Did you know that the average iOS developer salary in the US is over $140,000? With over 1 billion active iOS devices worldwide, iOS development skills are in high demand. But with great demand comes great competition, and nailing the iOS interview is key to landing your dream job. We put together this guide on the top 25 iOS interview questions. With the right preparation, you’ll be ready to ace any iOS interview that comes your way!
This guide has got you covered from iOS interview questions for beginners to more advanced swift interview questions for experienced developers. Let’s get started!
iOS Interview Questions for Freshers
Just getting started with iOS development? Here are some common iOS interview questions and answers to get up to speed:
- What is Swift and why is Swift preferred over Objective-C?
Swift is a robust and intuitive programming language created by Apple for iOS development. It improves upon Objective-C with features like type safety, concise syntax, and faster performance.
- What are frameworks in iOS? Name some commonly used frameworks.
Frameworks are reusable libraries or blocks of code that provide common functionality iOS developers can leverage. Some common iOS frameworks are UIKit, Core Data, SpriteKit and ARKit.
- What is Cocoa Touch in iOS development?
Cocoa Touch refers to the key frameworks used to build iOS applications with native look-and-feel and performance, like UIKit, MapKit, GameKit etc.
- What are delegates in iOS and what is their purpose?
Delegates allow customization of UIKit components like passing data or handling events. They follow the delegation design pattern where object states are synchronized by one object (the delegate) on behalf of another object.
- What is Auto Layout in iOS? What are its benefits?
Auto Layout allows defining rules/constraints for UI element positioning so they display properly across different device screens. Key benefits are increased flexibility and reduced maintenance effort.
iOS Interview Questions for Experienced Developers
Ready to show off your chops? Here are some advanced swift interview questions:
- What are the differences between classes and structs in Swift?
Classes are reference types, allowing inheritance and deinitializers while structs are value types allowing mutating methods and late initialization. Value types are also better performant.
- Explain Swift optionals and how to handle them.
Optionals represent a variable that may be nil. Unwrapping with “if let” checks for a value before using. Force unwrapping with “!” just assumes existence of value.
- What is a memory leak in reference types like classes and how can you avoid it?
It happens when reference types are not deallocated properly. Using weak references avoids strong reference cycles between instance properties, preventing memory leaks.
- How are closures implemented under the hood in Swift?
Closures are implemented as reference types that capture constants and variables from context. Each closure results in allocation of a special class instance to store these referenced values when called.
- What are the differences between composition and inheritance?
While inheritance promotes tight coupling of parent and child classes, composition simply aggregates behaviors from contained instances through protocols giving more flexibility.
iOS Interview Questions on App Lifecycle
Whether for iOS developer or swift developer interviews, app lifecycle handling is crucial.
- Explain the iOS app lifecycle.
The iOS app lifecycle has states like inactive, active, background and suspended, managed automatically via callbacks like applicationDidEnterBackground or sceneDidDisconnect.
- How do you handle app state transitions and background execution?
Implement the UIApplicationDelegate callbacks to handle state transitions. Enable background modes or async tasks with processors like BGAppRefreshTask for background execution.
iOS SwiftUI Interview questions
With SwiftUI gaining traction as the next-gen UI framework, expect SwiftUI interview questions like:
- What is SwiftUI and what are its major benefits?
SwiftUI is a declarative UI framework to compose rich iOS interfaces using simple, readable code. Key benefits are improved code readability, less bugs and seamless integration with new Apple platforms.
- