UIViewController.swift

extension UIViewController {
    
    func add(_ child: UIViewController) {
        addChildViewController(child)
        view.addSubview(child.view)
        child.view.frame = view.bounds
        child.view.autoresizingMask = [.flexibleWidth, .flexibleHeight]
        child.didMove(toParentViewController: self)
    }
    
    func remove(_ child: UIViewController) {
        child.willMove(toParentViewController: nil)
        child.view.removeFromSuperview()
        child.removeFromParentViewController()
    }
    
}