How to properly copy CAShapeLayer in swift?

Question

I'm trying to create copies of CAShapeLayer in swift but I'm getting a crash

Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[CAShapeLayer copyWithZone:]: unrecognized selector sent to instance 0x282e87e60'

which extra steps should I take to allow CALayer .copy() work without crashing the app? Even if I don't cast the result of .copy() it stills fails exactly at that copy() line...

private var drawLines: [CAShapeLayer]
func getCopiedLayers() -> [CAShapeLayer] {
    return drawLines.compactMap { layer -> CAShapeLayer? in
        return layer.copy() as? CAShapeLayer
    }
}

what I'm doing wrong here? Thanks in advance for the answers

because CAShapeLayer are reference types and I don't want the future modifications I'm going to perform on the layers affect the original layers — Lucas, Jan 11 '20 at 13:50

score 2 · Accepted Answer · edited Aug 23 '22 at 14:41

CALayer does not conform to NSCopying from API, but it conforms to NSSecureCoding, so it is possible to add copying capability as below

Tested with Xcode 11.2 / iOS 13.2 (with CAShapeLayer & CAGradientLayer)

extension CALayer : NSCopying {
    public func copy(with zone: NSZone? = nil) -> Any {
        if let data = try? NSKeyedArchiver.archivedData(withRootObject: self, requiringSecureCoding: false) {
            if let newInstance = try? NSKeyedUnarchiver.unarchiveTopLevelObjectWithData(data) {
                return newInstance
            }
        }
        fatalError() // << should never got here
    }
}

Now, it is possible to call layer.copy() to any layer (theoretically) without exception.

How to properly copy CAShapeLayer in swift?

1 Answers1