300+ Questions: Mastering the IOS Technical Interview

Discover multiple approaches to laying out UIView elements, from interface builder with storyboards to code-based layouts using exact CGRect coordinates, including options to work without storyboards.

Master auto layout by using constraints to define location and size of views for varying device sizes and orientations, including spacing, height, width, and priority in Interface Builder or code.

Explore how to implement iOS multi-threading with Grand Central Dispatch, create a queue, add a block, dispatch async, perform background tasks like downloading a file, and then update the UI.

Clarify the difference between bounds and frame: bounds define the view's internal coordinates with an origin at zero, while frame defines its position and size in the superview.

Master animating a view with constraints by resetting constraints, laying out the parent before the animation, and animating inside the animation block to ensure everything is aligned.

Explore the main concurrency approaches in iOS and macOS, including Grand Central Dispatch, dispatch queues, and operation queues, with their strengths, weaknesses, and when to choose each.

Define app id and bundle id and explain their differences: app id combines a team id with a unique string; bundle id identifies a single app or set.

Compare assign vs retain: assign is used for scalar types like float and does not own the value, while retain denotes ownership and can be dynamic based on the situation.

Explain how code coverage measures the value of unit tests as a percentage, such as 70% or 80%, and how teams use it to gauge progress in meetings.

Explore how Cocoa and Cocoa Touch enable mac and iOS app development via the Objective-C runtime, with Cocoa containing Foundation and AppKit and Cocoa Touch containing Foundation and UIKit.

Describe a managed object context as a temporary scratchpad for fetched objects, providing an internally consistent view; modify objects within the context, but the persistence store stays unchanged until saved.

Design a robust image loading approach for iOS apps: download images from a remote server as the user scrolls, on a background thread, with cell validation and optional image caching.

Explore dynamic dispatch as the runtime selection of a polymorphic method and understand how the compiler and final keyword influence static versus dynamic calls on base classes.

Learn how to add iOS frameworks, switch from product to target, drag and drop frameworks, and then check the directory to ensure they are added in the proper location.

Layer objects are data objects that represent visual content and render that content in the interface. Add layer options to enable complex animations and visual effects, including corner radius adjustments.

Core animation relies on layer objects as the heart of rendering, with CALayer driving most visual content. Learn how developers enable and manage layers to decide what to render.

Store private user data securely on device offline using keychain with pin codes or encrypted databases, and consider remote servers over ssl with certificate pinning and data validation.

Identify and reproduce app crashes by isolating environmental factors and device details, analyze crash logs and memory leaks, and apply unit tests and debugging to optimize UI and background tasks.

Examine the model-view-controller design pattern for separating UI logic, detailing view, controller, and data model roles, common pitfalls, and alternatives like MVP or VIPER.

Discover how the autorelease pool manages memory by controlling the release cycle and freeing objects at the right time to optimize iOS app performance.

Discover how iBeacons use Bluetooth Low Energy to let mobile apps listen for beacon signals in the physical world, determine precise location, and deliver contextual content to users.

Explore SpriteKit and SceneKit as iOS frameworks that simplify game development, enable 3D graphics, object and physics property manipulation, and on-screen rendering to produce games.

Compare Swift and Objective-C, highlighting Objective-C's dynamic runtime and C heritage, Swift's safer, type-safe syntax, bridging between them, and the value of knowing both for legacy code.

Explain when an app is not running, how the system suspends or terminates it, and how to view or terminate running apps.

Describe how an iOS app transitions from locked or not running into inactive, then into active and background states upon launch, before briefly reaching the suspended state.

Write test scripts to exercise applications with UI automation API, simulate user interactions, and return log information to the host computer by creating a new project and selecting two checkboxes.

Master threading to keep the user interface responsive by running heavy tasks on background threads and performing user interface work on the main thread, with progress indicators during loading.

Identify UIKit as the framework for iOS user interfaces, including event handling, views, and touchscreen controls. Interface Builder controls use the UI prefix to signal they belong to UIKit.

