Source code for the Medium article about separating view and view controller

GenericViewController.swift

import UIKit

class GenericViewController<T: UIView>: UIViewController {

	public var rootView: T { return view as! T }

	override open func loadView() {
		self.view = T()
	}

}

MainView.swift

import UIKit

class MainView: UIView {

	let usernameHintLabel: UILabel = {
		let label = UILabel()
		label.translatesAutoresizingMaskIntoConstraints = false
		label.text = "Username"
		label.font = .systemFont(ofSize: 14, weight: .semibold)
		label.textAlignment = .left
		return label
	}()

	let usernameTextField: UITextField = {
		let textfield = UITextField()
		textfield.translatesAutoresizingMaskIntoConstraints = false
		textfield.borderStyle = .roundedRect
		textfield.placeholder = "Username"
		textfield.font = .systemFont(ofSize: 18, weight: .regular)
		return textfield
	}()

	let passwordHintLabel: UILabel = {
		let label = UILabel()
		label.translatesAutoresizingMaskIntoConstraints = false
		label.text = "Password"
		label.font = .systemFont(ofSize: 14, weight: .semibold)
		label.textAlignment = .left
		return label
	}()

	let passwordTextField: UITextField = {
		let textfield = UITextField()
		textfield.translatesAutoresizingMaskIntoConstraints = false
		textfield.borderStyle = .roundedRect
		textfield.placeholder = "Password"
		textfield.font = .systemFont(ofSize: 18, weight: .regular)
		return textfield
	}()

	let submitButton: UIButton = {
		let button = UIButton()
		button.translatesAutoresizingMaskIntoConstraints = false
		button.setTitle("Sign In", for: .normal)
		button.setTitleColor(.white, for: .normal)
		button.backgroundColor = #colorLiteral(red: 0.3647058904, green: 0.06666667014, blue: 0.9686274529, alpha: 1)
		button.layer.cornerRadius = 8
		return button
	}()

	let stackView: UIStackView = {
		let stackView = UIStackView()
		stackView.translatesAutoresizingMaskIntoConstraints = false
		stackView.alignment = .fill
		stackView.distribution = .fill
		stackView.axis = .vertical
		stackView.spacing = 8
		return stackView
	}()

	init() {
		super.init(frame: .zero)
		setup()
	}

	required init?(coder: NSCoder) {
		super.init(coder: coder)
		setup()
	}

	func setup() {
		backgroundColor = .white
		addSubview(stackView)
		addSubview(submitButton)
		[usernameHintLabel, usernameTextField, passwordHintLabel, passwordTextField].forEach { stackView.addArrangedSubview($0) }
		stackView.setCustomSpacing(16, after: usernameTextField)
		
		NSLayoutConstraint.activate([
			stackView.topAnchor.constraint(equalTo: safeAreaLayoutGuide.topAnchor, constant: 48),
			stackView.leadingAnchor.constraint(equalTo: leadingAnchor, constant: 16),
			stackView.trailingAnchor.constraint(equalTo: trailingAnchor, constant: -16),
			submitButton.leadingAnchor.constraint(equalTo: leadingAnchor, constant: 16),
			submitButton.trailingAnchor.constraint(equalTo: trailingAnchor, constant: -16),
			submitButton.bottomAnchor.constraint(equalTo: safeAreaLayoutGuide.bottomAnchor, constant: -32),
			submitButton.heightAnchor.constraint(equalToConstant: 56)
		])
	}
}

MainViewController.swift

import UIKit

class MainViewController: GenericViewController<MainView> {

	override func viewDidLoad() {
		super.viewDidLoad()
	}

	func setupTextFields() {
		rootView.usernameTextField.delegate = self
		rootView.passwordTextField.delegate = self
	}

	func setupButton() {
		rootView.submitButton.addTarget(self, action: #selector(buttonPressed), for: .primaryActionTriggered)
	}

	@objc func buttonPressed() {
		
	}

}

extension MainViewController: UITextFieldDelegate {
	
}