iOS: Container view - animate push transition when changing child view controllers

Question

Apple discusses how to have a container view controller transition between two child view controllers in this document. I would like to animate a simple push vertical slide up identical to UIModalTransitionStyleCoverVertical in UIModalTransitionStyle. However, transitionFromViewController only allows use of UIViewAnimationOptions, not transition styles. So how would one animate sliding a view up?

It's odd that to transition between child view controllers you can't call a simple push method similar in UINavigationController to animate the transition.

Answer 1

Load child view, set frame with origin.y under bottom screen. After change it to 0 in animation block. Example:

enum Animation {
    case LeftToRight
    case RightToLeft
}

func animationForLoad(fromvc: UIViewController, tovc: UIViewController, with animation: Animation) {

        self.addChildViewController(tovc)
        self.container.addSubview(tovc.view)
        self.currentVC = tovc

        var endOriginx: CGFloat = 0

        if animation == Animation.LeftToRight {
            tovc.view.frame.origin.x = -self.view.bounds.width
            endOriginx += fromvc.view.frame.width
        } else {
            tovc.view.frame.origin.x = self.view.bounds.width
            endOriginx -= fromvc.view.frame.width
        }

        self.transition(from: fromvc, to: tovc, duration: 0.35, options: UIViewAnimationOptions.beginFromCurrentState, animations: {
            tovc.view.frame = fromvc.view.frame
            fromvc.view.frame.origin.x = endOriginx
            }, completion: { (finish) in
                tovc.didMove(toParentViewController: self)
                fromvc.view.removeFromSuperview()
                fromvc.removeFromParentViewController()               
        })           
    }

Above code is transition between 2 child view with push and pop horizontal animation.