Explore the five iOS application states—not running, inactive, active, background, and suspended—and learn how transitions and memory conditions affect app behavior.

Present modally displays a view on top of the navigation stack, without pushing it, and hides the navigation bar, returning to the prior screen when dismissed.

Explore how strong and weak references govern memory management, how mutual strong references cause memory leaks, and why Interface Builder uses weak references to prevent cycles.

Explore strong versus weak references in a parent–child model, with a strong reference from parent to child and a weak reference from child to parent, using employee and employer examples.

Understand how reuse identifiers group similar table rows and recycle cells to allocate memory only for visible content during scrolling.

Learn how to replace c-style loops with a stride function to iterate from zero to ten by one, printing each value.

Explain how the ~/Library, ~/Documents, and ~/tmp directories manage files, temporary data, and user content, including visibility, backups to iTunes and iCloud, and file sharing.

Master sandboxing to protect user systems by limiting app privileges, using Mac OS access control and developer ID signed apps distributed outside the store to contain damage and deter malware.

Explore how a wildcard app id uses an asterisk to represent variable parts, enabling a bundle of apps with the same prefix to fall under one app id.

Explore representational state transfer and how its stateless client-server model, cacheable data, uniform interface, and layered system enable scalable, modular architecture with code on demand.

Identify common reasons for App Store rejection, including bugs, crashes, broken links, placeholder content, incomplete or misleading descriptions, noncompliant UI, and excessive ads, to improve submission quality.

Master the process to push an app to the App Store, including creating the bundle identifier, certificate signing request, production certificate, provisioning profile, listing details, SEO tactics, versioning, and submission.

Explain the differences between developer and enterprise accounts, focusing on distribution, access, and cost. Note the $99 developer fee and enterprise pricing of 2.9 per year, for internal crm apps.

Explain how the notification center manages local and push alerts, including background delivery, and how APNs delivers data to iOS, tvOS, watchOS, and macOS devices.

Explain two memory leak cases, including retaining cycles with strong references that never release. See how ARC and low-level classes lacking RC cause leaks, crashes, and high memory use.

Explore how NSUserDefaults stores simple data types to persist user-specific information between app launches, using keys, defaults, and the standard user defaults to read and write values.

Explore the difference between viewDidLoad and viewDidAppear, initializing data once and performing layout when visible, while minimizing server calls on subsequent appearances.

Compare viewDidLoad and viewDidAppear for loading remote server data. Choose caching for static data and refreshing for frequently changing data to balance real-time needs.

Wait for a thread to finish before starting another using a selector on the main thread, keeping the user interface responsive with a busy indicator until data updates.

Explore how layers represent rectangles with visual content, manage image-based content, and animate within Core Animation. Learn how layers provide visual attributes and track position, size, and transformed property.

Explore UI controls by examining concrete subclasses like buttons, segment controls, and switches, and learn how properties, functions, and selectors trigger events and handle data properties.

Master the decisions around overriding drawRect, use setNeedsDisplay to trigger drawing, supply the correct drawing context, and avoid blank black boxes by leveraging layer properties for custom rendering.

Explore the singleton pattern and how cramner's singleton class returns the same instance across requests, with iOS examples like file manager, UIAccelerometer, and session.

Explore whether UIKit is thread-safe by examining drawing to graphics contexts and manipulating graphics concepts across multiple threads, and why unsafe code can cause unintended consequences and affect performance.

Use the leaks instruments to measure memory usage, identify objects no longer referenced, reproduce scenarios, and follow steps to fix memory leaks.

Discover how to execute code while an iOS app runs in the background by registering a background task with a 10–15 minute limit, enabling downloads to continue after suspension.

Explore iOS view lifecycle events, from view did load for setup to view will appear and view did disappear for updates and transitions, plus cleanup via did unload and dispose.

Store user info securely with the keychain for usernames and passwords, accessible only to your app, as Apple’s encrypted storage guides suggest for small data chunks and file-system databases.

