I would like a SwiftUI slide transition effect in which the current UIView slides out and next UIView slides in, but the current UIView simply disappears and then the next view slides in, couldn’t find out the reason, I’m using Xcode 14.2 for iOS 16.2.

class SlideTransition: NSObject, UIViewControllerAnimatedTransitioning {
    enum Direction {
        case left, right
    }

    let duration: TimeInterval
    let direction: Direction

    init(duration: TimeInterval = 1, direction: Direction = .left) {
        self.duration = duration
        self.direction = direction
        super.init()
    }

    @objc func transitionDuration(using transitionContext: UIViewControllerContextTransitioning?) -> TimeInterval {
        return duration
    }
    
    @objc func animateTransition(using transitionContext: UIViewControllerContextTransitioning) {
        guard
            let fromView = transitionContext.view(forKey: .from),
            let toView = transitionContext.view(forKey: .to)
        else {
            transitionContext.completeTransition(false)
            return
        }
        
        let containerView = transitionContext.containerView
        let containerBounds = containerView.bounds

        let fromViewEndFrame: CGRect
        let toViewStartFrame: CGRect
        
        // Determine the slide direction
        switch direction {
        case .left:
            fromViewEndFrame = containerBounds.offsetBy(dx: -containerBounds.width, dy: 0)
            toViewStartFrame = containerBounds.offsetBy(dx: containerBounds.width, dy: 0)
        case .right:
            fromViewEndFrame = containerBounds.offsetBy(dx: containerBounds.width, dy: 0)
            toViewStartFrame = containerBounds.offsetBy(dx: -containerBounds.width, dy: 0)
        }

        toView.frame = toViewStartFrame
        
        containerView.addSubview(toView)
        
//        UIView.animate(withDuration: duration, animations: {
//            // Slide out the fromView and slide in the toView
//            fromView.frame = fromViewEndFrame
//            toView.frame = containerBounds
//        }, completion: { finished in
//            let wasCancelled = transitionContext.transitionWasCancelled
//            transitionContext.completeTransition(!wasCancelled)
//            
//            // If the transition was cancelled, remove the toView to avoid a broken state
//            if wasCancelled {
//                toView.removeFromSuperview()
//            }
//        })
        
//        Perform the animation
        let animator = UIViewPropertyAnimator(duration: transitionDuration(using: transitionContext), curve: .easeInOut) {
            // Animate both views simultaneously
            fromView.frame = fromViewEndFrame
            toView.frame = containerBounds
        }

        // Add a completion block to handle the end of the animation
        animator.addCompletion { finished in
            let wasCancelled = transitionContext.transitionWasCancelled
            transitionContext.completeTransition(!wasCancelled)

            // If the transition was canceled, reset the toView's frame to its initial position
            if wasCancelled {
                toView.removeFromSuperview()
            }
        }

        animator.startAnimation()
    }
}

both UIView.animate and UIViewPropertyAnimator have the same results, the current view simply disappears instead of sliding out.

And I tried the HeroTransition library, the transition worked, but unable to set the transition duration.

could someone help? thanks 🙂