Gesture interfering with sheet drag - swiftui

Question

I am showing a camera preview view on a .sheet.
I need to detect when the user's finger touches the preview area and when the user's finger leaves the preview area.
The only solution I have found to do that was this
CameraPreview()
.gesture(DragGesture(minimumDistance: 0)
.onChanged { _ in
// finger touches
}
.onEnded { _ in
// finger leaves
})
but as this preview is being displayed on a sheet and sheets must be closed by dragging them from the top down, this drag gesture prevents the sheet drag gesture from working.
Any ideas?
NOTE: I do not need to detect dragging. I need to detect single tap on a view and then receive a callback when the finger leaves that view.

Answer 1

You need to use UIViewRepresentable for this. Here are the steps:
Create a custom version of AnyGestureRecognizer taken from here:
class AnyGestureRecognizer: UIGestureRecognizer {
var onCallback: () -> Void
var offCallback: () -> Void
init(target: Any?, onCallback: #escaping () -> Void, offCallback: #escaping () -> Void) {
self.onCallback = onCallback
self.offCallback = offCallback
super.init(target: target, action: nil)
}
override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent) {
if let touchedView = touches.first?.view, touchedView is UIControl {
state = .cancelled
offCallback()
} else if let touchedView = touches.first?.view as? UITextView, touchedView.isEditable {
state = .cancelled
offCallback()
} else {
state = .began
onCallback()
}
}
override func touchesEnded(_ touches: Set<UITouch>, with event: UIEvent?) {
state = .ended
offCallback()
}
override func touchesCancelled(_ touches: Set<UITouch>, with event: UIEvent) {
state = .cancelled
offCallback()
}
}
Create a custom UIViewRepresentable view and attach the AnyGestureRecognizer to it:
struct GestureView: UIViewRepresentable {
var onCallback: () -> Void
var offCallback: () -> Void
func makeUIView(context: UIViewRepresentableContext<GestureView>) -> UIView {
let view = UIView(frame: .zero)
let gesture = AnyGestureRecognizer(
target: context.coordinator,
onCallback: onCallback,
offCallback: offCallback
)
gesture.delegate = context.coordinator
view.addGestureRecognizer(gesture)
return view
}
func updateUIView(_ uiView: UIView, context: UIViewRepresentableContext<GestureView>) {}
class Coordinator: NSObject {}
func makeCoordinator() -> GestureView.Coordinator {
Coordinator()
}
}
extension GestureView.Coordinator: UIGestureRecognizerDelegate {
func gestureRecognizer(_ gestureRecognizer: UIGestureRecognizer, shouldRecognizeSimultaneouslyWith otherGestureRecognizer: UIGestureRecognizer) -> Bool {
true
}
}
Use it as an overlay:
struct ContentView: View {
var body: some View {
Color.blue
.sheet(isPresented: .constant(true)) {
Color.red
.overlay(
GestureView(onCallback: { print("start") }, offCallback: { print("end") })
)
}
}
}