UIKit interview questions

frame vs bounds

While debugging a custom UIKit view you notice bounds.origin isn't (0, 0). What's the difference between frame and bounds?

#frame #bounds #coordinate #scrollview

View controller lifecycle

When a screen appears for the first time, which order do the UIViewController lifecycle methods run in?

#viewcontroller #lifecycle #viewdidload #viewdidappear

Auto Layout basics

How is an Auto Layout constraint represented internally, as a formula?

#autolayout #constraint #nslayoutanchor #visual-format

Safe Area

Which of the following statements about the Safe Area are correct? Pick all that apply.

#safe-area #layout-guide #notch #autolayout

Leading vs Left

When would it be appropriate to use leftAnchor instead of leadingAnchor in an Auto Layout constraint?

#autolayout #leading #rtl #localization

UIKitShort answerIntroUber

Storyboards vs code UI

Your team is debating whether to use storyboards or build UI purely in code. What are the pros and cons of each?

#storyboard #xib #programmatic-ui #git-conflict

UIKitMultiple choiceIntroZomato

UIResponder inheritance chain

Which is the correct inheritance chain from NSObject down to UIButton?

#uiresponder #uicontrol #inheritance #uibutton

viewDidLoad and network requests

A teammate kicks off a network request directly in viewDidLoad and updates the UI when the response arrives. What problems can this cause?

#viewdidload #lifecycle #network #task

Content Hugging and Compression Resistance

You've placed titleLabel and dateLabel side by side on one row with Auto Layout. When the title gets long, the title should shrink (truncate) and the date…

#autolayout #hugging #compression-resistance #priority

Intrinsic Content Size

You put a custom view you built (say, a tag chip view) into a UIStackView and it's sized to zero and invisible. How would you explain the cause and the fix in…

#autolayout #intrinsic-content-size #custom-view #invalidate

UIKitShort answerBasicsTikTok

Layout update methods

What do setNeedsLayout and layoutIfNeeded each do in UIKit, and when should you call them?

#setneedslayout #layoutifneeded #layoutsubviews #setneedsdisplay

Constraint animation

This Auto Layout code is meant to slide a panel up, but the panel jumps into place with no animation. Why? …

#autolayout #animation #layoutifneeded #constraint

Cell reuse and async images

You've inherited a UITableView feed where, on fast scrolling, images briefly show up in the wrong cell and then get replaced. What's the cause?

#tableview #collectionview #cell-reuse #async-image

dequeueReusableCell API

Which statements about UITableView's dequeueReusableCell(withIdentifier:for:) and dequeueReusableCell(withIdentifier:) are correct? Pick all that apply.

#tableview #dequeue #reuse-identifier #register

Dynamic cell height

You need a UITableView cell whose height varies with the length of a comment. What do you set up so the cell height fits its content automatically?

#tableview #self-sizing #automatic-dimension #estimated-height

UIKitShort answerBasicsTikTok

Responder chain and hit testing

When you tap the screen in a UIKit app, how does the system decide which view receives the touch (hit testing)?

#responder-chain #hit-test #touch #first-responder

View hierarchy traversal

How would you write a function that starts at a root view and finds a view matching some condition (say, tag == 99 or a specific type)? …

#view-hierarchy #bfs #dfs #subviews

Dark Mode support

Which statements about supporting Dark Mode in a UIKit app are correct? Pick all that apply.

#dark-mode #trait-collection #dynamic-color #cgcolor

UIKitShort answerBasicsGoogle

Pinning four corners with constraints

Live coding. Given an [UIImage], how would you build a custom UIView that pins one image to each of its four corners using only constraints in code? …

#autolayout #nslayoutconstraint #anchor #programmatic-ui

UIKitShort answerBasicsSwiggy

Sticky header, carousel, pull to refresh

A take-home review. The home screen needs (1) a filter header that stays pinned to the top while scrolling and (2) two rows of horizontally scrolling…

#uicollectionview #compositional-layout #sticky-header #carousel

UIKitMultiple choiceBasicsLINE

Calls before viewDidLoad

For a UIViewController instantiated from a storyboard, which methods are called before viewDidLoad()? Pick all that apply.

#lifecycle #loadview #awakefromnib #init-coder

Separating dataSource and delegate

Why did Apple design UITableView with two protocols, dataSource and delegate, instead of just letting you hand it a data array?

#uitableview #datasource #delegate #protocol

UIKitMultiple choiceBasicsTencent

Table view call order

In a UITableView that doesn't use estimatedRowHeight, what's the correct order these four methods are called in right after reloadData()? -…

#uitableview #datasource #heightforrow #estimatedrowheight

UIKitShort answerBasicsLyft

Image cell reuse and cancellation

In a UIKit collection view with image cells, fast scrolling makes the previous request's response flash on a reused cell before it changes. What would you…

#uikit #collection-view #image-loading #reuse

UIKitShort answerBasicsOracleunverified source

Finding the common UIView parent

You're writing a function that finds the nearest common parent of two UIViews. Which data structure would you keep one view's superview chain in?

#uiview #view-hierarchy #ancestor #set

UIKitShort answerBasicsBBCunverified source

List UI with a completed state

A UIKit table screen shows election results. Once every district's result has arrived, the refresh button should hide and the winner's row should be…

#uitableview #diffable-data-source #state #snapshot

UIKitShort answerBasicsThe Swingunverified source

Auto Layout priorities

On a narrow screen, a title label and a price label have to share one row, and both demand their full text width. In Auto Layout, what decides which label gets…

#autolayout #constraint-priority #hugging #compression-resistance

UIKitShort answerBasicsInstacart

Undoable game state

A tic-tac-toe game built with UIKit needs unlimited undo. What would you store to support undoing?

