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Zhongwei Li
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skills/ios-code-review/examples.md
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skills/ios-code-review/examples.md
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# iOS Code Review Examples
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Detailed examples for each review category with good/bad patterns.
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## 1. Naming Conventions Examples
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### ✅ Good Naming
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```swift
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// Classes and Types
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class PaymentViewController: UIViewController { }
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class RefundRequestViewModel: BaseViewModel<RefundRequestState> { }
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protocol PaymentUseCase { }
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// Variables and Properties
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let paymentAmount = BehaviorRelay<String>(value: "")
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let isProcessingPayment = BehaviorRelay<Bool>(value: false)
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let transactions = BehaviorRelay<[Transaction]>(value: [])
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// Functions
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func loadTransactions() { }
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func processPaymentRequest(amount: Double) { }
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func validatePaymentAmount(_ amount: String) -> Bool { }
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// IBOutlets
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@IBOutlet weak var paymentAmountTextField: UITextField!
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@IBOutlet weak var confirmButton: UIButton!
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@IBOutlet weak var transactionTableView: UITableView!
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```
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### ❌ Bad Naming
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```swift
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// Classes - Too abbreviated or generic
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class PayVC: UIViewController { } // What is "Pay"?
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class RefReqVM { } // Too abbreviated
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class Manager { } // Too generic
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// Variables - Unclear or abbreviated
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let amt = BehaviorRelay<String>(value: "") // What is "amt"?
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let flag = BehaviorRelay<Bool>(value: false) // Meaningless
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let data = BehaviorRelay<[Any]>(value: []) // Too generic
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// Functions - Vague
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func doSomething() { } // What does it do?
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func process() { } // Process what?
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func handle() { } // Handle what?
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// IBOutlets - Missing type suffix
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@IBOutlet weak var amount: UITextField! // Should be amountTextField
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@IBOutlet weak var btn: UIButton! // Should be confirmButton
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```
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---
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## 2. RxSwift Pattern Examples
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### ✅ Proper RxSwift Usage
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```swift
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class PaymentViewModel: BaseViewModel<PaymentState> {
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private let paymentUC: PaymentUseCase
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private let disposeBag = DisposeBag()
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let paymentAmount = BehaviorRelay<String>(value: "")
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let isProcessing = BehaviorRelay<Bool>(value: false)
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init(paymentUC: PaymentUseCase) {
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self.paymentUC = paymentUC
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super.init()
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}
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func processPayment() {
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guard !paymentAmount.value.isEmpty else {
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setState(.showError(PaymentError.invalidAmount))
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return
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}
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isProcessing.accept(true)
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paymentUC.execute(amount: paymentAmount.value)
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.subscribeOn(ConcurrentScheduler.background)
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.observeOn(MainScheduler.instance)
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.subscribe(
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onNext: { [weak self] result in
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self?.handleSuccess(result)
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},
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onError: { [weak self] error in
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self?.handleError(error)
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},
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onCompleted: { [weak self] in
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self?.isProcessing.accept(false)
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}
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)
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.disposed(by: disposeBag) // ✓ Proper disposal
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}
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}
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```
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### ❌ Common RxSwift Mistakes
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```swift
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class PaymentViewModel: BaseViewModel<PaymentState> {
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// ❌ Missing DisposeBag property
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func processPayment() {
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// ❌ MEMORY LEAK: No disposal
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paymentUC.execute(amount: paymentAmount.value)
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.subscribe(onNext: { result in
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// ❌ RETAIN CYCLE: Strong self reference
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self.handleSuccess(result)
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})
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// MISSING: .disposed(by: disposeBag)
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}
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func loadData() {
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// ❌ Wrong scheduler for UI updates
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networkService.fetchData()
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.subscribeOn(MainScheduler.instance) // Wrong!
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.subscribe(onNext: { data in
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self.tableView.reloadData() // May be on background thread
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})
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.disposed(by: disposeBag)
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}
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func refreshData() {
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// ❌ No error handling
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dataSource.getData()
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.subscribe(onNext: { data in
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// Handle data
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})
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// MISSING: onError handler
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.disposed(by: disposeBag)
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}
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}
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```
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### DisposeBag Anti-Patterns
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```swift
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// ❌ BAD: Local DisposeBag
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func loadData() {
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let disposeBag = DisposeBag() // Local variable!
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api.fetchData()
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.subscribe(onNext: { data in
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// Handle data
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})
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.disposed(by: disposeBag)
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// DisposeBag deallocates here, cancels subscription immediately!
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}
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// ❌ BAD: Multiple DisposeBags
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class ViewModel {
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private var searchDisposeBag = DisposeBag() // Anti-pattern
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private var dataDisposeBag = DisposeBag() // Anti-pattern
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}
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// ✅ GOOD: Single DisposeBag property
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class ViewModel {
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private let disposeBag = DisposeBag() // Correct!
