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CS193p class note - 8 Animation

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Memo:
  • The closure you passed to UIViewPropertyAnimator gets executed immediately.
if myView.alpha == 1.0 {
    UIViewPropertyAnimator.runningPropertyAnimator(
        withDuration: 3.0,
               delay: 2.0,
             options: [.allowUserInteraction],
          animations: { view.alpha = 0.0 },
          completion: { if $0 == .end { view.removeFromSuperview() } }
    )
}
// let the views be three times bigger than the original size first
UIViewPropertyAnimator.runningPropertyAnimator(
    withDuration: 0.6,
    delay: 0,
    options: [],
    animations: {
        self.myViews.forEach {
            $0.transform = CGAffineTransform.identity.scaledBy(x: 3.0, y: 3.0)
        }
    },
    completion: { position in
        // do something you hope to achieve after animation is finished
    }
)
  • Dynamic animation: If animating views, all views must be in a view hierarchy with referenceView at the top. There are many dynamic animations, such as collisionBehavior, pushBehavior and so on.
var animator = UIDynamicAnimator(referenceView: UIView)
let gravity = UIGravityBehavior()
animator.addBehavior(gravity)
let item1: UIDynamicItem = ... // usually a UIView
gravity.addItem(item1)
  • we can create a subclass of UIDynamicBehavior and add as many behaviors as we want and override init().
class CardBehavior: UIDynamicBehavior {
    lazy var collisionBehavior: UICollisionBehavior = {
        let behavior = UICollisionBehavior()
        behavior.translatesReferenceBoundsIntoBoundary = true
        return behavior
    }()

    lazy var itemBehavior: UIDynamicItemBehavior = {
        let behavior = UIDynamicItemBehavior()
        behavior.allowsRotation = false
        behavior.elasticity = 1.0
        behavior.resistance = 0
        return behavior
    }()

    private func push(_ item: UIDynamicItem) {
        let push = UIPushBehavior(items: [item], mode: .instantaneous)
        push.angle = ...
        push.magnitude = ...
        push.action = { [unowned push, weak self] in
            self?.removeChildBehavior(push)
        }
        addChildBehavior(push)
    }

    func addItem(_ item: UIDynamicItem) {
        collisionBehavior.addItem(item)
        itemBehavior.addItem(item)
    }

    func removeItem(_ item: UIDynamicItem) {
        collisionBehavior.removeItem(item)
        itemBehavior.removeItem(item)
    }

    override init() {
        super.init()
        addChildBehavior(collisionBehavior)
        addChildBehavior(itemBehavior)
    }

    convenience init(in animator: UIDynamicAnimator) {
        self.init()
        animator.addBehavior(self)
    }
}
  • Add animation using UIView transition
UIView.transition(with: myView,
                  duration: 0.6,
                  options: [.transitionFlipFromLeft],
                  animations: {
    // put the thing you want to animate
})
  • It's perfectly fine to add animation in the completion handler of another animation.

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