UIViewController transitions

ContainerViewController.swift

import UIKit

class ContainerViewController: UIViewController {

    private var childVwCtrl: UIViewController

    var contentViewController: UIViewController {
        get { childVwCtrl }
        set { set(contentViewController: newValue, animationDuration: nil) }
    }

    func set(contentViewController toVwCtrl: UIViewController, animationDuration: Double?) {
        let fromVwCtrl = childVwCtrl

        guard let duration = animationDuration else {
            remove(viewController: fromVwCtrl)
            add(viewController: toVwCtrl)
            childVwCtrl = toVwCtrl
            return
        }

        addChild(toVwCtrl)
        toVwCtrl.view.frame = contentFrame
        fromVwCtrl.willMove(toParent: nil)
        beginAnimation(fromView: fromVwCtrl.view, toView: toVwCtrl.view)
        transition(
            from: fromVwCtrl,
            to: toVwCtrl,
            duration: duration,
            options: [.curveEaseOut],
            animations: {
                self.endAnimation(
                    fromView: fromVwCtrl.view,
                    toView: toVwCtrl.view
                )
            },
            completion: { _ in
                toVwCtrl.didMove(toParent: self)
                fromVwCtrl.removeFromParent()
                self.childVwCtrl = toVwCtrl
            }
        )
    }

    private func beginAnimation(fromView: UIView, toView: UIView) {
        fromView.transform = CGAffineTransform.identity
        toView.transform = CGAffineTransform(translationX: 500, y: 0)
    }

    private func endAnimation(fromView: UIView, toView: UIView) {
        fromView.transform = CGAffineTransform(translationX: -500, y: 0)
        toView.transform = CGAffineTransform.identity
    }

    init(contentViewController: UIViewController) {
        childVwCtrl = contentViewController
        super.init(nibName: nil, bundle: nil)
        add(viewController: contentViewController)
    }

    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    override func viewDidLoad() {
        super.viewDidLoad()
        view.backgroundColor = .lightGray
    }

    private var contentFrame: CGRect {
        let edge = view.bounds.size.minEdge - 100
        return CGRect.sized(edge).offsetBy(dx: 50, dy: 200)
    }

    private var contentEdgeInsets: UIEdgeInsets {
        return UIEdgeInsets.from(outer: view.bounds, inner: contentFrame)
    }

    private func add(viewController: UIViewController) {
        addChild(viewController)
        view.addSubview(viewController.view)
        viewController.view.frame = contentFrame
        viewController.didMove(toParent: self)
    }

    private func remove(viewController: UIViewController) {
        viewController.willMove(toParent: nil)
        viewController.view.removeFromSuperview()
        viewController.removeFromParent()
    }
}

SomeViewController.swift

import UIKit

class SomeViewController: UIViewController {
    let desc: String

    init(desc: String) {
        self.desc = desc
        super.init(nibName: nil, bundle: nil)
    }

    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    override func viewDidLoad() {
        super.viewDidLoad()
        view.backgroundColor = UIColor(hue: CGFloat.random(in: 0...1),
                                       saturation: 0.8,
                                       brightness: 0.8,
                                       alpha: 1)
        let label = UILabel(frame: CGRect(origin: .zero, size: CGSize(width: 100, height: 80)))
        view.addSubview(label)
        view.addConstraints(to: label)
        label.text = desc
        label.font = UIFont.systemFont(ofSize: 24, weight: .bold)
        label.textAlignment = .center
    }

    override var description: String {
        return desc
    }
}

UIKit+Helpers.swift

import UIKit

extension CGSize {
    var minEdge: CGFloat { min(width, height) }
    func offset(_ val: CGFloat) -> CGSize {
        return CGSize(width: width - val, height: height - val)
    }
}

extension CGRect {
    static func sized(_ value: CGFloat) -> CGRect {
        return CGRect(origin: .zero, size: CGSize(width: value, height: value))
    }
}

extension UIEdgeInsets {
    static func from(outer: CGRect, inner: CGRect) -> UIEdgeInsets {
        return UIEdgeInsets(
            top: inner.minY - outer.minY,
            left: inner.minX - outer.minX,
            bottom: outer.maxY - inner.maxY,
            right: outer.maxX - inner.maxX)
    }
    static func all(_ value: CGFloat) -> UIEdgeInsets {
        return UIEdgeInsets(top: value, left: value, bottom: value, right: value)
    }
}

extension UIView {
    func addConstraints(to subview: UIView, insets: UIEdgeInsets = .zero) {
        subview.translatesAutoresizingMaskIntoConstraints = false
        NSLayoutConstraint.activate(NSLayoutConstraint.constraints(
            withVisualFormat: "V:|-(\(insets.top))-[vw]-(\(insets.bottom))-|",
            metrics: nil,
            views: ["vw": subview]
        ))
        NSLayoutConstraint.activate(NSLayoutConstraint.constraints(
            withVisualFormat: "H:|-(\(insets.left))-[vw]-(\(insets.right))-|",
            metrics: nil,
            views: ["vw": subview]
        ))
    }
}

ViewController.swift

class ViewController: UIViewController {
    var containerVwCtrl: ContainerViewController!
    var vwCtrls: [SomeViewController] = []
    var selectedIndex = 0
    var timer: Timer!

    override func viewDidLoad() {
        super.viewDidLoad()
        vwCtrls = (0..<5).map { SomeViewController(desc: "Child \($0)") }
        containerVwCtrl = ContainerViewController(contentViewController: vwCtrls[selectedIndex])
        containerVwCtrl.modalPresentationStyle = .fullScreen
    }

    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)
        present(containerVwCtrl, animated: false)
        timer = Timer.scheduledTimer(
            timeInterval: 3,
            target: self, selector: #selector(displayNext),
            userInfo: nil, repeats: true)
    }

    @objc func displayNext() {
        selectedIndex = (selectedIndex + 1) % vwCtrls.count
        containerVwCtrl.set(contentViewController: vwCtrls[selectedIndex], animationDuration: 1)
    }
}