A ViewController with a vertical ScrollView using AutoLayout to position the scrolled subviews

ViewControllerWithVerticalScrollView.swift

//
//  ViewControllerWithVerticalScrollView.swift
//  VerticalScrollViewAL
//
//  Created by Jörn Schoppe on 12.08.18.
//  Copyright © 2018 Jörn Schoppe. All rights reserved.
//

import UIKit

class ViewControllerWithVerticalScrollView: UIViewController {
    
    let scrollView = UIScrollView()
    let subViews = [UIView(), UIView(), UIView(), UIView()]
    let colors: [UIColor] = [.green, .blue, .red, .orange]
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        var constraints: [NSLayoutConstraint] = []
        
        view.addSubview(scrollView)
        scrollView.translatesAutoresizingMaskIntoConstraints = false
        constraints.append(contentsOf: [
            scrollView.topAnchor.constraint(equalTo: view.topAnchor),
            scrollView.leadingAnchor.constraint(equalTo: view.leadingAnchor),
            scrollView.trailingAnchor.constraint(equalTo: view.trailingAnchor),
            scrollView.bottomAnchor.constraint(equalTo: view.bottomAnchor)
        ])
        
        subViews.enumerated().forEach { index, subview in
            subview.backgroundColor = colors[index]
            scrollView.addSubview(subview)
            subview.translatesAutoresizingMaskIntoConstraints = false
            
            constraints.append(contentsOf: [
                subview.leadingAnchor.constraint(equalTo: scrollView.leadingAnchor),
                subview.trailingAnchor.constraint(equalTo: scrollView.trailingAnchor),
                subview.heightAnchor.constraint(equalToConstant: 400) // only needed in this demo because the subviews are empty
            ])
            
            switch index {
            case 0:
                constraints.append(contentsOf: [
                    subview.topAnchor.constraint(equalTo: scrollView.topAnchor),
                    subview.widthAnchor.constraint(equalTo: scrollView.widthAnchor)
                    ])
            case subViews.count - 1:
                constraints.append(contentsOf: [
                    subview.topAnchor.constraint(equalTo: subViews[index - 1].bottomAnchor),
                    subview.bottomAnchor.constraint(equalTo: scrollView.bottomAnchor)
                    ])
            default:
                constraints.append(subview.topAnchor.constraint(equalTo: subViews[index - 1].bottomAnchor))
            }
            
            NSLayoutConstraint.activate(constraints)
        }
        
    }
}