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---
layout: default
title: iOS Architecture Patterns
categories: swift
---
### Remove story board dependency
1. Remove `Main.storyboard` file
1. Remove storyboard reference from `Info.plist` → In Scene Configuration find `Storyboard Name` and delete it
1. Go to build settings and remove `UIKit MainStoryboard File Base Name` field
1. Create a window in Scene Delegate
```swift
func scene(_ scene: UIScene,
willConnectTo session: UISceneSession,
options connectionOptions: UIScene.ConnectionOptions) {
guard let scene = (scene as? UIWindowScene) else { return }
let window = UIWindow(windowScene: scene)
window.rootViewController = ViewController()
window.makeKeyAndVisible()
self.window = window
}
```
## Dependency injection
<!-- https://www.swiftbysundell.com/tips/testing-code-that-uses-static-apis/ -->
[Explanation of the code under this link](https://www.avanderlee.com/swift/dependency-injection/)
```swift
public protocol InjectionKey {
associatedtype Value
static var currentValue: Self.Value { get set }
}
```
```swift
struct InjectedValues {
private static var current = InjectedValues()
static subscript<K>(key: K.Type) -> K.Value where K : InjectionKey {
get { key.currentValue }
set { key.currentValue = newValue }
}
static subscript<T>(_ keyPath: WritableKeyPath<InjectedValues, T>) -> T {
get { current[keyPath: keyPath] }
set { current[keyPath: keyPath] = newValue }
}
}
```
```swift
@propertyWrapper
struct Injected<T> {
private let keyPath: WritableKeyPath<InjectedValues, T>
var wrappedValue: T {
get { InjectedValues[keyPath] }
set { InjectedValues[keyPath] = newValue }
}
init(_ keyPath: WritableKeyPath<InjectedValues, T>) {
self.keyPath = keyPath
}
}
```
#### Define dependency
```swift
private struct UsersRepositoryKey: InjectionKey {
static var currentValue: AnyUsersRepository = UsersRepository()
}
extension InjectedValues {
var usersRepository: AnyUsersRepository {
get { Self[UsersRepositoryKey.self] }
set { Self[UsersRepositoryKey.self] = newValue }
}
}
protocol AnyUsersRepository {
func getUsers(_ result: @escaping (Result<[User], Error>)->Void)
}
class UsersRepository: AnyUsersRepository {
func getUsers(_ result: @escaping (Result<[User], Error>)->Void) {
<#Implementation#>
}
}
```
```swift
@Injected(\.usersRepository) var usersRepository: AnyUsersRepository
```
```swift
InjectedValues[\.usersRepository] = MockedUsersRepository()
```
## Model-View-Controller
#### Clasic version
- `View` and `Model` are linked together, so reusability is reduced.
- Note: Views in iOS apps are quite often reusable.
<p>
{% svg ../svgs/classic-mvc.svg class="center-image" %}
</p>
#### Apple version
<p>
{% svg ../svgs/apple-mvc.svg class="center-image" %}
</p>
**Model** responsibilities:
- Business logic
- Accessing and manipulating data
- Persistence
- Communication/Networking
- Parsing
- Extensions and helper classes
- Communication with models
Note: The `Model` must not communicate directly with the `View`. The `Controller` is the link between those
**View** responsibilities:
- Animations, drawings (`UIView`, `CoreAnimation`, `CoreGraphics`)
- Show data that controller sends
- Might receive user input
**Controller** responsibilities:
- Exchange data between `View` and `Model`
- Receive user actions and interruptions or signals from the outside the app
- Handles the view life cycle
#### Advantages
- Simple and usually less code
- Fast development for simple apps
#### Disadvantages
- Controllers coupled views
- Massive `ViewController`s
#### Communication between components
- [Delegation](https://developer.apple.com/library/archive/documentation/General/Conceptual/Devpedia-CocoaApp/TargetAction.html) pattern
- [Target-Action](https://developer.apple.com/library/archive/documentation/General/Conceptual/Devpedia-CocoaApp/TargetAction.html) pattern
- [Observer](https://developer.apple.com/documentation/foundation/nsnotificationcenter) pattern with `NSNotificationCenter`
- [Observer](https://developer.apple.com/documentation/swift/using-key-value-observing-in-swift) pattern with `KVO`
## Model-View-Presenter
In this design pattern View is implemented with classes `UIView` and `UIViewController`. The `UIViewController` has less responsibilities which are limited to:
- Routing/Coordination
- Navigation
- Passing informations via a delegation pattern
#### View
```swift
class ExampleController: UIViewController {
private let exampleView = ExampleView()
override func loadView() {
super.loadView()
setup()
}
private func setup() {
let presenter = ExamplePresenter(exampleView)
exampleView.presenter = presenter
exampleView.setupView()
self.view = exampleView
}
}
```
#### Presenter
```swift
protocol ExampleViewDelegate {
func updateView()
}
class ExamplePresenter {
private weak var exampleView: ExampleViewDelegate?
init(_ exampleView: ExampleViewDelegate) {
self.exampleView = exampleView
}
}
```
#### Advantages
- Easier to test business logic
- Better separation of responsibilities
#### Disadvantages
- Usually not a better choice for smaller projects
- Presenters might become massive
- Controllers still handle navigation. Possible solutions &rarr; extend the pattern with Router or Coordinator.
