I have a custom modifier on a SwiftUI View to pan and zoom an Image. I need to get the location where the user long presses. The modifier uses an UIView (UIViewRepresentable) under the hood where the pinch-and-zoom gesture is added to the view. Adding the longPressGesture directly to the modifier (swiftUI View) conflicts with this pinch-and-zoom gesture. Thus I added a longPress gesture directly to the UIView. This works well. However, I need the location (CGPoint) up the chain in my ViewModifier to for a Binding to the calling View. I can't seem to work out how to do that...

SHORT: I need tapLocation on my ViewModifier to have the value of the. long press in the UIView!

Calling View:

let arrowPointUp = Image(systemName: "arrowtriangle.up.fill")

struct ContentView: View {
    @State private var mapImage = UIImage(named: "worldMap")!
    @State private var tapLocation = CGPoint.zero
    @State private var height = 0.0
    @State private var width = 0.0

    var body: some View {
        GeometryReader { proxy in
            ZStack {
                Image(uiImage: mapImage)
                    .resizable()
                    .fixedSize()

                arrowPointUp
                    .foregroundColor(.green)
                    .position(tapLocation)

                arrowPointUp
                    .foregroundColor(.red)
                    .position(x: 776, y: 1150)

                arrowPointUp
                    .foregroundColor(.blue)
                    .position(x: 1178, y: 1317)
            }
            .frame(width: mapImage.size.width, height: mapImage.size.height)
            .PinchToZoomAndPan(contentSize: mapImage.size, tapLocation: $tapLocation)
        }
    }
}

The ViewModifier

import SwiftUI
import UIKit

extension View {
    func PinchToZoomAndPan(contentSize: CGSize, tapLocation: Binding<CGPoint>) -> some View {
        modifier(PinchAndZoomModifier(contentSize: contentSize, tapLocation: tapLocation))
    }
}

struct PinchAndZoomModifier: ViewModifier {
    private var contentSize: CGSize
    private var min: CGFloat = 0.75 // 1.0
    private var max: CGFloat = 3.0
    @State var currentScale: CGFloat = 1.0

    @Binding var tapLocation: CGPoint

    init(contentSize: CGSize, tapLocation: Binding<CGPoint>) {
        self.contentSize = contentSize
        self._tapLocation = tapLocation
        print("ContentSize: \(self.contentSize)")
    }

    var doubleTapGesture: some Gesture {
        TapGesture(count: 2).onEnded {
            currentScale = 1.0
        }
    }

    func body(content: Content) -> some View {
        ScrollView([.horizontal, .vertical]) {
            content
                .frame(width: contentSize.width * currentScale, height: contentSize.height * currentScale, alignment: .center)
                .modifier(PinchToZoom(minScale: min, maxScale: max, scale: $currentScale))
                .simultaneousGesture(doubleTapGesture)
        }
        .animation(.easeInOut, value: currentScale)
    }
}

// THREE
class PinchZoomView: UIView {
    let minScale: CGFloat
    let maxScale: CGFloat
    var isPinching: Bool = false
    var scale: CGFloat = 1.0
    let scaleChange: (CGFloat) -> Void

    var longPressLocation = CGPoint.zero

    init(minScale: CGFloat,
           maxScale: CGFloat,
         currentScale: CGFloat,
         scaleChange: @escaping (CGFloat) -> Void) {
        self.minScale = minScale
        self.maxScale = maxScale
        self.scale = currentScale
        self.scaleChange = scaleChange
        super.init(frame: .zero)
        let pinchGesture = UIPinchGestureRecognizer(target: self, action: #selector(pinch(gesture:)))
        pinchGesture.cancelsTouchesInView = false
        let longPressGesture = UILongPressGestureRecognizer(target: self, action: #selector(longPress(gesture:)))
        addGestureRecognizer(pinchGesture)
        addGestureRecognizer(longPressGesture)
    }

    required init?(coder: NSCoder) {
        fatalError()
    }

    @objc private func longPress(gesture: UILongPressGestureRecognizer) {
        switch gesture.state {
        case .ended:
            longPressLocation = gesture.location(in: self)
            print("Long Pressed in UIView on \(longPressLocation) with scale \(scale)")
        default:
            break
        }
    }

    @objc private func pinch(gesture: UIPinchGestureRecognizer) {
        switch gesture.state {
        case .began:
            isPinching = true

        case .changed, .ended:
            if gesture.scale <= minScale {
                scale = minScale
            } else if gesture.scale >= maxScale {
                scale = maxScale
            } else {
                scale = gesture.scale
            }
            scaleChange(scale)
        case .cancelled, .failed:
            isPinching = false
            scale = 1.0
        default:
            break
        }
    }
}

// TWO
struct PinchZoom: UIViewRepresentable {
    let minScale: CGFloat
    let maxScale: CGFloat
    @Binding var scale: CGFloat
    @Binding var isPinching: Bool

    func makeUIView(context: Context) -> PinchZoomView {
        let pinchZoomView = PinchZoomView(minScale: minScale, maxScale: maxScale, currentScale: scale, scaleChange: { scale = $0 })
        return pinchZoomView
    }

    func updateUIView(_ pageControl: PinchZoomView, context: Context) { }
}

// ONE
struct PinchToZoom: ViewModifier {
    let minScale: CGFloat
    let maxScale: CGFloat
    @Binding var scale: CGFloat
    @State var anchor: UnitPoint = .center
    @State var isPinching: Bool = false

    func body(content: Content) -> some View {
        ZStack {
            content
                .scaleEffect(scale, anchor: anchor)
                .animation(.spring(), value: isPinching)
                .overlay(PinchZoom(minScale: minScale, maxScale: maxScale, scale: $scale, isPinching: $isPinching))
        }
    }
}

GitHub

TIA

I think this video from Nick will give you a hint how you can tackle that challenge. It is not so lengthy but his explanation is just awesome! https://youtu.be/1GYKyQHVDWw

Gonna watch it, hope it helps. Thanks. But wouldn't mind a solution, been at it way to long. ...