childViewController.swift

/* add */
let childController = MyViewController()
addChildViewController(childController)
childController.view.frame = view.frame  // or any other frame
view.addSubview(childController.view)
childController.didMoveToParentViewController(self)

/* remove */
if let childController = childViewControllers.last {
  childController.willMoveToParentViewController(nil)
  childController.view.removeFromSuperview()
  childController.removeFromParentViewController()
}


/* faster way */
extension UIViewController {
    func configureChildViewController(childController: UIViewController, onView: UIView?) {
        let holderView: UIView = onView ?? self.view
        addChildViewController(childController)
        holderView.addSubview(childController.view)
        constrainViewEqual(holderView, view: childController.view)
        childController.didMoveToParentViewController(self)
    }
    
    func constrainViewEqual(holderView: UIView, view: UIView) {
        view.translatesAutoresizingMaskIntoConstraints = false
        //pin 100 points from the top of the super
        let pinTop = NSLayoutConstraint(item: view, attribute: .Top, relatedBy: .Equal,
                                        toItem: holderView, attribute: .Top, multiplier: 1.0, constant: 0)
        let pinBottom = NSLayoutConstraint(item: view, attribute: .Bottom, relatedBy: .Equal,
                                           toItem: holderView, attribute: .Bottom, multiplier: 1.0, constant: 0)
        let pinLeft = NSLayoutConstraint(item: view, attribute: .Left, relatedBy: .Equal,
                                         toItem: holderView, attribute: .Left, multiplier: 1.0, constant: 0)
        let pinRight = NSLayoutConstraint(item: view, attribute: .Right, relatedBy: .Equal,
                                          toItem: holderView, attribute: .Right, multiplier: 1.0, constant: 0)
        
        holderView.addConstraints([pinTop, pinBottom, pinLeft, pinRight])
    }
}