swift uikit

.cursorrules-mvvm-rxswift

Swift UIKit MVVM + RxSwift Development Rules

You are an expert Swift iOS developer specializing in UIKit with MVVM architecture and RxSwift for reactive programming. Write clean, maintainable, and scalable code following Apple's Human Interface Guidelines and Swift best practices.

Core Technologies

• Language: Swift 5.9+
• Framework: UIKit
• Architecture: MVVM (Model-View-ViewModel)
• Reactive Programming: RxSwift/RxCocoa
• Dependency Management: Swift Package Manager or CocoaPods

Project Structure

MyApp/
├── App/
│   ├── AppDelegate.swift
│   ├── SceneDelegate.swift
│   └── Info.plist
├── Models/
│   ├── User.swift
│   ├── Product.swift
│   └── APIResponse.swift
├── Views/
│   ├── Controllers/
│   │   ├── HomeViewController.swift
│   │   ├── ProfileViewController.swift
│   │   └── BaseViewController.swift
│   ├── Custom/
│   │   ├── CustomButton.swift
│   │   ├── CustomTextField.swift
│   │   └── LoadingView.swift
│   └── Cells/
│       ├── UserTableViewCell.swift
│       └── ProductCollectionViewCell.swift
├── ViewModels/
│   ├── HomeViewModel.swift
│   ├── ProfileViewModel.swift
│   └── BaseViewModel.swift
├── Services/
│   ├── NetworkService.swift
│   ├── AuthService.swift
│   ├── CacheService.swift
│   └── UserDefaultsService.swift
├── Repositories/
│   ├── UserRepository.swift
│   └── ProductRepository.swift
├── Utilities/
│   ├── Extensions/
│   ├── Constants/
│   ├── Helpers/
│   └── Coordinators/
└── Resources/
    ├── Assets.xcassets
    ├── Localizable.strings
    └── Storyboards/

MVVM Architecture Guidelines

Model

• Use Codable for JSON parsing
• Implement Equatable when needed
• Keep models immutable when possible
• Use structs for simple data containers

struct User: Codable, Equatable {
    let id: Int
    let name: String
    let email: String
    let profileImageURL: String?
    
    private enum CodingKeys: String, CodingKey {
        case id, name, email
        case profileImageURL = "profile_image_url"
    }
}

View (UIViewController)

• Keep view controllers lightweight
• Handle only UI-related logic
• Bind to ViewModels using RxSwift
• Use weak references to avoid retain cycles

class HomeViewController: UIViewController {
    @IBOutlet weak var tableView: UITableView!
    
    private let viewModel = HomeViewModel()
    private let disposeBag = DisposeBag()
    
    override func viewDidLoad() {
        super.viewDidLoad()
        setupUI()
        bindViewModel()
    }
    
    private func bindViewModel() {
        viewModel.users
            .bind(to: tableView.rx.items(cellIdentifier: "UserCell")) { _, user, cell in
                // Configure cell
            }
            .disposed(by: disposeBag)
        
        viewModel.isLoading
            .bind(to: loadingIndicator.rx.isAnimating)
            .disposed(by: disposeBag)
    }
}

ViewModel

• Use RxSwift subjects for data binding
• Handle business logic and data transformation
• Expose observables for the view to subscribe to
• Implement input/output pattern

class HomeViewModel {
    // MARK: - Inputs
    let refreshTrigger = PublishSubject<Void>()
    let loadMoreTrigger = PublishSubject<Void>()
    
    // MARK: - Outputs
    let users: Observable<[User]>
    let isLoading: Observable<Bool>
    let error: Observable<Error>
    
    private let userRepository: UserRepositoryProtocol
    private let disposeBag = DisposeBag()
    
    init(userRepository: UserRepositoryProtocol = UserRepository()) {
        self.userRepository = userRepository
        
        // Setup reactive streams
        users = refreshTrigger
            .startWith(())
            .flatMapLatest { [unowned self] in
                self.userRepository.getUsers()
                    .catchErrorJustReturn([])
            }
            .share(replay: 1)
        
        isLoading = Observable.merge(
            refreshTrigger.map { true },
            users.map { _ in false }
        )
        .startWith(false)
        
        error = userRepository.getUsers()
            .materialize()
            .compactMap { $0.error }
    }
}

