CrossDesolveSlideSwiftUITab.swift

import SwiftUI
import Introspect

@main
struct DemoApp: App {
    let tabBarControllerDelegate = TabBarControllerDelegate()
    var body: some Scene {
        WindowGroup {
            TabView {
                NavigationView {
                    List {
                        Text("Menu list item 1")
                        Text("Menu list item 2")
                        Text("Menu list item 3")
                        Text("Menu list item 4")
                        Text("Menu list item 5")
                    }.navigationBarTitle("Menu")
                }
                .tabItem {
                    Label("Menu", systemImage: "list.dash")
                }
                
                NavigationView {
                  List{
                    Text("Order list item 1")
                    Text("Order list item 2")
                    Text("Order list item 3")
                    Text("Order list item 4")
                    Text("Order list item 5")
                  }.navigationBarTitle("Order")
                }
                 .tabItem {
                            Label("Order", systemImage: "square.and.pencil")
                        }
            }.introspectTabBarController { (tabBarController) in
                tabBarController.delegate = tabBarControllerDelegate
            }
        }
    }
}


class TabBarTransitionHandler: NSObject, UIViewControllerAnimatedTransitioning {
    
    let viewControllers: [UIViewController]?
    let transitionDuration: Double = 0.35

    init(viewControllers: [UIViewController]?) {
        self.viewControllers = viewControllers
    }

    func transitionDuration(using transitionContext: UIViewControllerContextTransitioning?) -> TimeInterval {
        return TimeInterval(transitionDuration)
    }

    func animateTransition(using transitionContext: UIViewControllerContextTransitioning) {

        guard
            let fromVC = transitionContext.viewController(forKey: UITransitionContextViewControllerKey.from),
            let fromView = fromVC.view,
            let fromIndex = self.viewControllers?.firstIndex(of: fromVC),
            let toVC = transitionContext.viewController(forKey: UITransitionContextViewControllerKey.to),
            let toView = toVC.view,
            let toIndex = self.viewControllers?.firstIndex(of: toVC)
            else {
                transitionContext.completeTransition(false)
                return
        }

        let frame = transitionContext.initialFrame(for: fromVC)
        var fromFrameEnd = frame
        var toFrameStart = frame
        let quarterFrame = frame.width * 0.25 //only animating from 25% of screen width.. can increase to 100% to get complete slide
        fromFrameEnd.origin.x = toIndex > fromIndex ? frame.origin.x - quarterFrame : frame.origin.x + quarterFrame
        toFrameStart.origin.x = toIndex > fromIndex ? frame.origin.x + quarterFrame : frame.origin.x - quarterFrame
        toView.frame = toFrameStart

        let toCoverView = fromView.snapshotView(afterScreenUpdates: false)
        if let toCoverView = toCoverView {
            toView.addSubview(toCoverView)
        }
        let fromCoverView = toView.snapshotView(afterScreenUpdates: false)
        if let fromCoverView = fromCoverView {
            fromView.addSubview(fromCoverView)
        }

        DispatchQueue.main.async {
            transitionContext.containerView.addSubview(toView)
            UIView.animate(withDuration: self.transitionDuration, delay: 0, usingSpringWithDamping: 0.9, initialSpringVelocity: 0.8, options: [.curveEaseOut], animations: {
                fromView.frame = fromFrameEnd
                toView.frame = frame
                toCoverView?.alpha = 0
                fromCoverView?.alpha = 1
            }) { (success) in
                fromCoverView?.removeFromSuperview()
                toCoverView?.removeFromSuperview()
                fromView.removeFromSuperview()
                transitionContext.completeTransition(success)
            }
        }
    }

}