#state-management #undo #snapshot #uikit

UIKitShort answerBasicsJD.com

Chat input bar and keyboard layout

In a UIKit chat screen, the input bar has to sit right on top of the keyboard and follow it as it rises. How would you connect keyboard height changes to Auto…

#keyboard #autolayout #chat #safe-area

UIKitShort answerBasicsKakao Mobilityunverified source

Self-sizing cells and Dynamic Type

A UIKit car listing cell has to grow in height and not truncate under the accessibility large text settings. How do you set up the constraints so the cell…

#dynamic-type #self-sizing #uikit #accessibility

Overriding hitTest

You've put a round button in the middle of a custom UIKit tab bar that sticks 20pt up above it. Tapping the part that sticks out does nothing. Which override…

#hit-test #touch #custom-view #bounds

UIView and CALayer

How do UIView and CALayer relate to each other, and why are their roles split?

#calayer #uiview #core-animation #rendering

UIKitShort answerAdvancedAirbnbunverified source

Nested scrolling cell design

You need to put a horizontally scrolling UICollectionView inside a UITableViewCell in code (a carousel row like the App Store's Today tab). Who should own the…

#tableview #collectionview #nested #cell-reuse

UIKitShort answerAdvancedSnapunverified source

Diagnosing scroll performance

You get a report that scrolling stutters on a feed screen that mixes images and text. Where do you start, and how do you check?

#performance #scroll #instruments #hitch

Compositional Layout and Diffable Data Source

You're moving a screen built with UICollectionViewFlowLayout and an index-based dataSource to UICollectionViewCompositionalLayout and…

#collectionview #compositional-layout #diffable-datasource #snapshot

Diffable Data Source behavior

Which statements about using UICollectionViewDiffableDataSource are correct? Pick all that apply.

#diffable-datasource #snapshot #hashable #collectionview

Finding the common superview

Given several UIViews, how would you design a function that returns their nearest common superview?

#view-hierarchy #superview #lca #algorithm

UIKitShort answerAdvancedMeta

Reimplementing UIScrollView

Suppose UIScrollView didn't exist and you had to build a UIView subclass where content follows your finger. Which property would you change to move the content?

#uiscrollview #bounds #pan-gesture #contentoffset

UIKitShort answerAdvancedReddit

Cell impression tracking

Each post in a feed has to send an impression event exactly once when it has been at least 50% visible for at least 1 second. How would you design this…

#uitableview #impression #analytics #willdisplay

UIKitShort answerAdvancedZomato

Corner cycling animation

A 25-minute UIKit exercise. A small logo view has to move through the four corners in order, top-left, top-right, bottom-right, bottom-left, forever, like the…

#uiview-animate #animation #completion #uiviewpropertyanimator

UIKitShort answerAdvancedKREAM

UICollectionView internals

Why use UICollectionView instead of UITableView? Explain it in terms of the internal structure: the layout object, attributes, and reuse.

#uicollectionview #uicollectionviewlayout #layout-attributes #custom-layout

UIKitShort answerAdvancedBaidu

Per-cell countdown with reuse

Each cell in a UITableView flash sale list shows a countdown like "Time left 00:12:34" that ticks down every second. Instead of one Timer per cell, how would…

#uitableview #timer #cell-reuse #prepareforreuse

UIKitShort answerAdvancedMicrosoft

Linked collection and table scrolling

A contacts screen in code review. A horizontally scrolling UICollectionView of letter indexes sits on top, a sectioned UITableView of contacts below; scrolling…

#uicollectionview #uitableview #scrollviewdidscroll #synchronized-scroll

UIKitMultiple choiceAdvancedAlibaba Group

Reused cells and CALayer

When you add layer effects like gradients, shadows, and animations to reusable UIKit cells, which statements describe a real problem and its correct fix? Pick…

#cell-reuse #calayer #shadowpath #gradient

UIKitShort answerAdvancedPinterestunverified source

Flood fill on a large grid

You're implementing flood fill on a large pixel grid drawn with a collection view (say, 500×500). If you don't use recursive DFS, how would you write the…

#collection-view #flood-fill #bfs #batch-updates

Offscreen rendering and the render pipeline

In a UIKit list, you applied layer.cornerRadius plus masksToBounds plus shadow to cells with profile images and the scroll frame rate dropped. From the render…

#rendering #offscreen #core-animation #gpu

Core Animation model and presentation layers

A view animates across the screen over 3 seconds with a UIView animation. Tapping it mid-flight does nothing, and printing view.frame mid-animation already…

#core-animation #presentation-layer #model-layer #animation

Auto Layout performance

On a screen made of complex cells with hundreds of constraints, the layout pass shows up as the bottleneck. Based on how the Auto Layout engine works, what…

#autolayout #performance #cassowary #constraint

UIKit render loop pass order

In one cycle of the main run loop, what's the correct order of the passes UIKit runs to update the screen? (Assume there are views marked with…

#runloop #layout-pass #update-constraints #display

UIKitShort answerExpertNaver Webtoon

Making the case for UICollectionView

The project has hundreds of UITableView screens. You want to propose moving them to UICollectionView. How would you persuade the teammates who object?

#uitableview #uicollectionview #migration #list-configuration