Swift: How to enable pinch-to-zoom for CALayer?

Question

I have been trying to scroll and zoom a CALayer, specifically a CAShapeLayer, of several polygon paths. I added the CALayer to a UIScrollView which has successfully enabled scrolling around the CALayer.

However, pinch to zoom is not working. Several tutorials have implemented zooming a UIImageView with the UIScrollViewDelegate essentially like so:

@IBOutlet var scrollView : UIScrollView!
var imageView = UIImageView()
scrollView.addSubview(imageView)

func viewForZoomingInScrollView(scrollView: UIScrollView) -> UIView? {
    return imageView
}

But CALayer is incompatible with UIView and I have found no information on reconciling the difference.

Is there a similar native way to zoom a CALayer in Swift? Is it something really simple that escaped me? Any help would be appreciated; apologies if I am missing the obvious.

Answer 1

After much digging I found the related documentation from Apple. Turns out pinch-to-zoom is handled automatically on CALayers if they are set up correctly. I adapted the demo code for Swift and came up with this basic structure, which worked for me.

class ViewController: UIViewController, UIScrollViewDelegate {

    @IBOutlet var scrollView : UIScrollView!
    var layerView = UIView()
    var shapeLayer= CAShapeLayer()

    func viewForZoomingInScrollView(scrollView: UIScrollView) -> UIView? {
        return layerView // Specify the layer to scroll, cannot be the UIScrollView used for scrolling
    }
    func scrollViewDidEndZooming(scrollView: UIScrollView, withView view: UIView!, atScale scale: CGFloat) {
        // This was noted as required but no inner code is necessary
    }
    override func viewDidLoad() {
        super.viewDidLoad()
        layerView.layer.addSublayer(shapeLayer) // Attach layer to the canvas view
        scrollView.addSubview(layerView) // Attach the views
        // ... Add layer content, set max and min scaling values as well as layer/view sizes to encompass content
    }
    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
    }
}

I hope this helps someone else!