SwiftUI interview questions

SwiftUI vs UIKit rendering

How is the way SwiftUI draws the screen fundamentally different from UIKit?

#swiftui #uikit #declarative #rendering

@State and @Binding

You're building a SwiftUI settings screen. A child view SettingsRow with a toggle needs to read and change an isOn value the parent owns. Which property…

#state #binding #data-flow #source-of-truth

Diagnosing @State updates

A junior asks you why the screen doesn't update after they change a @State value in SwiftUI. Start by explaining what @State is.

#state #update #debugging #observable

App entry point

In a SwiftUI app, what does @main mean?

#main #app-protocol #scene #windowgroup

Presenting a sheet

In a SwiftUI list, tapping an item should present that item's detail in a sheet. With many items, what's the most appropriate approach?

#sheet #modal #presentation #item

NavigationStack navigation

How do you implement navigation between screens in SwiftUI?

#navigationstack #navigationpath #navigationlink #deep-link

SwiftUIMultiple choiceIntroPayPal

Modifier order

This is an interview where we look at SwiftUI code together and fix it. Which statement about the rendered result of these two lines is correct? …

#modifier #background #padding #modifier-order

SwiftUIMultiple choiceIntroFidelity Investments

Choosing property wrappers

Select all the correctly matched pairs of situation and SwiftUI property wrapper. (Assume iOS 16 and ObservableObject.)

#state #stateobject #observedobject #environmentobject

View as a struct

UIView is a class, so why was SwiftUI's View designed as a struct?

#view #struct #value-type #protocol

@StateObject vs @ObservedObject

In this SwiftUI view, ItemListView's data resets every time the parent view is re-evaluated. What's the cause, and what's the right fix? …

#stateobject #observedobject #observableobject #lifetime

Observation migration

You're moving a SwiftUI app's ObservableObject code to @Observable. Select all the correct migrations.

#observable #migration #bindable #environment

Data flow design

Using the single source of truth principle in SwiftUI, how do you decide which view should own a given piece of state?

#data-flow #source-of-truth #binding #environment

Environment injection

In a SwiftUI app you injected .environment(session) at an intermediate view (HomeView) as shown below. ProfileView, which uses @Environment(Session.self) var…

#environment #environmentobject #injection #crash

SwiftUI view lifecycle

SwiftUI views have no viewDidLoad or viewWillAppear like UIKit. How does a view actually get created, appear, update, and disappear? Center your answer on how…

#lifecycle #onappear #task #body

Embedding SwiftUI in UIKit

How do you put a SwiftUI screen into a UIKit app?

#uiviewrepresentable #uihostingcontroller #interop #coordinator

UIViewRepresentable behavior

Select all the correct statements about SwiftUI's UIViewRepresentable.

#uiviewrepresentable #coordinator #updateuiview #interop

Stack and Spacer layout

Select all the correct statements about the layout result of this SwiftUI view. …

#hstack #spacer #frame #maxwidth

Reusable component design

You're building a design system's card component in SwiftUI to reuse across many screens. When would you use each approach (a custom View, a ViewModifier, a…

#viewmodifier #reusable #viewbuilder #style

@Published and view updates

Select all the correct statements about how ObservableObject's @Published updates SwiftUI views.

#published #observableobject #objectwillchange #combine

SwiftUIMultiple choiceBasicsCapital One

onChange vs onReceive

Select all the correct statements about SwiftUI's onChange(of:) and onReceive(_:).

#onchange #onreceive #combine #modifier

SwiftUIShort answerBasicsSamsung Electronics

List scrolling diagnosis

You got a report that a SwiftUI List stutters while scrolling, and that row toggles and images change to the wrong ones or flicker. In what order do you…

#list #lazyvstack #identifiable #performance

SwiftUIMultiple choiceBasicsSamsung Electronics

Form validation state design

This is SwiftUI live coding. A sign-up screen has four fields (name, ID, password, password confirmation) and a submit button. If name or ID is empty, show a…

#form #validation #alert #state

SwiftUIShort answerBasicsSwiggy

UIKit to SwiftUI migration

You want to move a service app built in UIKit over to SwiftUI. What strategy do you use to introduce it?

#migration #uihostingcontroller #navigation #interop

SwiftUIShort answerBasicsZomato

State-driven view switch

This is a 15-minute SwiftUI live coding exercise. Tapping an "Add" button should show a quantity stepper (minus/plus) in the same spot, and when the quantity…

#state #conditional-view #stepper #animation

SwiftUIShort answerBasicsRobinhood

Swift Charts implementation

This is on-site coding. For a stock app, how would you build a Chart in Swift Charts that draws the last 30 days of closing prices as a line, with axes, range…

#swift-charts #chart #linemark #visualization

SwiftUIShort answerBasicsAlibaba Group

WidgetKit and SwiftUI

You've been assigned home screen widget development. Why can widgets only be built with SwiftUI and not UIKit?

