swift - 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

You can use the .updating modifier like this:

struct TapTestView: View {

    @GestureState private var isTapped = false

    var body: some View {

        let tap = DragGesture(minimumDistance: 0)
            .updating($isTapped) { (_, isTapped, _) in
                isTapped = true
            }

        return Text("Tap me!")
            .foregroundColor(isTapped ? .red: .black)
            .gesture(tap)
    }
}

Some notes:

• The zero minimum distance makes sure the gesture is immediately recognised
• The @GestureState property wrapper automatically resets its value to the original value when the gesture ends. This way you only have to worry about setting isTapped to true. It will automatically be false again when the interaction ends.
• The updating modifier has this weird closure with three parameters. In this case we are only interested in the middle one. It's an inout parameter to the wrapped value of the GestureState, so we can set it here. The first parameter has the current value of the gesture; the third one is a Transaction containing some animation context.