How to Get the Coordinates of a Touch Gesture on a PKCanvasView using PencilKit? Swift 5 & Xcode 11

Question

NOTE that I looked a lot everywhere but couldn't find a solution.

Using the Storyboard, I have a ViewController, with a View (UIView) and a Subview (PKCanvasView) where I want to use PencilKit to draw on the latter.

_

My objectives are:

1. Draw only on this PKCanvasView

2. Get the coordinates in real time of where I'm drawing on the PKCanvasView

My results:

1. I can draw on the PKCanvasView only if I start from this view, and I can only draw within the frame of this PKCanvasView. That's good.

2. I can only manage to get the coordinates of where I'm touching the screen IF I start the gesture on the UIView. BUT Not if I touch the PKCanvasView first.

My problem:

How do I get the coordinates of where I'm drawing on the PKCanvasView?

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Below is my code:

import UIKit
import PencilKit

class ViewController: UIViewController {

    @IBOutlet weak var labelText: UILabel! //Label object to display the coordinates

    @IBOutlet weak var canvasView: PKCanvasView! //Subview to draw on

    override func viewDidAppear(_ animated: Bool) {
        canvasView.tool = PKInkingTool(.pen, color: .black, width: 10)
    }

    // MARK: FUNCTIONS //
    override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
        touches.forEach { (touch) in
            updateGagues(with: touch)
        }
    }

    override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent?) {
        touches.forEach { (touch) in
            updateGagues(with: touch)
        }
    }

    private func updateGagues(with touch: UITouch) {
        let location = touch.preciseLocation(in: view)
        labelText.text = location.debugDescription
    }
}

Answer 1

I recently experienced the same problem of getting touch coordinates from my PKCanvasView. To do this, I created a subclass of PKCanvasView and overrode the touchesBegan function:

class Canvas: PKCanvasView {

  override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
    touches.forEach { touch in
      print("touch location \(touch.location(in: self))")
    }
  }

}