#widgetkit #widget #timeline #appintent

SwiftUIShort answerBasicsMercari

SwiftUI state ownership

In a SwiftUI product editing screen, the parent view owns the product model and a child view edits just the price field. Among @State, @Binding, and…

#swiftui #state #binding #observation

SwiftUIShort answerBasicsHSBCunverified source

Choosing SwiftUI or UIKit

You're adding a new account detail screen to a banking app built in UIKit. By what criteria would you decide whether to build this screen in SwiftUI or UIKit?

#swiftui #uikit #integration #hosting-controller

SwiftUIShort answerBasicsPelotonunverified source

Single state tally screen

A counter screen built in SwiftUI has increment, decrement, and reset buttons plus a display of the current value. How would you arrange the state so the…

#swiftui #state #counter #single-source

SwiftUIShort answerBasicsExpediaunverified source

SwiftUI API loading state

A SwiftUI list screen loads data from a hotel API. To handle loading, success, no results, and error on screen without missing one, how would you model the…

#swiftui #task #loading-state #api

SwiftUIShort answerBasicsYogiyounverified source

SwiftUI async MainActor state

A SwiftUI order list ViewModel calls an async API and then changes the screen state with the result. Under Swift 6 strict concurrency, which part of this…

#swiftui #mainactor #async-await #error-state

SwiftUIShort answerBasicsBithumbunverified source

List item identity

In a SwiftUI List showing live prices, every price update makes rows flicker and reappear and the scroll position jumps. How should you define the model's…

#swiftui #list #identity #realtime

SwiftUIShort answerBasics중고나라unverified source

Unidirectional state flow

A used-goods listing screen built in SwiftUI has input fields, validation, submission, and error display all tangled together. If you reorganized it as a…

#swiftui #unidirectional #state #validation

Observation framework

In SwiftUI, what does the iOS 17 @Observable macro give you over the older ObservableObject plus @Published approach? Ground it in how the two work internally.

#observable #observation #observableobject #published

View identity

In the code below, toggling isCompact wipes whatever was typed in the text field. Can you explain why using SwiftUI's concept of identity? …

#identity #structural-identity #explicit-identity #id

ForEach identifiers

In this SwiftUI to-do list, inserting an item at the front makes every row flicker instead of animating the insertion, and each row's toggle state shifts down…

#foreach #identifiable #id #list

SwiftUI layout algorithm

Can you walk me through the three steps that determine a SwiftUI layout?

#layout #proposal #size #frame

MVVM in SwiftUI

If you apply MVVM to a screen in a SwiftUI app that supports iOS 17 and later, how do you define the ViewModel and how does the view own it?

#mvvm #viewmodel #observable #mainactor

.task vs onAppear

In a SwiftUI view that loads data, what's the correct statement about how these two pieces of code behave differently? …

#task #onappear #cancellation #async

SwiftData and SwiftUI

For a new SwiftUI app's local storage you picked SwiftData over Core Data. How does SwiftData integrate with SwiftUI?

#swiftdata #coredata #query #modelcontainer

SwiftUIShort answerAdvancedCapital One

switchToLatest search pipeline

You're building a Combine pipeline for a SwiftUI search screen that calls the API as the user types. What's the difference between putting switchToLatest()…

#combine #switchtolatest #flatmap #debounce

SwiftUIShort answerAdvancedCapital One

Combine list-detail live coding

This is a 20-minute live coding exercise. Using only Combine, build a two-screen SwiftUI app that fetches a list from an API, shows it, and navigates to a…

#combine #live-coding #navigationstack #observableobject

SwiftUIShort answerAdvancedKREAM

@Observable ownership and passing

When working with an iOS 17 @Observable class in SwiftUI views, using "who owns it" and "how is it passed" as the criteria, when do you use @State, a plain…

#observation #observable #state #bindable

SwiftUIShort answerAdvancedHuray Positive

Search tab design

This is a take-home assignment. Build the App Store "Search" tab in SwiftUI using the iTunes Search API. You need recent search terms (stored locally), a…

#searchable #task-id #debounce #recent-searches

SwiftUIShort answerAdvancedNaver Webtoon

Observation dependency tracking

In iOS 17 SwiftUI, when one property on an @Observable model changes, only some of the views using that model redraw, not all of them. What does SwiftUI use to…

#observation #observable #swiftui #ios17

SwiftUI performance diagnosis

On a dashboard screen built in SwiftUI, the whole screen stutters on every character typed into a text field. What's your hypothesis for what's going on?

#performance #body #printchanges #instruments

SwiftUIShort answerExpertPayPalunverified source

Finding SwiftUI defects

This is a SwiftUI live coding review. Find as many defects as you can in the feed screen code below, and for each one say why it's a problem and how you'd fix…

#debugging #code-review #observedobject #foreach

Observation tracking granularity

In this SwiftUI plus Observation code, when only store.count is incremented, select all the views whose body is re-evaluated. …

#observable #observation #tracking #body

Large list performance

A SwiftUI feed showing thousands of items stutters while scrolling. Based on the internal differences between List and ScrollView + LazyVStack, which do you…

#list #lazyvstack #performance #anyview