#### Common layers
- Data access layer: `CRUD` operations facilitated with `CoreData` `Realm` etc.
- Services: Classes that interacts with database entities, like retrieve data, transform them into objects.
- Extensions/utils
## Model-View-ViewModel
`ViewModel` has no references to the view.
<p>
{% svg ../svgs/mvvm.svg class="center-image" %}
</p>
Binding is done using: `Combine Framework`, `RxSwift`, `Bond` or `KVO` or using delegation pattern
* **`Model`** does same things as in `MVP` and `MVC`.
* **`View`** also is similar, but binds with `ViewModel`
* **`ViewModel`** keeps updated state of the view, and process data for i
#### Advantages
- Better reparation of responsibilities
- Better testability, without needing to take into account the views
#### Disadvantages
- Might be slower and introduce dependency on external libraries
- Harder to learn and can become complex
#### **Extension with Coordinator MVVM-C**
Role of `Coordinator` is to manage navigation flow.
```swift
protocol Coordinator {
var navigationController: UINavigationController { get set }
func start()
}
```
and an example implementation
```swift
class ExampleCoordinator: Coordinator {
var navigationController: UINavigationController
init(navigationController: UINavigationController) {
self.navigationController = UINavigationController
}
func start() {
let viewModel = ExampleViewModel(someService: SomeService(),
coordinator: self)
navigationController.pushViewController(ExampleController(viewModel),
animated: true)
}
func showList(_ list: ExampleListModel) {
let listCoordinator = ListCoordinator(navigationController: navigationController
list: list)
listCoordinator.start()
}
}
```
In the book I am reading the author created an `ExampleCoordinatorProtocol` with a `func showList(_ list: ExampleListModel)` where the `ExampleCoordinator` implemented it. I think it does not make any sense, however if we might want to inject the coordinator then we might want to relay on an abstraction.
```swift
func scene(_ scene: UIScene,
willConnectTo session: UISceneSession,
options connectionOptions: UIScene.ConnectionOptions) {
guard let scene = (scene as? UIWindowScene) else { return }
let window = UIWindow(windowScene: scene)
let navigationController = UINavigationController()
exampleCoordinator = ExampleCoordinator(navigationController: navigationController)
exampleCoordinator?.start()
window.rootViewController = navigationController
window.makeKeyAndVisible()
self.window = window
}
```
## VIPER
<p>
{% svg ../svgs/viper-ownership.svg class="center-image" %}
</p>
#### View
It includes `UIViewController`
- Made only to preserve elements like Buttons Labels
- It sends informations to presenters, and receive messages what to show and knows how
#### Interactor
- Receives informations form databases, servers etc.
- The book says that the Interactor receive actions from presenter, and returns the result via Delegation Pattern.
- The interactor never sends entities to the Presenter
#### Presenter
- Is in the centre and serves as a link
- Process events from the view and requests data from the Interctor. It receives that as primitives, never Entities.
- it handles navigation to the other screens using the Router
#### Entity
- Simple models usually data structures
- They can only be used by the Interactor
#### Router
- Creates screens
- Handles navigation, but itself does not know where to go to.
- _The book says it is the owner of the `UINavigationController` and UIViewController, but it is contrary to other parts of the book, so I do not know_
- Similar to `Coordinator` form MVVM-C
<!--
https://github.com/ochococo/Design-Patterns-In-Swift
https://nalexn.github.io/clean-architecture-swiftui/
https://medium.com/@vladislavshkodich/architectures-comparing-for-swiftui-6351f1fb3605
-->
**`Entity.swift`**
```swift
struct User: Codable {
let name: String
}
```
**`Interactor.swift`**
```swift
enum FetchError: Error {
case failed
}
protocol AnyInteractor {
var presenter: AnyPresenter? { get set }
func getUsers()
}
class UserInteractor: AnyInteractor {
@Injected(\.usersRepository) var usersRepository: AnyUsersRepository
var presenter: AnyPresenter?
func getUsers() {
usersRepository.getUsers { [weak self] in self?.presenter?.interactorDidFetchUsers(with: $0) }
}
}
```
**`Presenter.swift`**
```swift
protocol AnyPresenter {
var router: AnyRouter? { get set }
var interactor: AnyInteractor? { get set }
var view: AnyView? { get set }
func interactorDidFetchUsers(with result: Result<[User], Error>)
}
class UserPresenter: AnyPresenter {
func interactorDidFetchUsers(with result: Result<[User], Error>) {
switch result {
case let .success(users):
view?.update(with: users)
case let .failure(error):
view?.update(with: error.localizedDescription)
}
}
var router: AnyRouter?
var interactor: AnyInteractor? {
didSet {
interactor?.getUsers()
}
}
var view: AnyView?
