NEW: Subscribe to Hacking with Swift+ and accelerate your learning! >>

How to make a shape draw itself using strokeEnd

Swift version: 5.2

Paul Hudson    @twostraws   

iOS makes it easy to draw shapes using CAShapeLayer, but you also get the ability to adjust how shapes are drawn. By manipulating the strokeStart and strokeEnd properties you can make shapes draw themselves on the screen: you can present a half-drawn star, or a three-quarters drawn circle, for example.

However, as clever as that is what’s really neat is being able to animate the drawing process. To try it out, first create a CAShapeLayer with a stroke that’s visible, like this one:

let layer = CAShapeLayer()
let bounds = CGRect(x: 50, y: 50, width: 250, height: 250)
layer.path = UIBezierPath(roundedRect: bounds, byRoundingCorners: .allCorners, cornerRadii: CGSize(width: 20, height: 20)).cgPath
layer.strokeColor = UIColor.black.cgColor
layer.fillColor = nil
layer.lineDashPattern = [8, 6]
view.layer.addSublayer(layer)

Now create and add a CABasicAnimation to adjust the strokeEnd property:

let animation = CABasicAnimation(keyPath: "strokeEnd")
animation.fromValue = 0
animation.toValue = 1
animation.duration = 2
animation.autoreverses = true
animation.repeatCount = .infinity
layer.add(animation, forKey: "line")

I made that animate from 0 (not drawn) to 1 (fully drawn) over two seconds, but also made it reverse at the end and repeat infinite times.

Hacking with Swift is sponsored by NSSpain

SPONSORED Announcing NSSpain 2020: Remote Edition! An online, continuous conference for iOS developers. We’ll start on Thursday and finish on Friday, with talks, activities, and lots of fun for 36 hours, non-stop. Sound good? Join us!

Find out more

Sponsor Hacking with Swift and reach the world's largest Swift community!

Available from iOS 3.2

Similar solutions…

About the Swift Knowledge Base

This is part of the Swift Knowledge Base, a free, searchable collection of solutions for common iOS questions.

BUY OUR BOOKS
Buy Pro Swift Buy Swift Design Patterns Buy Testing Swift Buy Hacking with iOS Buy Swift Coding Challenges Buy Swift on Sundays Volume One Buy Server-Side Swift (Vapor Edition) Buy Advanced iOS Volume One Buy Advanced iOS Volume Two Buy Advanced iOS Volume Three Buy Hacking with watchOS Buy Hacking with tvOS Buy Hacking with macOS Buy Dive Into SpriteKit Buy Swift in Sixty Seconds Buy Objective-C for Swift Developers Buy Server-Side Swift (Kitura Edition) Buy Beyond Code

Was this page useful? Let us know!

Average rating: 4.0/5

Link copied to your pasteboard.