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}
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```
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---
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## 3. Clean Architecture Examples
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### ✅ Proper Layer Separation
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```swift
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// PRESENTATION LAYER - ViewModel
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class PaymentViewModel: BaseViewModel<PaymentState> {
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private let paymentUC: PaymentUseCase // ✓ Uses UseCase
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init(paymentUC: PaymentUseCase) {
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self.paymentUC = paymentUC
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super.init()
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}
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func processPayment(amount: String) {
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paymentUC.execute(amount: amount) // ✓ Delegates to UseCase
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.subscribe(
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onNext: { [weak self] result in
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self?.setState(.success(result))
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},
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onError: { [weak self] error in
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self?.setState(.error(error))
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}
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)
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.disposed(by: disposeBag)
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}
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}
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// DOMAIN LAYER - UseCase
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protocol PaymentUseCase {
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func execute(amount: String) -> Single<PaymentResult>
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}
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class PaymentUseCaseImpl: PaymentUseCase {
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private let paymentRepository: PaymentRepository
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private let validationService: ValidationService
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init(paymentRepository: PaymentRepository,
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validationService: ValidationService) {
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self.paymentRepository = paymentRepository
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self.validationService = validationService
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}
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func execute(amount: String) -> Single<PaymentResult> {
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// ✓ Business logic in UseCase
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return validationService.validateAmount(amount)
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.flatMap { validAmount in
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return self.paymentRepository.processPayment(amount: validAmount)
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}
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}
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}
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// DATA LAYER - Repository
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protocol PaymentRepository {
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func processPayment(amount: Double) -> Single<PaymentResult>
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}
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class PaymentRepositoryImpl: PaymentRepository {
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private let apiService: PaymentApiService
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private let localStorage: PaymentLocalStorage
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func processPayment(amount: Double) -> Single<PaymentResult> {
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return apiService.processPayment(amount: amount)
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.do(onSuccess: { [weak self] result in
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self?.localStorage.savePaymentRecord(result)
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})
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}
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}
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```
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### ❌ Layer Violations
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```swift
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// ❌ BAD: ViewModel bypassing UseCase
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class PaymentViewModel: BaseViewModel<PaymentState> {
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private let apiService: PaymentApiService // ❌ Wrong layer!
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func processPayment() {
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// ❌ Direct API call, no business logic
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apiService.processPayment(amount: amount)
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.subscribe(onNext: { result in
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// ❌ Direct storage access
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RealmManager.shared.save(result)
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})
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.disposed(by: disposeBag)
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}
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}
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// ❌ BAD: Business logic in ViewModel
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class PaymentViewModel: BaseViewModel<PaymentState> {
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func processPayment(amount: Double) {
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// ❌ Validation logic in ViewModel
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guard amount > 1000 else { return }
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guard amount < 50_000_000 else { return }
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// ❌ Business rules in ViewModel
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let fee = amount * 0.01
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let total = amount + fee
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// This should all be in UseCase!
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}
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}
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// ❌ BAD: Direct instantiation
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class PaymentViewController: UIViewController {
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// ❌ Hard-coded dependencies
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private let viewModel = PaymentViewModel(
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paymentUC: PaymentUseCaseImpl() // ❌ Direct instantiation
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)
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}
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```
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---
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## 4. Security Examples
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### ✅ Secure Payment Handling
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```swift
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class PaymentSecurityManager {
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private let keychain = KeychainWrapper.standard
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// ✓ Store in Keychain
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func storePaymentToken(_ token: String, for merchantId: String) {
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let key = "payment_token_\(merchantId)"
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keychain.set(token, forKey: key,
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withAccessibility: .whenUnlockedThisDeviceOnly)
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}
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func retrievePaymentToken(for merchantId: String) -> String? {
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let key = "payment_token_\(merchantId)"
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return keychain.string(forKey: key)
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}
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}
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// ✓ Mask sensitive data in logs
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class PaymentRequest {
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let amount: Double
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let merchantId: String
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override var description: String {
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return "PaymentRequest(amount: \(amount), merchantId: ***)"
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}
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}
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// ✓ HTTPS with certificate pinning
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class PaymentNetworkManager {
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private lazy var session: URLSession = {
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let config = URLSessionConfiguration.default
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return URLSession(
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configuration: config,
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delegate: CertificatePinningDelegate(),
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delegateQueue: nil
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)
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}()
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}
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```
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### ❌ Security Violations
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```swift
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// ❌ BAD: Insecure storage
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class PaymentManager {
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func storePaymentToken(_ token: String) {
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// ❌ UserDefaults is not secure!
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UserDefaults.standard.set(token, forKey: "payment_token")
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}
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func processPayment(_ request: PaymentRequest) {
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// ❌ Logging sensitive data!
