Install child view controller

UIViewController+Child.swift

import UIKit

extension UIViewController {
	/// Taken from this great StackOverflow post by Phani Sai: https://stackoverflow.com/a/35473300/78336
	func configureChildViewController(_ childController: UIViewController, onView: UIView?) {
		var holderView = self.view
		if let onView = onView {
			holderView = onView
		}
		addChildViewController(childController)
		holderView?.addSubview(childController.view)
		holderView?.constrainViewEqual(childController.view)
		childController.didMove(toParentViewController: self)
	}
}

extension UIView {
	fileprivate func constrainViewEqual(_ view: UIView) {
		view.translatesAutoresizingMaskIntoConstraints = false
		let pinTop = NSLayoutConstraint(item: view, attribute: .top, relatedBy: .equal,
										toItem: self, attribute: .top, multiplier: 1.0, constant: 0)
		let pinBottom = NSLayoutConstraint(item: view, attribute: .bottom, relatedBy: .equal,
										   toItem: self, attribute: .bottom, multiplier: 1.0, constant: 0)
		let pinLeft = NSLayoutConstraint(item: view, attribute: .left, relatedBy: .equal,
										 toItem: self, attribute: .left, multiplier: 1.0, constant: 0)
		let pinRight = NSLayoutConstraint(item: view, attribute: .right, relatedBy: .equal,
										  toItem: self, attribute: .right, multiplier: 1.0, constant: 0)
		self.addConstraints([pinTop, pinBottom, pinLeft, pinRight])
	}
}