SpringWithDamping for CALayer animations?

Question

After playing around a lot with the UIView dynamic animations introduced in iOS 7, most notably:

[UIView animateWithDuration: delay: usingSpringWithDamping: initialSpringVelocity: options: animations: completion:];

I was wondering if there is an equivalent to 'SpringWithDamping/Velocity' method that can be accessed directly when creating a CALayer animation? I.e. either through CATransaction, CABasicAnimation or otherwise...

Thanks

Answer 1

There is (and have been for a while) a private class called CASpringAnimation that I'm pretty sure is being used behind it all (but I haven't verified it). Unfortunately, it is still private.

Answer 2

in iOS9 Apple finally made the CASpringAnimation class public.

You can use it like that:

let spring = CASpringAnimation(keyPath: "position.x")
spring.damping = 5
spring.fromValue = myLayer.position.x
spring.toValue = myLayer.position.x + 100.0
spring.duration = spring.settlingDuration
myLayer.addAnimation(spring, forKey: nil)

Notice that you cannot set the animation duration - you need to ask the CASpringAnimation class for the settlingDuration (e.g. "How much time is going to take for the spring system to settle down") and then set it as the duration of your animation.

Check the header files for CASpringAnimation - it exposes a number of spring system variables you can adjust - stiffness, mass, etc.

Answer 3

As David said, CASpringAnimation is private (for now?), but I recently came across RBBSpringAnimation from the RBBAnimation project.

I can definitely recommend this, it was very easy to drop in as a replacement for my existing CABasicAnimation.

Answer 4

I wrote a class to create CASpringAnimation instance. It works in a pretty simple way:

By creating a spring animation from UIKit API, it arrests the created CASpringAnimation instance from the view's layer, copies it and returns it.

But I don't know if it is App Store safe that to create CASpringAnimation in this way.

import UIKit

private let SharedCASpringAnimationFactory = CASpringAnimationFactory()

public class CASpringAnimationFactory {
    private var dummyView: UIView

    private init() {
        dummyView = UIView(frame: CGRect.zeroRect)
    }

    private class var shared: CASpringAnimationFactory {
        return SharedCASpringAnimationFactory
    }


     public class func animation(#keyPath: String, dumping: CGFloat, initialSpringVelocity: CGFloat) -> CABasicAnimation {
        let duration = CATransaction.animationDuration()

        UIView.animateWithDuration(duration, delay: 0.0, usingSpringWithDamping: dumping, initialSpringVelocity: initialSpringVelocity, options: nil,
            animations: { () -> Void in
                CASpringAnimationFactory.shared.dummyView.bounds = CGRect(origin: CGPoint.zero, size: CGSize(width: 100, height: 100))
            }, completion: nil)

        let dummyLayer = CASpringAnimationFactory.shared.dummyView.layer

        let animations = dummyLayer.animationKeys().map {dummyLayer.animationForKey($0 as String) as CAAnimation}

        let arrestedAnimation = animations.first!.copy() as CABasicAnimation
        arrestedAnimation.keyPath = keyPath
        arrestedAnimation.fromValue = nil
        arrestedAnimation.toValue = nil

        dummyLayer.removeAllAnimations()
        shared.dummyView.bounds = CGRect.zeroRect

        return arrestedAnimation
    }
}