Architecture interview questions

Cocoa MVC

How does Cocoa MVC in UIKit differ from the textbook MVC?

#mvc #cocoa-mvc #massive-view-controller #uikit

Placing MVC roles

In an MVC iOS app, where's the best place for the code that turns a date string from the server into a display format for the user's locale?

#mvc #responsibility #layering

Singleton pattern

When do you use a singleton in an iOS app, and what's the problem with it?

#singleton #global-state #testing #thread-safety

Delegate pattern

Can you explain the Delegate pattern that shows up all over UIKit?

#delegate #notification #kvo #closure

Choosing a communication style

In which of these situations is NotificationCenter the best fit?

#delegate #notification #closure #design

ArchitectureShort answerIntroExpedia

Scope of a singleton

In a travel app, a global SessionManager.shared holds auth, cache, analytics, and experiment values all at once, and that makes testing hard. How would you dec…

#singleton #dependency-injection #testability #global-state

MVC vs MVVM

Someone proposes moving an app that works fine on MVC over to MVVM. What's the fundamental difference between MVVM and MVC?

#mvc #mvvm #viewmodel #testability

ViewModel boundaries

In MVVM, which of these should a ViewModel not have? Select all that apply.

#mvvm #viewmodel #responsibility #uikit

MVP, VIPER, MVI, RIBs

Besides MVVM, walk me through the architectures you know (MVP, VIPER, MVI, RIBs, and so on), one at a time, and tell me how they differ.

#mvp #viper #mvi #ribs

Dependency injection

Why do we do dependency injection in an iOS app?

#dependency-injection #protocol #testing #composition-root

Choosing DI style

Which of these statements about dependency injection styles are correct? Select all that apply.

#dependency-injection #initializer #property #environment

How KVO works

How does KVO in the Objective-C runtime detect property changes under the hood?

#kvo #kvc #objective-c-runtime #isa-swizzling

NotificationCenter behavior

Which of these statements about Foundation's NotificationCenter are correct? Select all that apply.

#notification #notificationcenter #thread #observer

SOLID principles

Can you explain the five SOLID principles with iOS code examples, not shapes and animals?

#solid #srp #ocp #lsp

Identifying design patterns

Which of these correctly pair a situation with a design pattern? Select all that apply.

#design-pattern #observer #adapter #decorator

Reactive programming

What problems does reactive programming, as in RxSwift or Combine, solve for you on iOS?

#rxswift #combine #reactive #async-sequence

ArchitectureShort answerBasicsWalmart

DI vs DIP

Dependency Injection and the Dependency Inversion Principle have similar names. What's the difference?

#dependency-injection #dependency-inversion #solid #protocol

ArchitectureMultiple choiceBasicsWalmart

Unit testing with singletons

In a codebase where a singleton like AnalyticsManager.shared is referenced directly all over, you want to unit test a view model that uses it. Which approaches…

#singleton #unit-test #testability #mock

ArchitectureShort answerBasicsGojek

Judging third-party libraries

This is a take-home review. You didn't use a single third-party library in the app you submitted, and the interviewer asks why not, and if you had to, which pa…

#third-party #dependency #spm #adapter

ArchitectureMultiple choiceBasicsPaytm

Singleton deinit

For a singleton of the form static let shared = SessionManager(), someone asks "can you make deinit get called, and is there a real case where you'd need to?" …

#singleton #deinit #lifetime #scope

ArchitectureShort answerBasicsCRED

Where business logic lives

Pick the last screen you built and walk me through it end to end. Where did you put the business logic on that screen, and why?

#mvvm #business-logic #viewmodel #domain

ArchitectureShort answerBasicsDropboxinterview report

Modularizing a file list feature

You're designing an iOS file and folder list feature with search and pull-to-refresh. To keep it maintainable independent of the UI framework, what module boun…

#feature-module #repository #search #refresh

Coordinator pattern

What problem is the Coordinator in MVVM-C meant to solve?

#coordinator #navigation #mvvm-c #routing

Coordinator memory

In this Coordinator implementation, LoginCoordinator stays in memory after the login flow finishes. Which is the most likely cause? …

#coordinator #memory #retain-cycle #weak

ArchitectureShort answerAdvancedPayPalinterview report

Minimal NotificationCenter

This is a live coding exercise. Without Foundation's NotificationCenter, design and implement a small EventBus in Swift that subscribes and publishes by name. …

#pub-sub #observer #notification #coding

Legacy MVC to MVVM

You've been asked to move a 5-year-old MVC app (150 view controllers, almost no tests) to MVVM, and the service has to keep shipping. What's your strategy?