Contrast Swift and Objective-C with focus on type inference, optionals, and playgrounds for safer code. Swift is the future; balance proficiency in both languages to leverage C and Objective-C libraries.

Explore common iOS UI elements such as buttons, text fields, images, and labels, and learn how to implement them with Interface Builder, code from scratch, or layout constraints.

Explore XCTest features in Xcode, including test cases, abstract base classes, test targets and bundles, arranging the flow of execution through separate test methods, async operations, and performance tests.

Compare unit tests with UI testing and learn to isolate a unit’s features, functions, and methods to run a focused test suite that validates pure code functionality.

Explore SQLite, a lightweight, self-contained engine with fast performance, iOS and Mac OS support, and strong community backing, though not as robust as sequel server.

Categories extend functionality by adding methods to an existing class, such as in the Cocoa framework, distribute implementations across separate files, and group large methods into categories for modular code.

Explore the advantages and disadvantages of categories in Objective-C, including extending any class without source and structuring code across units, noting you cannot override methods defined in the class.

Master four major data types: string, floats, integers, and booleans; learn their characteristics, such as strings of characters, floats as decimal numbers, and booleans as true or false.

Explore how the synthesized keyword in Objective-C generates getter and setter methods for a property, communicates with the compiler, and creates an instance variable—though it is optional today.

Explain how the dynamic keyword enables runtime message interception in Objective-C and how a superclass property outlet is wired in a subclass.

Define and adopt protocols in objc, using required and optional methods to send messages and create reusable data source patterns for table views.

Explore the differences between include and import: include may duplicate a file, while import reads it once, with header protections preventing multiple inclusions.

Explain formal protocols in ObjC and how they declare required or optional methods, adoption in type checking, and inheritance from ancestors. Include informal protocols and how they influence protocol design.

Explore the difference between synchronous and asynchronous blocks using perform block, showing how execution order changes and when the program waits for a block to finish on a separate thread.

Learn why atomic properties guarantee fully initialized values by default, and see how non-atomic options trade safety for performance when a precise value isn't required.

Explore iOS background modes that enable audio playback, background location updates, VoIP, external accessory communication, Bluetooth and Core Bluetooth, Newsstand interactions, remote notifications, and background downloads to keep apps responsive.

Learn to work with crash logs by locating and importing x-archive files, matching exact version strings from the application properties, and organizing crash data in the crash logs devices window.

Discover persistence stores, including in-memory, light stores, and binary stores, and learn when to use each type for readability, performance, and atomic data handling in large datasets.

Explain how the persistent store coordinator links stores to the core data model and mediates between stores and the managed object context in the core data stack.

Determine when code is thread safe by ensuring correct behavior under simultaneous execution of multiple threads regardless of scheduling interleaving, with no additional synchronization or coordination in the calling code.

Learn when to use weak references for self in a block, and how to adopt a strong self inside the block to avoid retain cycles and premature deallocation.

Examine ARC, a memory management feature that uses retain and release to manage reference counts and deallocate objects when zero, contrasting with garbage collection and promoting weak references.

Compare ARC and MRC to reveal memory management differences, noting ARC's automatic reference counting and lack of runtime penalty versus MRC's manual release and reference tracking.

Explain the difference between copy and retain: retain increments the object's retain count and preserves ownership, while copy creates a new data copy and assigns it to a new variable.

Explore the difference between strong and retain in memory management, showing they are virtually the same in use and why retain remains a legacy convenience from older days.

Analyze strong vs weak references in iOS memory management, showing how strong references create owner relationships that prevent deallocation, while weak references avoid ownership.

Compare weak and unowned references: weak is optional and may nil, while unowned is not optional and can crash if deallocated, so use unowned only when a value exists.

Master iOS memory management by guiding object lifecycles and freeing memory when no longer needed, and focus on breaking reference cycles to deallocate and use less memory.

Identify retain cycles that cause memory leaks by understanding mutual references and use instruments and tools to detect and prevent memory release failures.