swiftui-gestures（swiftui gestures 命令行）

SwiftUI Gestures (iOS 26+)

Review, write, and fix SwiftUI gesture interactions. Apply modern gesture APIs with correct composition, state management, and conflict resolution using Swift 6.3 patterns.

Contents

• Gesture Overview
• TapGesture
• LongPressGesture
• DragGesture
• MagnifyGesture (iOS 17+)
• RotateGesture (iOS 17+)
• Gesture Composition
• @GestureState
• Adding Gestures to Views
• Custom Gesture Protocol
• Common Mistakes
• Review Checklist
• References

Gesture Overview

Discrete gestures fire once (.onEnded). Continuous gestures stream updates (.onChanged, .onEnded, .updating).

TapGesture

Recognizes one or more taps. Use the count parameter for multi-tap.

// Single, double, and triple tap
TapGesture()            .onEnded { tapped.toggle() }
TapGesture(count: 2)    .onEnded { handleDoubleTap() }
TapGesture(count: 3)    .onEnded { handleTripleTap() }

// Shorthand modifier
Text("Tap me").onTapGesture(count: 2) { handleDoubleTap() }

LongPressGesture

Succeeds after the user holds for minimumDuration. Fails if finger moves beyond maximumDistance.

// Basic long press (0.5s default)
LongPressGesture()
    .onEnded { _ in showMenu = true }

// Custom duration and distance tolerance
LongPressGesture(minimumDuration: 1.0, maximumDistance: 10)
    .onEnded { _ in triggerHaptic() }

With visual feedback via @GestureState + .updating():

@GestureState private var isPressing = false

Circle()
    .fill(isPressing ? .red : .blue)
    .scaleEffect(isPressing ? 1.2 : 1.0)
    .gesture(
        LongPressGesture(minimumDuration: 0.8)
            .updating($isPressing) { current, state, _ in state = current }
            .onEnded { _ in completedLongPress = true }
    )

Shorthand: .onLongPressGesture(minimumDuration:perform:onPressingChanged:).

DragGesture

Tracks finger movement. Value provides startLocation, location, translation, velocity, and predictedEndTranslation.

@State private var offset = CGSize.zero

RoundedRectangle(cornerRadius: 16)
    .fill(.blue)
    .frame(width: 100, height: 100)
    .offset(offset)
    .gesture(
        DragGesture()
            .onChanged { value in offset = value.translation }
            .onEnded { _ in withAnimation(.spring) { offset = .zero } }
    )

Configure minimum distance and coordinate space:

DragGesture(minimumDistance: 20, coordinateSpace: .global)

MagnifyGesture (iOS 17+)

Replaces the deprecated MagnificationGesture. Tracks pinch-to-zoom scale.

@GestureState private var magnifyBy = 1.0

Image("photo")
    .resizable().scaledToFit()
    .scaleEffect(magnifyBy)
    .gesture(
        MagnifyGesture()
            .updating($magnifyBy) { value, state, _ in
                state = value.magnification
            }
    )

With persisted scale:

@State private var currentScale = 1.0
@GestureState private var gestureScale = 1.0

Image("photo")
    .scaleEffect(currentScale * gestureScale)
    .gesture(
        MagnifyGesture(minimumScaleDelta: 0.01)
            .updating($gestureScale) { value, state, _ in state = value.magnification }
            .onEnded { value in
                currentScale = min(max(currentScale * value.magnification, 0.5), 5.0)
            }
    )

RotateGesture (iOS 17+)

RotateGesture is the newer alternative to RotationGesture. Tracks two-finger rotation angle.

