ViewControllerContaining.swift

import Foundation
import UIKit

protocol ViewControllerContaining {
    var containerView: UIView! { get set }
    
    func addViewController(childViewController: UIViewController)
    func removeViewController(childViewController: UIViewController)
    func addChildViewController(childController: UIViewController)
}

extension ViewControllerContaining {
    func addViewController(childViewController: UIViewController) {
        self.addChildViewController(childViewController)
        childViewController.view.frame = containerView.bounds
        containerView.addSubview(childViewController.view)
        childViewController.didMoveToParentViewController(self as? UIViewController)
    }
    
    func removeViewController(childViewController: UIViewController) {
        childViewController.willMoveToParentViewController(nil)
        if childViewController.isViewLoaded() {
            childViewController.view.removeFromSuperview()
        }
        childViewController.removeFromParentViewController()
    }
}