VC Containment / Child View Controller hierarchy

CompositeViewController.swift

import UIKit

//I represent a screen in my app that is relatively complicated. Suppose I'm a sort of scrollable activity feed in a financial app;
//  I may have sections for balances, alerts, recent activity, credit score, a financial checkup quiz, etc.
//  Separating those sections into their own child VCs is great for splitting up the workload and separating the code.
//  Then I, the parent VC, can easily compose my feed using any subset of these child VCs and in any order using view controller containment.

class CompositeViewController: UIViewController {

  private let scrollView: UIView?
  private let contentView = UIView()

  private let creditScoreVC = CreditScoreViewController()
  private let balancesVC = BankAccountBalancesViewController()
  private let myAlertsVC = MyAlertsViewController()

  override func viewDidLoad() {
      super.viewDidLoad()
      
      scrollView = makeScrollView()
      setupChildVCs([creditScoreVC, balancesVC, myAlertsVC], constrainedToBottomOf: nil)
  }
  
  private func makeScrollView() -> UIScrollView {
    //create a UIScrollView; add + constrain contentView as its subview; return it
  }
    
  //Recursive function to contain an array of child View Controllers and lay them out vertically
  private func setupChildVCs(_ childVCs: [UIViewController], constrainedToBottomOf viewAbove: UIView?) {
      guard let childToAdd = childVCs.first, let childView = childToAdd.view else { return }

      self.addChild(childToAdd)
      contentView.addSubview(childView)

      childView.translatesAutoresizingMaskIntoConstraints = false
      NSLayoutConstraint.activate([
          childView.leadingAnchor.constraint(equalTo: contentView.leadingAnchor),
          childView.trailingAnchor.constraint(equalTo: contentView.trailingAnchor),
          childView.topAnchor.constraint(equalTo: viewAbove?.bottomAnchor ?? contentView.topAnchor)
      ])

      childToAdd.didMove(toParent: self)

      let remainingChildVCs = Array(childVCs.dropFirst())
      if remainingChildVCs.isEmpty {
          NSLayoutConstraint.activate([childView.bottomAnchor.constraint(equalTo: contentView.bottomAnchor, constant: 0)])
      } else {
          setupChildVCs(Array(childVCs.dropFirst()), constrainedToBottomOf: childView)
      }
    }
}