@State private var angle = Angle.zero

Rectangle()
    .fill(.blue).frame(width: 200, height: 200)
    .rotationEffect(angle)
    .gesture(
        RotateGesture(minimumAngleDelta: .degrees(1))
            .onChanged { value in angle = value.rotation }
    )

With persisted rotation:

@State private var currentAngle = Angle.zero
@GestureState private var gestureAngle = Angle.zero

Rectangle()
    .rotationEffect(currentAngle + gestureAngle)
    .gesture(
        RotateGesture()
            .updating($gestureAngle) { value, state, _ in state = value.rotation }
            .onEnded { value in currentAngle += value.rotation }
    )

Gesture Composition

.simultaneously(with:) — both gestures recognized at the same time

let magnify = MagnifyGesture()
    .onChanged { value in scale = value.magnification }

let rotate = RotateGesture()
    .onChanged { value in angle = value.rotation }

Image("photo")
    .scaleEffect(scale)
    .rotationEffect(angle)
    .gesture(magnify.simultaneously(with: rotate))

The value is SimultaneousGesture.Value with .first and .second optionals.

.sequenced(before:) — first must succeed before second begins

let longPressBeforeDrag = LongPressGesture(minimumDuration: 0.5)
    .sequenced(before: DragGesture())
    .onEnded { value in
        guard case .second(true, let drag?) = value else { return }
        finalOffset.width += drag.translation.width
        finalOffset.height += drag.translation.height
    }

.exclusively(before:) — only one succeeds (first has priority)

let doubleTapOrLongPress = TapGesture(count: 2)
    .map { ExclusiveResult.doubleTap }
    .exclusively(before:
        LongPressGesture()
            .map { _ in ExclusiveResult.longPress }
    )
    .onEnded { result in
        switch result {
        case .first(let val): handleDoubleTap()
        case .second(let val): handleLongPress()
        }
    }

@GestureState

@GestureState is a property wrapper that automatically resets to its initial value when the gesture ends. Use for transient feedback; use @State for values that persist.

@GestureState private var dragOffset = CGSize.zero  // resets to .zero
@State private var position = CGSize.zero            // persists

Circle()
    .offset(
        x: position.width + dragOffset.width,
        y: position.height + dragOffset.height
    )
    .gesture(
        DragGesture()
            .updating($dragOffset) { value, state, _ in
                state = value.translation
            }
            .onEnded { value in
                position.width += value.translation.width
                position.height += value.translation.height
            }
    )

Custom reset with animation: @GestureState(resetTransaction: Transaction(animation:.spring))

Adding Gestures to Views

Three modifiers control gesture priority in the view hierarchy:

// Problem: parent tap swallows child tap
VStack {
    Button("Child") { handleChild() }  // never fires
}
.gesture(TapGesture().onEnded { handleParent() })

// Fix 1: Use simultaneousGesture on parent
VStack {
    Button("Child") { handleChild() }
}
.simultaneousGesture(TapGesture().onEnded { handleParent() })

// Fix 2: Give parent explicit priority
VStack {
    Text("Child")
        .gesture(TapGesture().onEnded { handleChild() })
}
.highPriorityGesture(TapGesture().onEnded { handleParent() })

GestureMask

Control which gestures participate when using .gesture(_:including:):

.gesture(drag, including: .gesture)   // only this gesture, not subviews
.gesture(drag, including: .subviews)  // only subview gestures
.gesture(drag, including: .all)       // default: this + subviews

Custom Gesture Protocol

Create reusable gestures by conforming to Gesture:

struct SwipeGesture: Gesture {
    enum Direction { case left, right, up, down }
    let minimumDistance: CGFloat
    let onSwipe: (Direction) -> Void

    init(minimumDistance: CGFloat = 50, onSwipe: @escaping (Direction) -> Void) {
        self.minimumDistance = minimumDistance
        self.onSwipe = onSwipe
    }

    var body: some Gesture {
        DragGesture(minimumDistance: minimumDistance)
            .onEnded { value in
                let h = value.translation.width, v = value.translation.height
                if abs(h) > abs(v) {
                    onSwipe(h > 0 ? .right : .left)
                } else {
                    onSwipe(v > 0 ? .down : .up)
                }
            }
    }
}

// Usage
Rectangle().gesture(SwipeGesture { print("Swiped \($0)") })

Wrap in a View extension for ergonomic API:

extension View {
    func onSwipe(perform action: @escaping (SwipeGesture.Direction) -> Void) -> some View {
        gesture(SwipeGesture(onSwipe: action))
    }
}

