Cursor rules for Swift Uikit.
.cursorrules or .cursor/rules/swift-uikit.mdc # .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
```swift
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
```swift
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
```swift
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
```swift
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
```swift
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
```swift
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
```swift
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.
```swift
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.
```swift
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.
```swift
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.
```swift
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
```swift
// 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
```swift
// 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
```swift
// 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
```swift
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
```swift
// 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
```swift
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. 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.
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/
Codable for JSON parsingEquatable when neededstruct 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"
}
}
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)
}
}
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 }
}
}
disposed(by: disposeBag) to prevent memory leaksweak self in closures to avoid retain cyclesdrive() for UI binding instead of bind(to:)share(replay: 1) for expensive operationsuserRepository.getUsers()
.observe(on: MainScheduler.instance)
.catch { error in
self.handleError(error)
return Observable.empty()
}
.bind(to: tableView.rx.items)
.disposed(by: disposeBag)
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()
}
}
}
}
UserRepositoryProtocol)MARK: comments for code organizationweak references for delegates and closuresunowned only when you’re certain the reference won’t be nilextension UIButton {
func applyPrimaryStyle() {
backgroundColor = .systemBlue
setTitleColor(.white, for: .normal)
layer.cornerRadius = 8
titleLabel?.font = .systemFont(ofSize: 16, weight: .medium)
}
}
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)
}
}
Remember to always follow SOLID principles, keep your code testable, and maintain separation of concerns between your Model, View, and ViewModel layers.
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.
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/
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)
}
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
)
}
}
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)
}
}
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 }
}
}
// 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()
}
// 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)
// 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
}
}
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
}
}
// 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()
}
}
}
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)
}
}
FeatureViewModelFeatureViewControllerFeatureRepositoryFeatureServiceRemember: Keep it simple, testable, and maintainable. Focus on reactive streams and clear separation of concerns.
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