iOSCleanArchitecture

iOS Clean Architecture with UIKit, MVVM, RxSwift

High level overview

The whole design architecture is separated into 4 rings:

Entities: Enterprise business rules
UseCases: Application business rules
Data: Network & Data persistent
Application: UI & Devices

The most important rule is that the inner ring knows nothing about outer ring. Which means the variables, functions and classes (any entities) that exist in the outer layers can not be mentioned in the more inward levels.

Detail overview

Domain

Entities are implemented as Swift struct

struct Article: Decodable {
    @Default.Empty var author: String
    @Default.Empty var title: String
    @Default.Empty var description: String
    @Default.Empty var url: String
    @Default.Empty var urlToImage: String
    @Default.Empty var publishedAt: String
    @Default.Empty var content: String
}

UseCases are protocols

protocol ArticleUseCase {
    func findArticlesByKeyword(_ keyword: String, pageSize: Int, page: Int) -> Single<[Article]>
}

Domain layer doesn't depend on UIKit or any 3rd party framework.

Data

Repositories are concrete implementation of UseCases

struct SearchArticleResult: Decodable {
    @Default.EmptyList var articles: [Article]
    @Default.Zero var totalResults: Int
}

struct ArticleRepository: ArticleUseCase {
    func findArticlesByKeyword(_ keyword: String, pageSize: Int, page: Int) -> Single<[Article]> {
        return ArticleService
            .searchArticlesByKeyword(q: keyword, pageSize: pageSize, page: page)
            .request(returnType: SearchArticleResult.self)
            .map { $0.articles }
    }
}

Application

Application is implemented with the MVVM pattern. The ViewModel performs pure transformation of a user Input to the Output

protocol ViewModelProtocol {
    associatedtype Input
    associatedtype Output

    func transform(input: Input) -> Output
}

struct ArticleListViewModel: ViewModelProtocol {
    struct Input {
        let search: Observable<String>
        let loadMore: Observable<Void>
    }

    struct Output {
        let tableData: Driver<[SectionModel]>
        let fetching: Driver<Bool>
        let error: Driver<Error>
    }

    @Injected var articleUseCase: ArticleUseCase

    func transform(input: Input) -> Output {
        .....
        Observable.merge(search, loadMore)
            .flatMapLatest { keyword in
                return articleUseCase
                    .findArticlesByKeyword(keyword, pageSize: pageSize, page: currentPage.value)
                    .trackActivity(activityTracker)
                    .trackError(errorTracker)
                    .asDriver(onErrorJustReturn: [])
            }
            .subscribe(onNext: { articles in
        .....
    }
}

As you can see, articleUseCase is injected to ViewModel by @Injected annotation. Thanks to Resolver library to make dependency injection easier.

The ViewModel is injected to ViewController via Navigator

struct ArticleNavigator {
    let navigationController: UINavigationController

    func showArticles() {
        let articleListViewController = Storyboard.load(.article, type: ArticleListViewController.self)
        articleListViewController.viewModel = ArticleListViewModel()
        articleListViewController.navigator = self
        navigationController.pushViewController(articleListViewController, animated: false)
    }
    .....

final class ArticleListViewController: UIViewController {
    @IBOutlet weak var tableView: UITableView!
    @IBOutlet weak var searchBar: UISearchBar!

    private let bag = DisposeBag()

    var viewModel: ArticleListViewModel!
    var navigator: ArticleNavigator!
    .....

Testing

What to test

In this architecture ViewModels, UseCases and Entities (if they contains business logic) can be tested.

ViewModel tests

To test the ViewModel you should have the RepositoryMock

struct ArticleRepositoryMock: ArticleUseCase {
    func findArticlesByKeyword(_ keyword: String, pageSize: Int, page: Int) -> Single<[Article]> {
        return MockLoader
            .load(returnType: SearchArticleResult.self, file: "searchArticles.json")
            .map { $0.articles }
    }
}

typealias ViewModel = ArticleListViewModel

class ArticleListViewModelTests: XCTestCase {

    var testScheduler: TestScheduler!
    var viewModel: ViewModel!
    let bag = DisposeBag()

    override func setUpWithError() throws {
        testScheduler = TestScheduler(initialClock: 0)
        viewModel = ArticleListViewModel()
        viewModel.articleUseCase = ArticleRepositoryMock()
    }

    override func tearDownWithError() throws {}

    func test_searchWithKeyword() throws {
        // Given
        let search = testScheduler
            .createHotObservable([
                .next(0, "Tesla")
            ])
            .asObservable()
        let input = ViewModel.Input(search: search, loadMore: .never())
        let output = viewModel.transform(input: input)

        // When
        testScheduler.start()
        let articles = try! output.tableData.articles.toBlocking().first()!

        // Then
        XCTAssertEqual(articles.count, 20)
        XCTAssertEqual(articles[1].author, "Mike Murphy")
    }

    func test_loadMore() throws {
        // Given
        let search = testScheduler
            .createHotObservable([
                .next(0, "Tesla")
            ])
            .asObservable()
        let loadMore = testScheduler
            .createHotObservable([
                .next(2, ())
            ])
            .asObservable()
        let input = ViewModel.Input(search: search, loadMore: loadMore)
        let output = viewModel.transform(input: input)

        // When
        testScheduler.start()
        let articles = try! output.tableData.articles.toBlocking().first()!
        
        // Then
        XCTAssertEqual(articles.count, 40)
    }

Code generator

The clean architecture, MVVM or VIPER will create a lot of files when you start a new module. So using a code generator is the smart way to save time.

codegen is a great tool to do it.

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