AnimationView.swift

import UIKit
import Lottie

/// This class deals with the problems of updating animation frame with Lottie
/// as described here https://github.com/airbnb/lottie-ios/issues/763
class AnimationView: UIView {

    private var previousSize: CGSize?
    private var frameUpdateDisplayLink: CADisplayLink?
    private var animationView: LOTAnimationView! = nil

    required init?(coder aDecoder: NSCoder) {
        super.init(coder:aDecoder)
        commonInit()
    }

    override init(frame: CGRect) {
        super.init(frame: frame)
        commonInit()
    }

    func play(fromProgress: CGFloat = 0.0,
              toProgress: CGFloat = 1.0,
              withCompletion completion:LOTAnimationCompletionBlock? = nil ) {
        animationView.play(fromProgress: fromProgress,
                           toProgress: toProgress,
                           withCompletion: completion)
    }

    override var bounds: CGRect {
        didSet {
            startFrameUpdateLink()
        }
    }

    func setAnimation(named animationName:String) {
        animationView.setAnimation(named: animationName)
    }

    deinit {
        stopFrameUpdateLink()
    }
}

private extension AnimationView {

    func commonInit() {
        animationView = LOTAnimationView(frame: self.bounds)
        addSubview(animationView)
    }

    func startFrameUpdateLink() {
        stopFrameUpdateLink()

        frameUpdateDisplayLink = CADisplayLink(target: self, selector: #selector(update))
        frameUpdateDisplayLink?.add(to: .current, forMode: .common)
    }

    func stopFrameUpdateLink() {
        frameUpdateDisplayLink?.invalidate()
        frameUpdateDisplayLink = nil

        previousSize = nil
    }

    @objc func update() {
        guard let size = self.layer.presentation()?.frame.size else {
            return
        }

        animationView.frame = CGRect(origin: .zero, size: size)

        if size == previousSize {
            stopFrameUpdateLink()
        }

        previousSize = size
    }
}