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print("Processing payment: \(request)")
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print("Card number: \(request.cardNumber)")
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}
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}
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// ❌ BAD: No certificate pinning
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class PaymentNetworkManager {
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func processPayment(_ request: PaymentRequest) {
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let url = URL(string: "http://api.payoo.vn/payment")! // ❌ HTTP!
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// ❌ No encryption
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let data = try! JSONEncoder().encode(request)
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// ❌ No certificate pinning
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URLSession.shared.dataTask(with: url) { _, _, _ in }
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}
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}
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```
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---
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## 5. UI/UX Examples
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### ✅ Proper Navigation Setup
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```swift
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// ✓ Simple title
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class PaymentViewController: UIViewController {
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override func viewDidLoad() {
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super.viewDidLoad()
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title = "Payment" // ✓ Use title property
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}
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}
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// ✓ Title with subtitle (only when subtitle exists)
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class StoreSelectionViewController: UIViewController {
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private let titleDescription: String?
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override func viewDidLoad() {
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super.viewDidLoad()
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if let description = titleDescription, !description.isEmpty {
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// ✓ Only use titleView when subtitle exists
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navigationItem.titleView = createTitleView(
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title: "Store Selection",
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description: description
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)
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} else {
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// ✓ Use simple title when no subtitle
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title = "Store Selection"
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}
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}
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}
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// ✓ Loading states with feedback
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class QRSaleViewController: UIViewController {
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private func bindLoadingStates() {
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viewModel.isProcessing
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.bind(to: loadingIndicator.rx.isAnimating)
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.disposed(by: disposeBag)
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viewModel.isProcessing
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.map { !$0 }
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.bind(to: processButton.rx.isEnabled)
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.disposed(by: disposeBag)
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viewModel.isProcessing
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.map { $0 ? "Processing..." : "Process Payment" }
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.bind(to: processButton.rx.title(for: .normal))
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.disposed(by: disposeBag)
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}
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}
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// ✓ Accessibility
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class PaymentAmountView: UIView {
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private func setupAccessibility() {
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amountTextField.isAccessibilityElement = true
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amountTextField.accessibilityLabel = "Payment amount"
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amountTextField.accessibilityHint = "Enter the payment amount in VND"
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// ✓ Dynamic Type support
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amountTextField.font = UIFont.preferredFont(forTextStyle: .title2)
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amountTextField.adjustsFontForContentSizeCategory = true
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}
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}
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```
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### ❌ UI/UX Issues
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```swift
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// ❌ BAD: Using titleView for simple title
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class PaymentViewController: UIViewController {
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override func viewDidLoad() {
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super.viewDidLoad()
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// ❌ Unnecessary custom title view
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let titleLabel = UILabel()
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titleLabel.text = "Payment"
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navigationItem.titleView = titleLabel // Should use title property!
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}
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}
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// ❌ BAD: No loading feedback
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class QRSaleViewController: UIViewController {
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private func processPayment() {
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// ❌ No loading indicator
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viewModel.processPayment() // User has no feedback!
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}
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}
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// ❌ BAD: No accessibility
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class PaymentAmountView: UIView {
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// ❌ No accessibility setup
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// ❌ No Dynamic Type support
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// ❌ Missing accessibility labels
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}
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```
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---
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## 6. Performance Examples
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### ✅ Proper Memory Management
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```swift
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class ImageDownloadManager {
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private let cache = NSCache<NSString, UIImage>()
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private var activeDownloads: [String: Disposable] = [:]
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func downloadImage(from url: String) -> Observable<UIImage> {
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let cacheKey = url as NSString
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// ✓ Check cache first
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if let cachedImage = cache.object(forKey: cacheKey) {
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return .just(cachedImage)
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}
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// ✓ Cancel existing download
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activeDownloads[url]?.dispose()
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let download = URLSession.shared.rx
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.data(request: URLRequest(url: URL(string: url)!))
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.compactMap { UIImage(data: $0) }
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.do(
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onNext: { [weak self] image in
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self?.cache.setObject(image, forKey: cacheKey)
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},
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onDispose: { [weak self] in
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self?.activeDownloads.removeValue(forKey: url)
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}
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)
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.share(replay: 1, scope: .whileConnected)
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activeDownloads[url] = download.connect()
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return download
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}
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}
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// ✓ Database on background thread
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class TransactionRepository {
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func getTransactions() -> Observable<[Transaction]> {
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return Observable.collection(from: realm.objects(TransactionObject.self))
|
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.map { results in
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return results.map { Transaction(from: $0) }
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}
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.subscribeOn(ConcurrentScheduler.background) // ✓ Background
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.observeOn(MainScheduler.instance) // ✓ Main for UI
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}
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}
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```
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|
||||
### ❌ Performance Issues
|
||||
|
||||
```swift
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// ❌ BAD: Memory leak from strong references
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class ImageDownloadManager {
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private var downloads: [URLSessionDataTask] = [] // ❌ Strong references
|
||||
|
||||
func downloadImage(from url: String) -> Observable<UIImage> {
|
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return Observable.create { observer in
|
||||
let task = URLSession.shared.dataTask(with: URL(string: url)!) { data, _, _ in
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||||
// Process
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||||
}
|
||||
|
||||
self.downloads.append(task) // ❌ Never removed - leak!
