Gesture recognizer with delaysTouchesBegan stops all calls to touchesMoved?

Question

The view controller code below demonstrates my question. It prints some debugging statements in response to touch events and a pinch gesture.

If the gesture recognizer is disabled, and I drag a finger on the screen, everything works as I expected: the controller gets a touchesBegan, a bunch of touchesMoved, and a touchesEnded. But if I enable the gesture recognizer and set its delaysTouchesBegan property to true, and drag a single finger, the controller receives only touchesBegan and touchesEnded calls - no touchesMoved.

The docs for delaysTouchesBegan suggest that touch events will pile up and be delivered after the gesture recognizer fails. Is this the expected behavior - to lose all the touchesMoved events?

class ViewController: UIViewController {

    var gr: UIPinchGestureRecognizer!

    override func viewDidLoad() {
        super.viewDidLoad()
        gr = UIPinchGestureRecognizer(target: self, action: #selector(pinched(_:)))
        gr.delaysTouchesBegan = true
        view.addGestureRecognizer(gr)
    }

    @IBAction func buttonTapped(_ sender: Any) {
        gr.isEnabled = !gr.isEnabled
        print("pinch recognizer enabled: \(gr.isEnabled)")
    }

    @objc func pinched(_ gr: Any?) {
        print("pinched")
    }

    var i = 0

    override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
        i = 0
        print("touchesBegan")
    }

    override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent?) {
        print("touchesMoved \(i)")
        i += 1
    }

    override func touchesEnded(_ touches: Set<UITouch>, with event: UIEvent?) {
        print("touchesEnded")
    }

    override func touchesCancelled(_ touches: Set<UITouch>, with event: UIEvent?) {
        print("touchesCancelled")
    }
}

Caleb Wells Caleb Wells · Accepted Answer · 2018-04-13T18:52:44

A pinch gesture recognizer reports changes each time the distance between the fingers change. The distance between the fingers is reported as a scale factor. So you will want to look at the scale factor, not touchesMoved. Was that helpful?

@objc func pinched(_ gr: UIPinchGestureRecognizer) {

    if gr.state == .began  {
        print("began")
    }

    if gr.state == .changed {
        print("scale: \(gr.scale)")
    }

    if gr.state == .ended {
        print("ended")
    }
}

Handling Pinch Gestures

Handling Pinch Gestures ( Swift 4 - 2018 )

Gesture recognizer with delaysTouchesBegan stops all calls to touchesMoved?

1 Answers