ViewController.swift

import UIKit
import PencilKit

class ViewController: UIViewController {

    @IBOutlet weak var canvasView: PKCanvasView!

    private let toolPicker = PKToolPicker()

    override func viewDidLoad() {
        super.viewDidLoad()

        canvasView.drawingPolicy = .anyInput
        canvasView.tool = PKInkingTool(.pen, color: .black, width: 30)

        toolPicker.addObserver(canvasView)
        toolPicker.setVisible(true, forFirstResponder: canvasView)
        canvasView.becomeFirstResponder()
    }
}