swiftui-gestures

What this skill does

# 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](#gesture-overview)
- [TapGesture](#tapgesture)
- [LongPressGesture](#longpressgesture)
- [DragGesture](#draggesture)
- [MagnifyGesture (iOS 17+)](#magnifygesture-ios-17)
- [RotateGesture (iOS 17+)](#rotategesture-ios-17)
- [Gesture Composition](#gesture-composition)
- [`@GestureState`](#gesturestate)
- [Adding Gestures to Views](#adding-gestures-to-views)
- [Custom Gesture Protocol](#custom-gesture-protocol)
- [Common Mistakes](#common-mistakes)
- [Review Checklist](#review-checklist)
- [References](#references)

## Gesture Overview

| Gesture | Type | Value | Since |
|---|---|---|---|
| `TapGesture` | Discrete | `Void` | iOS 13 |
| `LongPressGesture` | Discrete | `Bool` | iOS 13 |
| `DragGesture` | Continuous | `DragGesture.Value` | iOS 13 |
| `MagnifyGesture` | Continuous | `MagnifyGesture.Value` | iOS 17 |
| `RotateGesture` | Continuous | `RotateGesture.Value` | iOS 17 |
| `SpatialTapGesture` | Discrete | `SpatialTapGesture.Value` | iOS 16 |

**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.

```swift
// 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`.

```swift
// 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()`:

```swift
@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`.

```swift
@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:

```swift
DragGesture(minimumDistance: 20, coordinateSpace: .global)
```

## MagnifyGesture (iOS 17+)

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

```swift
@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:

```swift
@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.

```swift
@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:

```swift
@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

```swift
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

```swift
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)

```swift
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.

```swift
@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:

| Modifier | Behavior |
|---|---|
| `.gesture()` | Default priority. Child gestures win over parent. |
| `.highPriorityGesture()` | Parent gesture takes precedence over child. |
| `.simultaneousGesture()` | Both parent and child gestures fire. |

```swift
// 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:)`:

```swift
.gesture(drag, includin