}
```
**`Router.swift`**
```swift
typealias EntryPoint = AnyView & UIViewController
protocol AnyRouter {
var entry: EntryPoint? { get }
static func start() -> AnyRouter
}
class UserRouter: AnyRouter {
var entry: EntryPoint?
static func start() -> AnyRouter {
let router = UserRouter()
var view: AnyView = UserViewController()
var presenter: AnyPresenter = UserPresenter()
var interactor: AnyInteractor = UserInteractor()
view.presenter = presenter
interactor.presenter = presenter
presenter.router = router
presenter.view = view
presenter.interactor = interactor
router.entry = view as? EntryPoint
return router
}
}
//There are a few retain cycles with view, presenter, router and interactor. One option you can do is to make those protocols conforms to AnyObject, and mark these references as "weak":
//1. router's ref to presenter
//2. router's ref to view
//3. presenter's ref to view
//4. interactor's ref to presenter
```
**`View.swift`**
```swift
protocol AnyView {
var presenter: AnyPresenter? { get set }
func update(with users: [User])
func update(with error: String)
}
class UserViewController: UIViewController, AnyView {
var presenter: AnyPresenter?
private let tableView: UITableView = {
let tableView = UITableView()
tableView.register(UITableViewCell.self, forCellReuseIdentifier: "cell")
tableView.isHidden = true
return tableView
}()
var users = [User]()
override func viewDidLoad() {
super.viewDidLoad()
view.addSubview(tableView)
tableView.delegate = self
tableView.dataSource = self
}
override func viewDidLayoutSubviews() {
super.viewDidLayoutSubviews()
tableView.frame = view.bounds
}
func update(with users: [User]) {
DispatchQueue.main.async {
self.users = users
self.tableView.reloadData()
self.tableView.isHidden = false
}
}
func update(with error: String) {
}
}
extension UserViewController: UITableViewDelegate, UITableViewDataSource {
func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
users.count
}
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCell(withIdentifier: "cell", for: indexPath)
cell.textLabel?.text = users[indexPath.row].name
return cell
}
}
```
<!--
RIBs
https://github.com/uber/RIBs
https://medium.com/swlh/ios-architecture-exploring-ribs-3db765284fd8
https://github.com/uber/RIBs/wiki
-->
<!--
redux
https://medium.com/mackmobile/getting-started-with-redux-in-swift-54e00f323e2b
-->
<!--
# Factory
```swift
protocol ImageReader {
func getDecodeImage() -> DecodedImage
}
class DecodedImage {
private var image: String
init(image: String) {
self.image = image
}
var description: String {
"\(image): is decoded"
}
}
class GifReader: ImageReader {
private var decodedImage: DecodedImage
init(image: String) {
self.decodedImage = DecodedImage(image: image)
}
func getDecodeImage() -> DecodedImage {
decodedImage
}
}
class JpegReader: ImageReader {
private var decodedImage: DecodedImage
init(image: String) {
decodedImage = DecodedImage(image: image)
}
func getDecodeImage() -> DecodedImage {
decodedImage
}
}
func runFactoryExample() {
let reader: ImageReader
let format = "gif"
let image = "example image"
switch format {
case "gif":
reader = GifReader(image: image)
default:
reader = JpegReader(image: image)
}
let decodedImage = reader.getDecodeImage()
print(decodedImage.description)
}
```
```swift
protocol Observer<ValueType> {
associatedtype ValueType
func update(value: ValueType)
}
struct Subject<T> {
private var observers: [(T) -> Void] = []
mutating func attach<O: Observer>(observer: O) where O.ValueType == T {
observers.append { observer.update(value: $0) }
}
func notyfi(value: T) {
for observer in observers {
observer(value)
}
}
}
class ConcreteObserver: Observer {
func update(value: String) {
print("received: \(value)")
}
}
func runObserverExample() {
var subject = Subject<String>()
let observer1 = ConcreteObserver()
subject.attach(observer: observer1)
let observer2 = ConcreteObserver()
subject.attach(observer: observer2)
subject.notyfi(value: "some string")
}
// Version with more modern syntax
/*
protocol Observer<ValueType> {
associatedtype ValueType
func update(value: ValueType)
}
struct Subject<T> {
private var observers = Array<any Observer<T>>()
mutating func attach(observer: any Observer<T>) {
observers.append(observer)
}
func notify(value: T) {
for observer in observers {
observer.update(value: value)
}
}
}
*/
```
-->