listening for multitouch events in OS X using the touchesBegan and touchesMoved event handlers

Question

I am trying to record touches and finger movements that users perform on a 2018 MacBook Trackpad.

When I try to test the API and print to console when the user touches the Trackpad, I see no output.

How do I listen for touch events and get data from them?

I referred to the handling Trackpad events documentation. The handling multitouch events section of the page says:

A view by default does not accept touch events. To handle touch events, your custom view must first call the NSView method setAcceptsTouchEvents: with an argument of YES.

However, the setAcceptsTouchEvents documentation says the method is deprecated.

When I try just printing a log on detecting a touch to test if the API is working, I do not see any console output. here is my code:

import Cocoa

class ViewController: NSViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view.
    }

    override var representedObject: Any? {
        didSet {
        // Update the view, if already loaded.
        }
    }

    override func touchesBegan(with event: NSEvent) {
        print("touched!");
    }

}

how do I get the console statement to print something?

Answer 1

I was playing around with this and here is what I figured out.

override func viewDidLoad() {
    super.viewDidLoad()

    // Do any additional setup after loading the //view.
    //view.acceptsTouchEvents = true; //deprecated but works.deprecated
    view.allowedTouchTypes = [NSTouch.TouchTypeMask.direct, NSTouch.TouchTypeMask.indirect];
}

and then, you can override the functions when touches are in different phases as explained in the question.

Answer 2

Note that to do the "allowedTouchTypes" massage in a subclass it is like this:

import Cocoa

class UnView: NSView{
    override var allowedTouchTypes: NSTouch.TouchTypeMask {
        get { return [] } .. as you wish
        set { }
    }
    
}