Interview round · every platform

Swift and SwiftUI interview prep

The Swift and SwiftUI part of an iOS loop is where the technical screen lives. It is scored less on definitions than on whether you can explain a real bug: the actor that was not isolated the way you said, the view that re-rendered because of where the state lived.

For: iOS engineers preparing the technical screen or the language and UI rounds of a loop.

Mike Salari · Staff mobile engineer · 500+ technical interviews from the hiring side

Read the 8 guides Build my prep plan

What the round scores

Part of the round	What the interviewer writes down
Swift language	Value and reference semantics, protocols and generics, explained from code you wrote.
Concurrency	Isolation, Sendable and cancellation, and what runs on the main actor.
Memory	ARC, retain cycles and how you found one in a real app.
SwiftUI state and identity	Who owns the state, what triggers a body evaluation, and why identity matters in a list.
UIKit	When you would still reach for it, and how the two frameworks live together in one app.

Loops differ by company. This is the common shape of the round in senior mobile loops, not a promise about any one employer.

A weak answer and a strong one

Weak

Recites the definition of @MainActor.

Strong

Explains that isolation applies to the function, not to the work it awaits, using a network call as the example.

Weak

"@StateObject owns it, @ObservedObject does not."

Strong

Shows the bug that appears when the owner is wrong, and how it was noticed.

When the iOS loop is days away, you do not need a curriculum, you need triage. This book is for senior iOS engineers who want to rehearse the senior iOS interview questions that come up most, out loud, with the push an interviewer makes next and a way back when an answer goes wrong. With several weeks, read the full interview map first.

The second question

Follow-ups that decide the round

“You said the view model is @MainActor. What happens to the network call inside it?”

Tests whether you understand isolation beyond the annotation.

“The list stutters on an older iPhone. Where do you look first?”

Tests whether you measure before you change anything.

“Why is this view body evaluated on every keystroke?”

Tests state ownership and identity, not framework trivia.

How to prepare for it

Start with the technical interview map
Which rounds exist and what each one scores.
Swift, then SwiftUI, then UIKit
Answer each guide's questions out loud before reading the answer.
Prepare one real bug per area
Concurrency, memory, state: one story each, with how you found it.

Guides for this round

iOS · 18 min

iOS interview questions in 2026, round by round

iOS interview questions for 2026, organised by round: Swift, concurrency, memory, SwiftUI, UIKit, architecture, system design, testing, coding and behavioural.

iOS · 14 min

iOS technical interview: the rounds and what each scores

What an iOS technical interview loop contains, what each round scores, and where strong Swift candidates still lose it.

iOS · 13 min

Swift interview questions and answers, as they are scored

Swift interview questions with spoken answers: value and reference types, protocols, generics, memory and errors, and the follow-up each one leads to.

iOS · 13 min

SwiftUI interview questions and what they score

SwiftUI interview questions on identity, state ownership, Observation and performance, each with the answer that scores, the trap and the follow-up.

iOS · 12 min

UIKit interview questions still asked in 2026

UIKit interview questions that still appear in iOS loops: lifecycle, layout passes, cell reuse, diffable data sources, and UIKit with SwiftUI.

Books and practice

For intermediate and senior iOS engineers whose SwiftUI works until real load arrives: cancellation, backgrounding, ownership pressure. It is the production depth behind the SwiftUI interview questions about state, identity and performance, taught through failure labs rather than component recipes. It is not a first SwiftUI book.

For iOS and Android, Interview Runtime is the practice layer: interview answer practice where you speak first and the follow-up comes after, the way a real round runs. It is for engineers who have read enough and now need to hear where their own answer breaks. The free iOS sample shows how it works before you buy.

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