Animate a bezier path drawn in drawRect() Swift

Question

I have this shape that i draw in drawRect()

var rectanglePath = UIBezierPath()

override func drawRect(rect: CGRect) {
    rectanglePath = UIBezierPath(rect: self.bounds)
    rectanglePath.fillWithBlendMode(kCGBlendModeMultiply, alpha: 0.7)
    layer.shouldRasterize = true
}

When prepareForEditing function is called, i want to animate the rectanglePath. I tried

  func prepareForEditing(editing:Bool){
        UIView.animateWithDuration(0.5,
            animations: {
              self.rectanglePath = makeNewShape()
            }
       )
  }

Nothing happens. Can you please tell me what's wrong with my code?

Answer 1

To animate CGPath you cannot use UIView.animation methods. I created custom UIView subclass to show you how can you animate CGPaths shape, please refer to the comments and amend it for your requirements:

class MyView: UIView {

let shapeLayer = CAShapeLayer()
let maskLayer = CAShapeLayer()
var rectanglePath = UIBezierPath()

override func didMoveToSuperview() {
    super.didMoveToSuperview()

    backgroundColor = UIColor.clear

    // initial shape of the view
    rectanglePath = UIBezierPath(rect: bounds)

    // Create initial shape of the view
    shapeLayer.path = rectanglePath.cgPath
    shapeLayer.strokeColor = UIColor.black.cgColor
    shapeLayer.fillColor = UIColor.clear.cgColor
    layer.addSublayer(shapeLayer)

    //mask layer
    maskLayer.path = shapeLayer.path
    maskLayer.position =  shapeLayer.position
    layer.mask = maskLayer
}

func prepareForEditing(editing:Bool){

    let animation = CABasicAnimation(keyPath: "path")
    animation.duration = 2

    // Your new shape here
    animation.toValue = UIBezierPath(ovalIn: bounds).cgPath
    animation.timingFunction = CAMediaTimingFunction(name: kCAMediaTimingFunctionEaseOut)

    // The next two line preserves the final shape of animation,
    // if you remove it the shape will return to the original shape after the animation finished
    animation.fillMode = kCAFillModeForwards
    animation.isRemovedOnCompletion = false

    shapeLayer.add(animation, forKey: nil)
    maskLayer.add(animation, forKey: nil)
  }
}