UIKitVersusSwiftUIAnimationFrameRate.swift

import UIKit
import SwiftUI

class ViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()
        
        let box = UIView()
        box.frame = CGRect(x: (view.bounds.width / 2.0) - 100.0, y: 0.0, width: 100.0, height: 100.0)
        box.backgroundColor = .systemGreen
        view.addSubview(box)

        // An ever so slight delay is required to sync them up
        UIView.animate(withDuration: 0.5, delay: 0.025, options: [.curveLinear, .repeat, .autoreverse]) {
            box.frame.origin.y = 600.0
        }
        
        let hostingController = UIHostingController(rootView: ContentView())
        
        view.addSubview(hostingController.view)
        hostingController.didMove(toParent: self)
        
        hostingController.view.frame = CGRect(x: view.bounds.width / 2.0, y: 0.0, width: view.bounds.width / 2.0, height: view.bounds.height)
    }
}

struct ContentView: View {
    @State var offsetY = 0.0
    
    var body: some View {
        ZStack(alignment: .topLeading) {
            Color.clear
            
            Rectangle()
                .foregroundColor(.red)
                .frame(width: 100.0, height: 100.0)
                .offset(y: offsetY)
                .onAppear {
                    let animation = Animation.linear(duration: 0.5).repeatForever()

                    withAnimation(animation) {
                        offsetY = 600.0
                    }
                }
        }
        .ignoresSafeArea()
    }
}