                                    id: item.id, in: zoomSpace
                                )
                        }
                    }
                }
            }
        }
    }
}

Apply .navigationTransition on the destination view, not on inner containers.

Transitions (iOS 17+)

Control how views animate on insertion and removal.

if showBanner {
    BannerView()
        .transition(.move(edge: .top).combined(with: .opacity))
}

Built-in types: .opacity, .slide, .scale, .scale(_:anchor:), .move(edge:), .push(from:), .offset(x:y:), .identity, .blurReplace, .blurReplace(_:), .symbolEffect, .symbolEffect(_:options:).

Asymmetric transitions:

.transition(.asymmetric(
    insertion: .push(from: .bottom),
    removal: .opacity
))

ContentTransition (iOS 16+)

Animate in-place content changes without insertion/removal.

Text("\(score)")
    .contentTransition(.numericText(countsDown: false))
    .animation(.snappy, value: score)

// For SF Symbols
Image(systemName: isMuted ? "speaker.slash" : "speaker.wave.3")
    .contentTransition(.symbolEffect(.replace.downUp))

Types: .identity, .interpolate, .opacity, .numericText(countsDown:), .numericText(value:), .symbolEffect.

Symbol Effects (iOS 17+)

Animate SF Symbols with semantic effects.

// Discrete (triggers on value change)
Image(systemName: "bell.fill")
    .symbolEffect(.bounce, value: notificationCount)

Image(systemName: "arrow.clockwise")
    .symbolEffect(.wiggle.clockwise, value: refreshCount)

// Indefinite (active while condition holds)
Image(systemName: "wifi")
    .symbolEffect(.pulse, isActive: isSearching)

Image(systemName: "mic.fill")
    .symbolEffect(.breathe, isActive: isRecording)

// Variable color with chaining
Image(systemName: "speaker.wave.3.fill")
    .symbolEffect(
        .variableColor.iterative.reversing.dimInactiveLayers,
        options: .repeating,
        isActive: isPlaying
    )

All effects: .bounce, .pulse, .variableColor, .scale, .appear, .disappear, .replace, .breathe, .rotate, .wiggle.

Scope: .byLayer, .wholeSymbol. Direction varies per effect.

Symbol Rendering Modes

Control how SF Symbol layers are colored with .symbolRenderingMode(_:).

Mode Effect When to use
.monochrome Single color applied uniformly (default) Toolbars, simple icons matching text
.hierarchical Single color with opacity layers for depth Subtle depth without multiple colors
.multicolor System-defined fixed colors per layer Weather, file types — Apple's intended palette
.palette Custom colors per layer via .foregroundStyle Brand colors, custom multi-color icons 
// Hierarchical — single tint, opacity layers for depth
Image(systemName: "speaker.wave.3.fill")
    .symbolRenderingMode(.hierarchical)
    .foregroundStyle(.blue)

// Palette — custom color per layer
Image(systemName: "person.crop.circle.badge.plus")
    .symbolRenderingMode(.palette)
    .foregroundStyle(.blue, .green)

// Multicolor — system-defined colors
Image(systemName: "cloud.sun.rain.fill")
    .symbolRenderingMode(.multicolor)

Variable color: .symbolVariableColor(value:) for percentage-based fill (signal strength, volume):

Image(systemName: "wifi")
    .symbolVariableColor(value: signalStrength) // 0.0–1.0

Docs: SymbolRenderingMode · symbolRenderingMode(_:)

Common Mistakes

1. Using bare .animation(_:) when you need precise scope

// TOO BROAD — applies when the view changes
.animation(.easeIn)

// CORRECT — bind animation to one value
.animation(.easeIn, value: isVisible)

// CORRECT — scope animation to selected modifiers
.animation(.easeIn) { content in
    content.opacity(isVisible ? 1.0 : 0.0)
}

2. Expensive work inside animation closures

Never run heavy computation in keyframeAnimator / PhaseAnimator content closures — they execute every frame. Precompute outside, animate only visual properties.

3. Missing reduce motion support

@Environment(\.accessibilityReduceMotion) private var reduceMotion
withAnimation(reduceMotion ? .none : .bouncy) { showDetail = true }

4. Multiple matchedGeometryEffect sources

Only one view per ID should be visible at a time. Two visible views with the same ID causes undefined layout.

5. Using DispatchQueue or UIView.animate

// WRONG
DispatchQueue.main.asyncAfter(deadline: .now() + 0.5) { withAnimation { isVisible = true } }
// CORRECT
withAnimation(.spring.delay(0.5)) { isVisible = true }

6. Forgetting animation on ContentTransition

// WRONG — no animation, content transition has no effect
Text("\(count)").contentTransition(.numericText(countsDown: true))
// CORRECT — pair with animation
Text("\(count)")
    .contentTransition(.numericText(countsDown: true))
    .animation(.snappy, value: count)

7. navigationTransition on wrong view

Apply .navigationTransition(.zoom(sourceID:in:)) on the outermost destination view, not inside a container.

Review Checklist

  • Animation curve matches intent (spring for natural, ease for mechanical)
  • withAnimation wraps the state change; implicit animation uses .animation(_:body:) for selective modifier scope or .animation(_:value:) with an explicit value
  • matchedGeometryEffect has exactly one source per ID; zoom uses matching id/namespace
  • @Animatable macro used instead of manual animatableData
  • accessibilityReduceMotion checked; no DispatchQueue/UIView.animate
  • Transitions use .transition(); contentTransition is paired with animation and uses the narrowest implicit animation scope that fits
  • Animated state changes on @MainActor; animation-driving types are Sendable

References