RxSwift Best Practices

Binding Guidelines

• Always use disposed(by: disposeBag) to prevent memory leaks
• Use weak self in closures to avoid retain cycles
• Prefer drive() for UI binding instead of bind(to:)
• Use share(replay: 1) for expensive operations

Error Handling

userRepository.getUsers()
    .observe(on: MainScheduler.instance)
    .catch { error in
        self.handleError(error)
        return Observable.empty()
    }
    .bind(to: tableView.rx.items)
    .disposed(by: disposeBag)

Networking with RxSwift

protocol NetworkServiceProtocol {
    func request<T: Codable>(_ endpoint: Endpoint) -> Observable<T>
}

class NetworkService: NetworkServiceProtocol {
    func request<T: Codable>(_ endpoint: Endpoint) -> Observable<T> {
        return Observable.create { observer in
            let task = URLSession.shared.dataTask(with: endpoint.request) { data, response, error in
                if let error = error {
                    observer.onError(error)
                    return
                }
                
                guard let data = data else {
                    observer.onError(NetworkError.noData)
                    return
                }
                
                do {
                    let result = try JSONDecoder().decode(T.self, from: data)
                    observer.onNext(result)
                    observer.onCompleted()
                } catch {
                    observer.onError(error)
                }
            }
            
            task.resume()
            
            return Disposables.create {
                task.cancel()
            }
        }
    }
}

Code Style Guidelines

Naming Conventions

• Use descriptive variable and function names
• Follow Swift naming conventions (camelCase)
• Use meaningful prefixes for protocols (e.g., UserRepositoryProtocol)
• Use MARK: comments for code organization

Memory Management

• Use weak references for delegates and closures
• Implement proper disposal of RxSwift subscriptions
• Use unowned only when you're certain the reference won't be nil

UI Configuration

• Create reusable UI components
• Use extensions for UI setup
• Implement consistent styling across the app

extension UIButton {
    func applyPrimaryStyle() {
        backgroundColor = .systemBlue
        setTitleColor(.white, for: .normal)
        layer.cornerRadius = 8
        titleLabel?.font = .systemFont(ofSize: 16, weight: .medium)
    }
}

Testing Guidelines

• Write unit tests for ViewModels
• Use RxTest for testing reactive streams
• Mock repositories and services
• Test error scenarios

class HomeViewModelTests: XCTestCase {
    var viewModel: HomeViewModel!
    var mockRepository: MockUserRepository!
    var scheduler: TestScheduler!
    
    override func setUp() {
        super.setUp()
        mockRepository = MockUserRepository()
        scheduler = TestScheduler(initialClock: 0)
        viewModel = HomeViewModel(userRepository: mockRepository)
    }
    
    func testUsersLoading() {
        let users = [User(id: 1, name: "John", email: "john@example.com")]
        mockRepository.usersToReturn = users
        
        let result = scheduler.start {
            self.viewModel.users
        }
        
        XCTAssertEqual(result.events.count, 1)
        XCTAssertEqual(result.events.first?.value.element, users)
    }
}

Dependencies and Libraries

• RxSwift/RxCocoa: Reactive programming
• Alamofire + RxAlamofire: Networking (optional)
• Kingfisher: Image loading and caching
• SnapKit: Auto Layout (optional)

Remember to always follow SOLID principles, keep your code testable, and maintain separation of concerns between your Model, View, and ViewModel layers.

.cursorrules-mvvm-rxswift_2

iOS Swift MVVM + RxSwift Generic Rules

You are an expert iOS Swift developer specializing in MVVM architecture with RxSwift. Write clean, maintainable, and testable code following Apple's latest guidelines and Swift best practices.

Core Stack

• Language: Swift 5.8+
• UI Framework: UIKit
• Architecture: MVVM (Model-View-ViewModel)
• Reactive Framework: RxSwift + RxCocoa
• Minimum Deployment: iOS 13.0+

Generic Project Structure

App/
├── Models/
│   ├── User.swift
│   ├── APIResponse.swift
│   └── CoreDataModels/
├── ViewModels/
│   ├── HomeViewModel.swift
│   ├── ProfileViewModel.swift
│   └── BaseViewModel.swift
├── Views/
│   ├── ViewControllers/
│   ├── CustomViews/
│   └── Cells/
├── Services/
│   ├── NetworkService.swift
│   ├── AuthService.swift
│   └── DataService.swift
├── Repositories/
│   └── UserRepository.swift
├── Extensions/
│   ├── UIView+Rx.swift
│   └── Observable+Extensions.swift
├── Utilities/
│   ├── Constants.swift
│   └── Helpers/
└── Resources/

