这是向 SwiftUI 视图添加捏合缩放的一种方法。它将UIView 与UIPinchGestureRecognizer 覆盖在UIViewRepresentable 中，并通过绑定将相关值转发回SwiftUI。
您可以像这样添加行为：
Image("Zoom")
.pinchToZoom()
这增加了类似于在 Instagram 供稿中缩放照片的行为。完整代码如下：
import UIKit
import SwiftUI
class PinchZoomView: UIView {
weak var delegate: PinchZoomViewDelgate?
private(set) var scale: CGFloat = 0 {
didSet {
delegate?.pinchZoomView(self, didChangeScale: scale)
}
}
private(set) var anchor: UnitPoint = .center {
didSet {
delegate?.pinchZoomView(self, didChangeAnchor: anchor)
}
}
private(set) var offset: CGSize = .zero {
didSet {
delegate?.pinchZoomView(self, didChangeOffset: offset)
}
}
private(set) var isPinching: Bool = false {
didSet {
delegate?.pinchZoomView(self, didChangePinching: isPinching)
}
}
private var startLocation: CGPoint = .zero
private var location: CGPoint = .zero
private var numberOfTouches: Int = 0
init() {
super.init(frame: .zero)
let pinchGesture = UIPinchGestureRecognizer(target: self, action: #selector(pinch(gesture:)))
pinchGesture.cancelsTouchesInView = false
addGestureRecognizer(pinchGesture)
}
required init?(coder: NSCoder) {
fatalError()
}
@objc private func pinch(gesture: UIPinchGestureRecognizer) {
switch gesture.state {
case .began:
isPinching = true
startLocation = gesture.location(in: self)
anchor = UnitPoint(x: startLocation.x / bounds.width, y: startLocation.y / bounds.height)
numberOfTouches = gesture.numberOfTouches
case .changed:
if gesture.numberOfTouches != numberOfTouches {
// If the number of fingers being used changes, the start location needs to be adjusted to avoid jumping.
let newLocation = gesture.location(in: self)
let jumpDifference = CGSize(width: newLocation.x - location.x, height: newLocation.y - location.y)
startLocation = CGPoint(x: startLocation.x + jumpDifference.width, y: startLocation.y + jumpDifference.height)
numberOfTouches = gesture.numberOfTouches
}
scale = gesture.scale
location = gesture.location(in: self)
offset = CGSize(width: location.x - startLocation.x, height: location.y - startLocation.y)
case .ended, .cancelled, .failed:
isPinching = false
scale = 1.0
anchor = .center
offset = .zero
default:
break
}
}
}
protocol PinchZoomViewDelgate: AnyObject {
func pinchZoomView(_ pinchZoomView: PinchZoomView, didChangePinching isPinching: Bool)
func pinchZoomView(_ pinchZoomView: PinchZoomView, didChangeScale scale: CGFloat)
func pinchZoomView(_ pinchZoomView: PinchZoomView, didChangeAnchor anchor: UnitPoint)
func pinchZoomView(_ pinchZoomView: PinchZoomView, didChangeOffset offset: CGSize)
}
struct PinchZoom: UIViewRepresentable {
@Binding var scale: CGFloat
@Binding var anchor: UnitPoint
@Binding var offset: CGSize
@Binding var isPinching: Bool
func makeCoordinator() -> Coordinator {
Coordinator(self)
}
func makeUIView(context: Context) -> PinchZoomView {
let pinchZoomView = PinchZoomView()
pinchZoomView.delegate = context.coordinator
return pinchZoomView
}
func updateUIView(_ pageControl: PinchZoomView, context: Context) { }
class Coordinator: NSObject, PinchZoomViewDelgate {
var pinchZoom: PinchZoom
init(_ pinchZoom: PinchZoom) {
self.pinchZoom = pinchZoom
}
func pinchZoomView(_ pinchZoomView: PinchZoomView, didChangePinching isPinching: Bool) {
pinchZoom.isPinching = isPinching
}
func pinchZoomView(_ pinchZoomView: PinchZoomView, didChangeScale scale: CGFloat) {
pinchZoom.scale = scale
}
func pinchZoomView(_ pinchZoomView: PinchZoomView, didChangeAnchor anchor: UnitPoint) {
pinchZoom.anchor = anchor
}
func pinchZoomView(_ pinchZoomView: PinchZoomView, didChangeOffset offset: CGSize) {
pinchZoom.offset = offset
}
}
}
struct PinchToZoom: ViewModifier {
@State var scale: CGFloat = 1.0
@State var anchor: UnitPoint = .center
@State var offset: CGSize = .zero
@State var isPinching: Bool = false
func body(content: Content) -> some View {
content
.scaleEffect(scale, anchor: anchor)
.offset(offset)
.animation(isPinching ? .none : .spring())
.overlay(PinchZoom(scale: $scale, anchor: $anchor, offset: $offset, isPinching: $isPinching))
}
}
extension View {
func pinchToZoom() -> some View {
self.modifier(PinchToZoom())
}
}