SwiftUI Animation (iOS 26+)

Review, write, and fix SwiftUI animations. Apply modern animation APIs with correct timing, transitions, and accessibility handling using Swift 6.2 patterns.

Triage Workflow

Step 1: Identify the animation category

Category	API	When to use
State-driven	withAnimation, .animation(_:value:)	Simple property 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() }

.animation(_:value:) (Implicit Animation)

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.

// WRONG: Manual AnimatableData (verbose, error-prone)
struct WaveShape: Shape, Animatable {
    var frequency: Double
    var amplitude: Double
    var phase: Double

    var animatableData: AnimatablePair<Double, AnimatablePair<Double, Double>> {
        get { AnimatablePair(frequency, AnimatablePair(amplitude, phase)) }
        set {
            frequency = newValue.first
            amplitude = newValue.second.first
            phase = newValue.second.second
        }
    }
    // ...
}

// CORRECT: @Animatable macro synthesizes animatableData
@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.

Common Mistakes

1. Animating without a value binding

// WRONG: .animation without value triggers on any state change
Text("Hello")
    .opacity(isVisible ? 1 : 0)
    .animation(.easeIn)

// CORRECT: Bind to the specific value
Text("Hello")
    .opacity(isVisible ? 1 : 0)
    .animation(.easeIn, value: isVisible)

2. Expensive work inside animation closures

// WRONG: Heavy computation every frame
.keyframeAnimator(initialValue: vals, trigger: t) { content, value in
    let filtered = applyExpensiveFilter(content)  // runs every frame
    return filtered.opacity(value.opacity)
} keyframes: { _ in /* ... */ }

// CORRECT: Precompute outside, animate only visual properties
.keyframeAnimator(initialValue: vals, trigger: t) { content, value in
    content.opacity(value.opacity)
} keyframes: { _ in /* ... */ }

3. Missing reduce motion support

// WRONG: Ignores accessibility setting
withAnimation(.bouncy) { showDetail = true }

// CORRECT: Respect reduce motion
@Environment(\.accessibilityReduceMotion) private var reduceMotion

withAnimation(reduceMotion ? .none : .bouncy) { showDetail = true }

4. Multiple matchedGeometryEffect sources

// WRONG: Both visible with same ID -- undefined behavior
HStack {
    Circle().matchedGeometryEffect(id: "dot", in: ns)
    Circle().matchedGeometryEffect(id: "dot", in: ns)
}

// CORRECT: Only one source visible at a time via conditional
if onLeft {
    Circle().matchedGeometryEffect(id: "dot", in: ns)
} else {
    Circle().matchedGeometryEffect(id: "dot", in: ns)
}

5. Using DispatchQueue or UIView.animate

// WRONG: UIKit patterns in SwiftUI
DispatchQueue.main.asyncAfter(deadline: .now() + 0.5) {
    withAnimation { isVisible = true }
}
UIView.animate(withDuration: 0.3) { /* ... */ }

// CORRECT: SwiftUI animation with delay
withAnimation(.spring.delay(0.5)) { isVisible = true }
withAnimation(.easeInOut(duration: 0.3)) { /* state change */ }

6. Forgetting animation on ContentTransition

// WRONG: No animation -- content transition has no effect
Text("\(count)")
    .contentTransition(.numericText(countsDown: true))

// CORRECT: Pair with animation modifier
Text("\(count)")
    .contentTransition(.numericText(countsDown: true))
    .animation(.snappy, value: count)

7. navigationTransition on wrong view

// WRONG: Applied inside a container
NavigationLink {
    VStack {
        DetailView(item: item)
            .navigationTransition(.zoom(sourceID: item.id, in: ns))
    }
} label: { /* ... */ }

// CORRECT: Applied on the outermost destination view
NavigationLink {
    DetailView(item: item)
        .navigationTransition(.zoom(sourceID: item.id, in: ns))
} label: { /* ... */ }

Review Checklist

• Animation curve matches intent (spring for natural, ease for mechanical)
• withAnimation wraps the state change, not the view
• .animation(_:value:) has an explicit value parameter
• matchedGeometryEffect has exactly one source per ID at a time
• Navigation zoom uses matching id and namespace on source and destination
• @Animatable macro used instead of manual animatableData
• accessibilityReduceMotion is checked and respected
• No heavy computation inside keyframe/phase content closures
• No DispatchQueue or UIView.animate for animation timing
• Transitions use .transition() on conditionally inserted views
• contentTransition is paired with .animation(_:value:)
• Symbol effects use correct category (discrete vs indefinite)
• Ensure animated state changes happen on @MainActor; types driving animations should be Sendable if passed across concurrency boundaries

Reference Material

• See references/animation-advanced.md for CustomAnimation protocol, full Spring variants, all Transition types, symbol effect details, Transaction system, UnitCurve types, and performance guidance.

API Verification

The apple-docs MCP server is available for verifying SwiftUI animation API names, signatures, and availability. Use searchAppleDocumentation with queries like "PhaseAnimator" or fetchAppleDocumentation with paths like /documentation/swiftui/animation to cross-check details when needed.