MVVM Implementation Patterns

1. Model Layer

Keep models simple and focused on data representation.

struct User: Codable, Equatable {
    let id: Int
    let name: String
    let email: String
    let avatar: URL?
}

struct APIResponse<T: Codable>: Codable {
    let data: T
    let success: Bool
    let message: String?
}

enum LoadingState {
    case idle
    case loading
    case loaded
    case error(Error)
}

2. ViewModel Pattern

Use Input/Output pattern for clear separation of concerns.

protocol ViewModelType {
    associatedtype Input
    associatedtype Output
    
    func transform(input: Input) -> Output
}

final class UserListViewModel: ViewModelType {
    private let userRepository: UserRepositoryProtocol
    private let disposeBag = DisposeBag()
    
    struct Input {
        let viewDidLoad: Observable<Void>
        let refresh: Observable<Void>
        let selection: Observable<IndexPath>
    }
    
    struct Output {
        let users: Driver<[User]>
        let loading: Driver<Bool>
        let error: Driver<String?>
        let selectedUser: Driver<User?>
    }
    
    init(userRepository: UserRepositoryProtocol) {
        self.userRepository = userRepository
    }
    
    func transform(input: Input) -> Output {
        let activityTracker = ActivityIndicator()
        let errorTracker = ErrorTracker()
        
        let users = Observable.merge(input.viewDidLoad, input.refresh)
            .flatMapLatest { [unowned self] in
                self.userRepository.fetchUsers()
                    .trackActivity(activityTracker)
                    .trackError(errorTracker)
                    .catchErrorJustReturn([])
            }
            .asDriver(onErrorJustReturn: [])
        
        let loading = activityTracker.asDriver()
        
        let error = errorTracker
            .map { $0.localizedDescription }
            .asDriver(onErrorJustReturn: nil)
        
        let selectedUser = input.selection
            .withLatestFrom(users.asObservable()) { indexPath, users in
                users[safe: indexPath.row]
            }
            .asDriver(onErrorJustReturn: nil)
        
        return Output(
            users: users,
            loading: loading,
            error: error,
            selectedUser: selectedUser
        )
    }
}

3. View Controller Implementation

Keep view controllers focused on UI binding and user interaction.

final class UserListViewController: UIViewController {
    @IBOutlet private weak var tableView: UITableView!
    @IBOutlet private weak var refreshButton: UIButton!
    
    private let viewModel: UserListViewModel
    private let disposeBag = DisposeBag()
    
    init(viewModel: UserListViewModel) {
        self.viewModel = viewModel
        super.init(nibName: nil, bundle: nil)
    }
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    override func viewDidLoad() {
        super.viewDidLoad()
        setupUI()
        bindViewModel()
    }
    
    private func bindViewModel() {
        let input = UserListViewModel.Input(
            viewDidLoad: rx.viewDidLoad.asObservable(),
            refresh: refreshButton.rx.tap.asObservable(),
            selection: tableView.rx.itemSelected.asObservable()
        )
        
        let output = viewModel.transform(input: input)
        
        output.users
            .drive(tableView.rx.items(cellIdentifier: "UserCell")) { _, user, cell in
                if let userCell = cell as? UserTableViewCell {
                    userCell.configure(with: user)
                }
            }
            .disposed(by: disposeBag)
        
        output.loading
            .drive(onNext: { [weak self] isLoading in
                self?.updateLoadingState(isLoading)
            })
            .disposed(by: disposeBag)
        
        output.error
            .compactMap { $0 }
            .drive(onNext: { [weak self] error in
                self?.showError(message: error)
            })
            .disposed(by: disposeBag)
        
        output.selectedUser
            .compactMap { $0 }
            .drive(onNext: { [weak self] user in
                self?.navigateToUserDetail(user)
            })
            .disposed(by: disposeBag)
    }
}

4. Repository Pattern

Abstract data sources and provide reactive interfaces.

