UIViewControllerAnimatedTransitioning

UIViewControllerAnimatedTransitioning.swift

extension MyViewController: UIViewControllerAnimatedTransitioning {
    func transitionDuration(using transitionContext: UIViewControllerContextTransitioning?) -> TimeInterval {
        return 2.0
    }
    
    func animateTransition(using transitionContext: UIViewControllerContextTransitioning) {
        // Retrieve the view controllers participating in the current transition from the context.
        let fromView = transitionContext.viewController(forKey: .from)!.view!
        let toView = transitionContext.viewController(forKey: .to)!.view!

        // If the view to transition from is this controller's view, the drawer is being presented.
        let isPresentingDrawer = fromView == view
        
        let drawerView = isPresentingDrawer ? toView : fromView

        if isPresentingDrawer {
            // Any presented views must be part of the container view's hierarchy
            transitionContext.containerView.addSubview(drawerView)
        }

        /***** Animation *****/
        
        let drawerSize = CGSize(
            width: UIScreen.main.bounds.size.width * 0.5,
            height: UIScreen.main.bounds.size.height)
        
        // Determine the drawer frame for both on and off screen positions.
        let offScreenDrawerFrame = CGRect(origin: CGPoint(x: drawerSize.width * -1, y:0), size: drawerSize)
        let onScreenDrawerFrame = CGRect(origin: .zero, size: drawerSize)
        
        drawerView.frame = isPresentingDrawer ? offScreenDrawerFrame : onScreenDrawerFrame
        
        let animationDuration = transitionDuration(using: transitionContext)
        
        // Animate the drawer sliding in and out.
        UIView.animate(withDuration: animationDuration, animations: {
            drawerView.frame = isPresentingDrawer ? onScreenDrawerFrame : offScreenDrawerFrame
        }, completion: { (success) in
            // Cleanup view hierarchy
            if !isPresentingDrawer {
                drawerView.removeFromSuperview()
            }
            
            // IMPORTANT: Notify UIKit that the transition is complete.
            transitionContext.completeTransition(success)
        })
    }
}