Common Mistakes

1. Conflicting parent/child gestures

// DON'T: Parent .gesture() conflicts with child tap
VStack {
    Button("Action") { doSomething() }
}
.gesture(TapGesture().onEnded { parentAction() })

// DO: Use .simultaneousGesture() or .highPriorityGesture()
VStack {
    Button("Action") { doSomething() }
}
.simultaneousGesture(TapGesture().onEnded { parentAction() })

2. Using @State instead of @GestureState for transient state

// DON'T: @State doesn't auto-reset — view stays offset after gesture ends
@State private var dragOffset = CGSize.zero

DragGesture()
    .onChanged { value in dragOffset = value.translation }
    .onEnded { _ in dragOffset = .zero }  // manual reset required

// DO: @GestureState auto-resets when gesture ends
@GestureState private var dragOffset = CGSize.zero

DragGesture()
    .updating($dragOffset) { value, state, _ in
        state = value.translation
    }

3. Not using.updating() for intermediate feedback

// DON'T: No visual feedback during long press
LongPressGesture(minimumDuration: 2.0)
    .onEnded { _ in showResult = true }

// DO: Provide feedback while pressing
@GestureState private var isPressing = false

LongPressGesture(minimumDuration: 2.0)
    .updating($isPressing) { current, state, _ in
        state = current
    }
    .onEnded { _ in showResult = true }

4. Using deprecated gesture types on iOS 17+

// DON'T: Deprecated since iOS 17
MagnificationGesture()   // deprecated — use MagnifyGesture()

// DO: Use newer gesture types
MagnifyGesture()         // iOS 17+
RotateGesture()          // iOS 17+ (newer alternative to RotationGesture)

5. Heavy computation in onChanged

// DON'T: Expensive work called every frame (~60-120 Hz)
DragGesture()
    .onChanged { value in
        let result = performExpensiveHitTest(at: value.location)
        let filtered = applyComplexFilter(result)
        updateModel(filtered)
    }

// DO: Throttle or defer expensive work
DragGesture()
    .onChanged { value in
        dragPosition = value.location  // lightweight state update only
    }
    .onEnded { value in
        performExpensiveHitTest(at: value.location)  // once at end
    }

6. Using onTapGesture for actions that should be a Button

// DON'T: onTapGesture has no accessibility traits, VoiceOver role,
// Voice Control targeting, Switch Control scanning, or keyboard activation
Text("Delete")
    .onTapGesture { deleteItem() }

// DO: Button provides all of these automatically
Button("Delete", role: .destructive) { deleteItem() }

// DO: For custom visuals, use ButtonStyle instead of onTapGesture
Button { toggleExpanded() } label: {
    CardView()
}
.buttonStyle(.plain)

Reserve onTapGesture for multi-tap (count: 2+), tap-location-dependent behavior, or adding tap recognition to non-interactive content that already has appropriate accessibility traits.

Review Checklist

• Correct gesture type: MagnifyGesture/RotateGesture (not deprecated Magnification/Rotation variants)
• @GestureState used for transient values that should reset; @State for persisted values
• .updating() provides intermediate visual feedback during continuous gestures
• Parent/child conflicts resolved with .highPriorityGesture() or .simultaneousGesture()
• onChanged closures are lightweight — no heavy computation every frame
• Composed gestures use correct combinator: simultaneously, sequenced, or exclusively
• Persisted scale/rotation clamped to reasonable bounds in onEnded
• Custom Gesture conformances use var body: some Gesture (not View)
• Gesture-driven animations use .spring or similar for natural deceleration
• GestureMask considered when mixing gestures across view hierarchy levels
• onTapGesture only used where count > 1, tap location, or coordinate space matters — plain single-tap actions use Button instead

References

• See references/gesture-patterns.md for drag-to-reorder, pinch-to-zoom, combined rotate+scale, velocity calculations, and SwiftUI/UIKit gesture interop.
• Gesture protocol
• TapGesture
• LongPressGesture
• DragGesture
• MagnifyGesture
• RotateGesture
• GestureState
• Composing SwiftUI gestures
• Adding interactivity with gestures