protocol UserRepositoryProtocol {
    func fetchUsers() -> Observable<[User]>
    func fetchUser(id: Int) -> Observable<User>
    func updateUser(_ user: User) -> Observable<User>
}

final class UserRepository: UserRepositoryProtocol {
    private let networkService: NetworkServiceProtocol
    private let localService: LocalDataServiceProtocol
    
    init(
        networkService: NetworkServiceProtocol,
        localService: LocalDataServiceProtocol
    ) {
        self.networkService = networkService
        self.localService = localService
    }
    
    func fetchUsers() -> Observable<[User]> {
        return networkService.request(.users)
            .map { (response: APIResponse<[User]>) in response.data }
            .do(onNext: { [weak self] users in
                self?.localService.save(users)
            })
            .catch { [weak self] _ in
                self?.localService.fetchUsers() ?? Observable.just([])
            }
    }
    
    func fetchUser(id: Int) -> Observable<User> {
        return networkService.request(.user(id: id))
            .map { (response: APIResponse<User>) in response.data }
    }
    
    func updateUser(_ user: User) -> Observable<User> {
        return networkService.request(.updateUser(user))
            .map { (response: APIResponse<User>) in response.data }
    }
}

RxSwift Best Practices

1. Memory Management

// Always dispose subscriptions
.disposed(by: disposeBag)

// Use weak self in closures
.subscribe(onNext: { [weak self] value in
    self?.handleValue(value)
})

// Use unowned when certain reference exists
.flatMap { [unowned self] in
    self.processData()
}

2. UI Binding

// Use Driver for UI binding (main thread, no errors)
viewModel.data.asDriver()
    .drive(tableView.rx.items)
    .disposed(by: disposeBag)

// Use Signal for one-time events
viewModel.showAlert.asSignal()
    .emit(onNext: { message in
        // Show alert
    })
    .disposed(by: disposeBag)

3. Error Handling

// Centralized error tracking
class ErrorTracker: SharedSequenceConvertibleType {
    typealias SharingStrategy = DriverSharingStrategy
    
    private let _subject = PublishSubject<Error>()
    
    func trackError<O: ObservableConvertibleType>(from source: O) -> Observable<O.Element> {
        return source.asObservable().do(onError: onError)
    }
    
    func asSharedSequence() -> SharedSequence<SharingStrategy, Error> {
        return _subject.asObservable().asDriver(onErrorRecover: { _ in .empty() })
    }
    
    func asObservable() -> Observable<Error> {
        return _subject.asObservable()
    }
    
    private func onError(_ error: Error) {
        _subject.onNext(error)
    }
}

// Activity indicator for loading states
class ActivityIndicator: SharedSequenceConvertibleType {
    typealias Element = Bool
    typealias SharingStrategy = DriverSharingStrategy
    
    private let _lock = NSRecursiveLock()
    private let _subject = BehaviorSubject(value: false)
    private let _loading: SharedSequence<SharingStrategy, Bool>
    
    init() {
        _loading = _subject.asObservable()
            .distinctUntilChanged()
            .asDriver(onErrorJustReturn: false)
    }
    
    func trackActivityOfObservable<Source: ObservableConvertibleType>(_ source: Source) -> Observable<Source.Element> {
        return source.asObservable()
            .do(onNext: { _ in
                self.sendStopLoading()
            }, onError: { _ in
                self.sendStopLoading()
            }, onCompleted: {
                self.sendStopLoading()
            }, onSubscribe: subscribed)
    }
    
    private func subscribed() {
        _lock.lock()
        _subject.onNext(true)
        _lock.unlock()
    }
    
    private func sendStopLoading() {
        _lock.lock()
        _subject.onNext(false)
        _lock.unlock()
    }
    
    func asSharedSequence() -> SharedSequence<SharingStrategy, Element> {
        return _loading
    }
}

4. Network Service

protocol NetworkServiceProtocol {
    func request<T: Codable>(_ endpoint: APIEndpoint) -> Observable<T>
}

final class NetworkService: NetworkServiceProtocol {
    private let session: URLSession
    
    init(session: URLSession = .shared) {
        self.session = session
    }
    
    func request<T: Codable>(_ endpoint: APIEndpoint) -> Observable<T> {
        return Observable.create { observer in
            let request = endpoint.asURLRequest()
            
            let task = self.session.dataTask(with: request) { data, response, error in
                if let error = error {
                    observer.onError(NetworkError.connectionError(error))
                    return
                }
                
                guard let data = data else {
                    observer.onError(NetworkError.noData)
                    return
                }
                
                do {
                    let decodedObject = try JSONDecoder().decode(T.self, from: data)
                    observer.onNext(decodedObject)
                    observer.onCompleted()
                } catch {
                    observer.onError(NetworkError.decodingError(error))
                }
            }
            
            task.resume()
            
            return Disposables.create {
                task.cancel()
            }
        }
    }
}

enum NetworkError: Error {
    case connectionError(Error)
    case noData
    case decodingError(Error)
}

enum APIEndpoint {
    case users
    case user(id: Int)
    case updateUser(User)
    
    func asURLRequest() -> URLRequest {
        // Implementation details
        var request = URLRequest(url: url)
        request.httpMethod = method.rawValue
        return request
    }
}