#migration #legacy #mvvm #refactoring

API client abstraction

You have three network clients for the auth server, product server, and payment server that are similar but slightly different (different headers, encoding, er…

#protocol #generic #network-layer #endpoint

ArchitectureShort answerAdvancedAirbnbinterview report

Modularization strategy

You want to split an app that grew into a single target into modules. What criteria do you use to draw module boundaries?

#modularization #spm #framework #build-time

Module dependency direction

The SearchFeature module needs to open CheckoutFeature's payment screen from a search result. What's the correct way to do this without creating a circular dep…

#modularization #dependency #interface #circular

Deciding on TCA

Your team is evaluating TCA (The Composable Architecture). What problems does TCA solve?

#tca #composable-architecture #unidirectional #reducer

TCA components

In TCA, you're implementing "tap a button, fetch a list over the network, show it on screen." Which description of a component's role is wrong?

#tca #reducer #effect #state

ArchitectureShort answerAdvancedHeadspace

Analytics event dispatch

This is a take-home assignment. Design a layer in plain Swift that sends analytics events to several services (Google Analytics, Snowplow, and so on). Requirem…

#analytics #protocol #dispatcher #open-closed

ArchitectureShort answerAdvancedMicrosoft

Data layer for a tabbed app

This is a whiteboard design. You're building a stripped-down Outlook app with only a Messages tab and a Contacts tab. Data read from the API has to show up in …

#repository #single-source-of-truth #caching #startup

ArchitectureShort answerAdvancedCRED

Limits of MVVM

You said you chose MVVM for this feature. When does MVVM actually hurt?

#mvvm #trade-off #refactoring #strangler

ArchitectureMultiple choiceAdvancedFlipkart

Deep links at scale

In a large app split into dozens of modules, which of these are correct designs for handling deep links (URL schemes, Universal Links, push payloads)? Select a…

#deep-link #universal-link #router #modularization

ArchitectureShort answerAdvancedDiDi

Request state machine

A screen with a network request has loading, success, failure, retry, refresh, and cancel states all tangled together. How do you design those state transition…

#state-machine #enum #loading-state #cancellation

ArchitectureShort answerAdvancedKuaishou

Extensible search API

Here's a file search function. Now it has to find only "UTF-8 txt or H.264 mp4" and "files modified within the last week," and the conditions will keep growing…

#api-design #closure #predicate #open-closed

ArchitectureShort answerAdvanced네이버웹툰

Clean Architecture circles vs user flow

Your tech lead says "the Clean Architecture circles (the concentric diagram) don't seem to match the user's perspective in iOS development." The flow the user …

#clean-architecture #dependency-rule #use-case #user-flow

ArchitectureShort answerAdvanced당근interview report

Server Driven UI

You want to change the feed screen's section makeup, order, and card types without shipping an app update. How do you design the Server Driven UI schema and th…

#server-driven-ui #sdui #component-registry #versioning

ArchitectureShort answerAdvanced당근

Designing for long-term maintenance

You've been asked "how would you design this feature so it's still maintainable years from now?" Using a feature you built recently as the example, explain wha…

#maintainability #design-decision #testability #adr

ArchitectureShort answerAdvancedInstacartinterview report

Reusable UI component boundaries

On a UIKit cart screen, the product card is used in the list, in search, and in recommendations, but the tap behavior and badges differ per screen. When you de…

#uikit #reusable-component #collection-view #configuration

ArchitectureShort answerAdvancedJD.com

Moving from MVC to MVVM

In an existing UIKit shopping app, the UIViewController handles the API calls, the cache, and the loading UI. When you move from MVC to MVVM, which layer would…

#mvvm #repository #migration #caching

ArchitectureShort answerAdvanced카카오모빌리티interview report

Protocol-oriented composition

In an iOS ride service feature with route guidance, fare calculation, and live location updates, the inheritance hierarchy has gotten complicated. With protoco…

#protocol-oriented #dependency-injection #composition #ios

ArchitectureShort answerAdvanced우아한형제들interview report

Incremental legacy refactoring

You need to improve the structure of a massive ViewController in a live UIKit order feature without rewriting it all at once. If you split the work into small …

#refactoring #legacy #feature-flag #migration

Architecture by team size

As an iOS team grows from 5 to 10 to 100 people, how should the way you manage code conflicts, quality, and architecture change at each stage?

#scaling #team #modularization #code-ownership

Large SwiftUI app structure

If you were designing a SwiftUI app from scratch with dozens of screens and several teams working on it, how would you set up state management, navigation, dep…

#swiftui #large-scale #modularization #navigation

Method swizzling

Which of these statements about method swizzling are correct? Select all that apply.

#method-swizzling #objective-c-runtime #aop #risk

Clean Architecture layers

When you apply Clean Architecture on iOS, can you walk me through the layers and the dependency rule?

#clean-architecture #use-case #domain #boundary