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

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.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) {
    }
}

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