How do you detect a SwiftUI touchDown event with no movement or duration?

Question

I'm trying to detect when a finger first makes contact with a view in SwiftUI. I could do this very easily with UIKit Events but can't figure this out in SwiftUI.

I've tried a DragGesture with minimum movement of 0 but it still won't change until your finger moves.

TapGesture will only work when you lift your finger and LongPressGesture will not trigger fast enough no matter what I set the parameters to.

DragGesture(minimumDistance: 0, coordinateSpace: .local).onChanged({ _ in print("down")})

LongPressGesture(minimumDuration: 0.01, maximumDistance: 100).onEnded({_ in print("down")})

I want to detect a touchDown event as soon as a finger makes contact with a view. Apple's default gestures have restrictions to either distance or time.

Update: This is not an issue anymore as Apple has seemed to update how DragGesture works or maybe I was experiencing a specific contextual bug.

Answer 1

If you combine the code from these two questions:

How to detect a tap gesture location in SwiftUI?

UITapGestureRecognizer - make it work on touch down, not touch up?

You can make something like this:

ZStack {
    Text("Test")
    TapView {
        print("Tapped")
    }
}

struct TapView: UIViewRepresentable {
    var tappedCallback: (() -> Void)

    func makeUIView(context: UIViewRepresentableContext<TapView>) -> TapView.UIViewType {
        let v = UIView(frame: .zero)
        let gesture = SingleTouchDownGestureRecognizer(target: context.coordinator,
                                                       action: #selector(Coordinator.tapped))
        v.addGestureRecognizer(gesture)
        return v
    }

    class Coordinator: NSObject {
        var tappedCallback: (() -> Void)

        init(tappedCallback: @escaping (() -> Void)) {
            self.tappedCallback = tappedCallback
        }

        @objc func tapped(gesture:UITapGestureRecognizer) {
            self.tappedCallback()
        }
    }

    func makeCoordinator() -> TapView.Coordinator {
        return Coordinator(tappedCallback:self.tappedCallback)
    }

    func updateUIView(_ uiView: UIView,
                      context: UIViewRepresentableContext<TapView>) {
    }
}

class SingleTouchDownGestureRecognizer: UIGestureRecognizer {
    override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent) {
        if self.state == .possible {
            self.state = .recognized
        }
    }
    override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent) {
        self.state = .failed
    }
    override func touchesEnded(_ touches: Set<UITouch>, with event: UIEvent) {
        self.state = .failed
    }
}

There's definitely some abstractions we can make so that the usage is more like the other SwiftUI Gestures, but this is a start. Hopefully Apple builds in support for this at some point.