How can I tell my app to ignore a specific touch?

Question

My iPad app needs to be able to completely dismiss specific touches i.e. those that come from a finger or stylus and not from, say, the palm of your hand. The view has multi-touch enabled so that I analyse each touch separately.

I can currently differentiate between these touches using the majorRadius attribute but I'm not sure how I might be able to dismiss the larger touches i.e. those greater than my decided threshold.

let touchThreshold : CGFloat = 21.0

override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
    for touch in touches {
        if touch.majorRadius > touchThreshold {
            //dismiss the touch(???)
        } else {
            //draw touch on screen
        }
    }
}

override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent?) {
    for touch in touches {
        if touch.majorRadius > touchThreshold {
            //dismiss the touch(???)
        } else {
            //draw touch on screen
        }
    }
}

Answer 1

If you only want to detect certain types of touches, here's a possible solution:

Option 1

override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
    touches.forEach { touch in
        switch touch.type {
        case .direct, .pencil:
            handleTouch(for: touch.majorRadius)
        case .indirect:
            // don't do anything
            return
        }
    }
}

func handleTouch(for size: CGFloat) {
    switch size {
    case _ where size > touchThreshold:
        print("do something")
    default:
        print("do something else")
    }
}

Option 2

override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
    touches.filter{($0.type == .direct || $0.type == .pencil || $0.type == .stylus) && $0.majorRadius > touchThreshold}.forEach { touch in
        print("do something")
    }
}

You can read more touch types here.