How to use Swift 4 KeyPath in CAShapeLayer animation

user_1645068 0
Viewed 2610

If I write Swift 3 code it would look like this:

let animation = CABasicAnimation(keyPath: #keyPath(CAShapeLayer.path))

But I tried to use Swift 4 new syntax for keyPath and I got:

let keyPath = \CAShapeLayer.path
let animation = CABasicAnimation(keyPath: keyPath) // error line

> Error: Cannot convert value of type 'ReferenceWritableKeyPath' to expected argument type 'String?'

How can I use key path in this situation with swift 4?

swift4 swift ios
3 Answers

Yes, it is possible to use swift keypaths. Like:

extension UIView {

func animateLayer<Value>(_ keyPath: WritableKeyPath<CALayer, Value>, to value:Value, duration: CFTimeInterval) {

    let keyString = NSExpression(forKeyPath: keyPath).keyPath
    let animation = CABasicAnimation(keyPath: keyString)
    animation.fromValue = self.layer[keyPath: keyPath]
    animation.toValue = value
    animation.duration = duration
    self.layer.add(animation, forKey: animation.keyPath)
    var thelayer = layer
    thelayer[keyPath: keyPath] = value
}
}

Usage like:

animateLayer(\.shadowOffset, to: CGSize(width: 3, height: 3), duration:1)
animateLayer(\.shadowOpacity, to: 0.4, duration: 1)

It's not thoroughly tested. but worked for me.

user_22575000

For Swift 5 you can use something similar to this:

let ba: CABasicAnimation = CABasicAnimation(keyPath: #keyPath(CAEmitterLayer.emitterPosition))
ba.fromValue = topMid
ba.toValue = topMid.offsetBy(dx: dx, dy: dy)
ba.duration = 6
ba.autoreverses = true
ba.repeatCount = .infinity
snowflakeEmitterLayer.add(ba, forKey: nil)
user_31382380
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