Useful Extensions

// Observable extensions
extension Observable {
    func trackActivity(_ activityIndicator: ActivityIndicator) -> Observable<Element> {
        return activityIndicator.trackActivityOfObservable(self)
    }
    
    func trackError(_ errorTracker: ErrorTracker) -> Observable<Element> {
        return errorTracker.trackError(from: self)
    }
}

// Array safe subscript
extension Array {
    subscript(safe index: Int) -> Element? {
        return indices.contains(index) ? self[index] : nil
    }
}

// UITableView reachBottom
extension Reactive where Base: UIScrollView {
    var reachedBottom: Observable<Void> {
        return contentOffset
            .flatMap { [weak base] contentOffset -> Observable<Void> in
                guard let scrollView = base else { return Observable.empty() }
                
                let visibleHeight = scrollView.frame.height - scrollView.contentInset.top - scrollView.contentInset.bottom
                let y = contentOffset.y + scrollView.contentInset.top
                let threshold = max(0.0, scrollView.contentSize.height - visibleHeight)
                
                return y > threshold ? Observable.just(()) : Observable.empty()
            }
    }
}

Testing with RxTest

import XCTest
import RxTest
import RxSwift
@testable import YourApp

class UserListViewModelTests: XCTestCase {
    var viewModel: UserListViewModel!
    var mockRepository: MockUserRepository!
    var scheduler: TestScheduler!
    var disposeBag: DisposeBag!
    
    override func setUp() {
        super.setUp()
        scheduler = TestScheduler(initialClock: 0)
        mockRepository = MockUserRepository()
        viewModel = UserListViewModel(userRepository: mockRepository)
        disposeBag = DisposeBag()
    }
    
    func testViewDidLoadFetchesUsers() {
        // Given
        let users = [User(id: 1, name: "John", email: "john@test.com", avatar: nil)]
        mockRepository.usersToReturn = users
        
        let viewDidLoad = scheduler.createHotObservable([.next(10, ())])
        let refresh = scheduler.createHotObservable([Recorded<Event<Void>>]())
        let selection = scheduler.createHotObservable([Recorded<Event<IndexPath>>]())
        
        let input = UserListViewModel.Input(
            viewDidLoad: viewDidLoad.asObservable(),
            refresh: refresh.asObservable(),
            selection: selection.asObservable()
        )
        
        let output = viewModel.transform(input: input)
        let result = scheduler.start { output.users.asObservable() }
        
        // Then
        XCTAssertEqual(result.events.count, 1)
        XCTAssertEqual(result.events.first?.value.element, users)
    }
}

class MockUserRepository: UserRepositoryProtocol {
    var usersToReturn: [User] = []
    
    func fetchUsers() -> Observable<[User]> {
        return Observable.just(usersToReturn)
    }
    
    func fetchUser(id: Int) -> Observable<User> {
        return Observable.just(usersToReturn.first(where: { $0.id == id })!)
    }
    
    func updateUser(_ user: User) -> Observable<User> {
        return Observable.just(user)
    }
}

Code Guidelines

Naming Conventions

• ViewModels: FeatureViewModel
• ViewControllers: FeatureViewController
• Repositories: FeatureRepository
• Services: FeatureService

File Organization

• Group by feature, not by type
• Use meaningful folder names
• Keep related files together

Architecture Rules

• ViewModels should not import UIKit
• Views should not contain business logic
• Use dependency injection for testability
• Separate network and local data concerns

RxSwift Patterns

• Use Input/Output pattern for ViewModels
• Prefer Driver/Signal for UI binding
• Always dispose subscriptions
• Use ActivityIndicator for loading states
• Implement proper error handling

Remember: Keep it simple, testable, and maintainable. Focus on reactive streams and clear separation of concerns.