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task.resume()
|
||||
|
||||
return Disposables.create {
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||||
task.cancel()
|
||||
// ❌ Still in downloads array!
|
||||
}
|
||||
}
|
||||
}
|
||||
}
|
||||
|
||||
// ❌ BAD: Blocking main thread
|
||||
class TransactionRepository {
|
||||
func getTransactions() -> Observable<[Transaction]> {
|
||||
return Observable.create { observer in
|
||||
// ❌ Blocking operation on main thread!
|
||||
let realm = try! Realm()
|
||||
let results = realm.objects(TransactionObject.self)
|
||||
let transactions = results.map { Transaction(from: $0) }
|
||||
|
||||
observer.onNext(Array(transactions))
|
||||
observer.onCompleted()
|
||||
|
||||
return Disposables.create()
|
||||
}
|
||||
}
|
||||
}
|
||||
```
|
||||
|
||||
---
|
||||
|
||||
## Common Review Scenarios
|
||||
|
||||
### Scenario 1: New Feature Review
|
||||
|
||||
**Code**: New payment processing feature
|
||||
|
||||
**Check**:
|
||||
1. Naming: All classes/variables descriptive?
|
||||
2. RxSwift: Disposal and memory management?
|
||||
3. Architecture: Proper layer separation?
|
||||
4. Security: Payment data handled securely?
|
||||
5. Tests: Unit tests included?
|
||||
6. Performance: No blocking operations?
|
||||
|
||||
### Scenario 2: Bug Fix Review
|
||||
|
||||
**Code**: Fix for crash in transaction list
|
||||
|
||||
**Check**:
|
||||
1. Root cause addressed?
|
||||
2. No force unwrapping?
|
||||
3. Proper error handling added?
|
||||
4. Tests for the bug scenario?
|
||||
5. No new issues introduced?
|
||||
|
||||
### Scenario 3: Refactoring Review
|
||||
|
||||
**Code**: Refactor ViewModel to use Clean Architecture
|
||||
|
||||
**Check**:
|
||||
1. UseCase layer added?
|
||||
2. Business logic moved from ViewModel?
|
||||
3. DI setup correctly?
|
||||
4. Tests still pass?
|
||||
5. No breaking changes?
|
||||
|
||||
---
|
||||
|
||||
**Detailed Examples**: See `examples.md` for extensive code samples and scenarios.
|
||||
|
||||
## Quick Reference Checklist
|
||||
|
||||
Copy this for quick reviews:
|
||||
|
||||
```markdown
|
||||
## Review Checklist
|
||||
|
||||
### Naming ✅
|
||||
- [ ] Classes: PascalCase, descriptive
|
||||
- [ ] Variables: camelCase, meaningful
|
||||
- [ ] Booleans: is/has/should/can prefix
|
||||
- [ ] No abbreviations
|
||||
- [ ] IBOutlets: type suffix
|
||||
|
||||
### RxSwift 🔄
|
||||
- [ ] All subscriptions disposed
|
||||
- [ ] [weak self] in closures
|
||||
- [ ] Correct schedulers
|
||||
- [ ] Error handling present
|
||||
- [ ] Using BehaviorRelay
|
||||
|
||||
### Architecture 🏗️
|
||||
- [ ] ViewModel → UseCase → Repository
|
||||
- [ ] No business logic in ViewModel
|
||||
- [ ] Dependencies injected
|
||||
- [ ] BaseViewModel extended
|
||||
- [ ] Repository pattern used
|
||||
|
||||
### Security 🔒
|
||||
- [ ] Payment data in Keychain
|
||||
- [ ] No sensitive logs
|
||||
- [ ] HTTPS with pinning
|
||||
- [ ] Input validation
|
||||
|
||||
### UI/UX 🎨
|
||||
- [ ] title for simple titles
|
||||
- [ ] titleView only with subtitle
|
||||
- [ ] Accessibility configured
|
||||
- [ ] Loading states shown
|
||||
|
||||
### Performance ⚡
|
||||
- [ ] DB on background thread
|
||||
- [ ] No retain cycles
|
||||
- [ ] Image caching
|
||||
- [ ] Memory management proper
|
||||
```
|
||||
Reference in New Issue
Block a user