Architecture concept for iOS/tvOS/watchOS software in Swift
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Super Simple Architecture


Super Simple

Application Architecture you can learn in minutes.

Nobody is really smart enough to program computers.

Steve McConnell (Code Complete 2.0)

We believe we should compose software from components that are:

  • accurately named,
  • simple,
  • small,
  • responsible for one thing,
  • reusable.



  • Active Components (ex. Interaction, Navigation, Mediator etc.)
  • Passive Components (ex. Renderable)
  • Views (ex. UILabel)

🖼 Renderable

Renderable (noun)

Something (information) that view is able to show.



Renderable is a struct that you pass to a View which should show its contents.

Renderable is:

  • dead,
  • immutable struct,
  • threadsafe,
  • often converted from model or models,
  • responsible for formatting data for presentation text (ex. dates, numbers).
struct BannerRenderable {
    let message: String

View should:

  • always look the same if ordered to render the same renderable,
  • have code answering to the question: "how should I look?",
  • have no state,
  • accept infinite number of renderables in random order.


Step 1 - Create Renderable:

struct BannerRenderable {
    let message: String
    init(what: String) {
        message = "Only 🍎 has \(what)" // #courage ;)

Step 2 - Expose View ability in Protocol:

protocol BannerRendering: class {
    func render(_ renderable: BannerRenderable)

Step 2 - Implement View:

final class BannerView: UIView {
    @IBOutlet fileprivate var bannerLabel: UILabel!

extension BannerView: BannerRendering {
    func render(_ renderable: BannerRenderable) {
        bannerLabel.text = renderable.message

🛰 Interaction

**Interaction ** (noun)

Component answering the question: What should I do in reaction to user action.



Interaction is a final class that ViewController or View owns, which performs actions in reaction to user input - gestures, text input, device movement, geographical location change etc.


  • active component (has a lifecycle),
  • final class (1),
  • can use other components for data retrieval,
  • can convert Model(s) to Renderable(s) ex. via map,
  • should call render methods on weakly held views (seen via protocol).

(1) There is no good reason for inheritance of custom classes, ever.

ViewControllers and Views:

  • can have many Interactions for separate functions,
  • should OWN Interaction and see it via protocol,
  • subviews of VC could own separate Interaction but it’s not mandatory for simple VC.


Step 1 - Create Interaction protocols:

protocol PodBayDoorsInteracting: class {
    func use(_ banner: BannerRendering)
    func didTapMainButton()

Step 2 - Add Interaction implementation:

final class PodBayDoorsInteraction {
    fileprivate let killDave = true
    fileprivate weak var banner: BannerRendering?

extension PodBayDoorsInteraction: PodBayDoorsInteracting {
    private enum Strings {
        static let halsAnswer = "I know you and Frank were planning to disconnect me, and that is something I cannot allow to happen."

    func didTapMainButton() {
        guard let banner = banner else { fatalError() }

        if killDave { // Just to show the business logic is resolved here.
            banner.render(BannerRenderable(message: Strings.halsAnswer))
        } else {
            // Open doors.

    func use(_ banner: BannerRendering) {
        self.banner = banner

Step 3 - Use it in ViewController (via nib + init):

final class HAL9000ViewController: UIViewController {
    private static let nibName: String = "HAL9000ViewController"
    fileprivate let podBayInteraction: PodBayDoorsInteracting
    @IBOutlet private var bannerView: BannerRendering!
    init(podBayInteraction: PodBayDoorsInteracting) {
        self.podBayInteraction = podBayInteraction
        super.init(nibName: HAL9000ViewController.nibName, bundle: nil)
    override func awakeFromNib() {
    @IBAction private func didTapMainButton() {