Example of ViewController container

ViewControllerContainer.swift

import UIKit
import PlaygroundSupport

let screenHeight: CGFloat = 400
let screenWidth: CGFloat = 200

class InnerViewController: UIViewController {
    var stack: UIStackView = {
        var label: UILabel {
            let label = UILabel()
            label.text = "testing"
            return label
        }
        
        let stack = UIStackView()
        stack.axis = .vertical
        stack.backgroundColor = .red
        stack.addArrangedSubview(label)
        stack.addArrangedSubview(label)
        stack.translatesAutoresizingMaskIntoConstraints = false
        return stack
    }()
    
    override func viewDidLoad() {
        super.viewDidLoad()
        view.backgroundColor = .gray
        view.addSubview(stack)
        
        stack.leadingAnchor.constraint(equalTo: view.leadingAnchor).isActive = true
        stack.trailingAnchor.constraint(equalTo: view.trailingAnchor).isActive = true
        stack.topAnchor.constraint(equalTo: view.topAnchor).isActive = true
        stack.bottomAnchor.constraint(equalTo: view.bottomAnchor).isActive = true
    }
}

class ViewController: UIViewController {
    var viewContainer: UIView = {
        let view = UIView()
        view.translatesAutoresizingMaskIntoConstraints = false
        view.backgroundColor = .cyan
        return view
    }()
    
    override func viewDidLoad() {
        super.viewDidLoad()
        view.backgroundColor = .gray
    }
    
    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)
        setupViewContainer()
        addViewController(vc: InnerViewController())
    }
    
    func setupViewContainer() {
        view.addSubview(viewContainer)
        viewContainer.leadingAnchor.constraint(equalTo: view.leadingAnchor).isActive = true
        viewContainer.trailingAnchor.constraint(equalTo: view.trailingAnchor).isActive = true
        viewContainer.topAnchor.constraint(equalTo: view.topAnchor).isActive = true
        viewContainer.bottomAnchor.constraint(lessThanOrEqualTo: view.bottomAnchor).isActive = true
    }
    
    func addViewController(vc: UIViewController) {
        vc.view.translatesAutoresizingMaskIntoConstraints = false
        self.addChild(vc)
        viewContainer.addSubview(vc.view)
        vc.didMove(toParent: self)
        
        vc.view.leadingAnchor.constraint(equalTo: viewContainer.leadingAnchor).isActive = true
        vc.view.trailingAnchor.constraint(equalTo: viewContainer.trailingAnchor).isActive = true
        vc.view.topAnchor.constraint(equalTo: viewContainer.topAnchor).isActive = true
        vc.view.bottomAnchor.constraint(equalTo: viewContainer.bottomAnchor).isActive = true
    }
}

let vc = ViewController()
vc.view.frame = CGRect(x: 0, y: 0, width: screenWidth, height: screenHeight)

PlaygroundPage.current.needsIndefiniteExecution = true
PlaygroundPage.current.liveView = vc