Container view controller helpers

UIViewController.swift

extension UIViewController {

  func attachChildViewController(_ viewController: UIViewController) {
        attachChildViewController(viewController, to: self.view)
    }

    func attachChildViewController(_ viewController: UIViewController, to view: UIView) {
        self.addChildViewController(viewController)
        view.addSubview(viewController.view)
        viewController.didMove(toParentViewController: self)
    }

    func detachChildViewController(viewController: UIViewController) {
        guard viewController.parent == self else {
            return
        }

        viewController.willMove(toParentViewController: nil)
        viewController.removeFromParentViewController()
        viewController.view.removeFromSuperview()
    }
}