A general hack to prevent Lottie animations from stopping playing after pushing/popping/presenting/dismissing.

LottieFinder.swift

// A general hack to prevent Lottie animations from stopping playing after pushing/popping/presenting/dismissing.
// Usage: LottieFinder.setupLottieFinder()

import UIKit
import Lottie

class LottieFinder {
    static private var operationQueue = OperationQueue()
    static private var operations: [Operation] = []
    static func setupLottieFinder() {
        UIViewController.subscribeLotties()
    }
    
    static func operation(from: UIViewController) {
        operationQueue.cancelAllOperations()
        operations.removeAll()
        let operation = LottieFinderOperation(viewController: from)
        operations.append(contentsOf: [operation])
        operationQueue.addOperation(operation)
    }
}

extension UIViewController {
    
    @objc private dynamic func swizzledLottieViewWillAppear(_ animated: Bool) {
        swizzledLottieViewWillAppear(animated)
        LottieFinder.operation(from: self)
    }
    
    internal static func subscribeLotties() {
        swizzleLottieViewWillAppear()
    }
    
    private static func swizzleLottieViewWillAppear() {
        let selector1 = #selector(UIViewController.viewWillAppear(_:))
        let selector2 = #selector(UIViewController.swizzledLottieViewWillAppear(_:))
        let originalMethod = class_getInstanceMethod(UIViewController.self, selector1)!
        let swizzleMethod = class_getInstanceMethod(UIViewController.self, selector2)!
        method_exchangeImplementations(originalMethod, swizzleMethod)
    }
    
}

class LottieFinderOperation: Operation {
    
    init(viewController: UIViewController) {
        self.viewController = viewController
    }
    
    weak private var viewController: UIViewController?
    
    override func main() {
        guard !isCancelled else { return }
        DispatchQueue.main.async { [weak self] in
            guard let `self` = self, let view = self.viewController?.view else { return }
            for lottie in self.subviews(
                in: view, ofType: AnimationView.self
            ) where lottie.superview != nil {
                guard !self.isCancelled else { break }
                lottie.play()
            }
        }
    }
    
    private func subviews<T: UIView>(in view: UIView, ofType whatType: T.Type) -> [T] {
        var tViews: [T] = []
        for subview in view.subviews {
            guard !isCancelled else { break }
            if let tView = subview as? T {
                tViews.append(tView)
            } else {
                tViews.append(contentsOf: subviews(in: subview, ofType: whatType))
            }
        }
        return isCancelled ? [] : tViews
    }
}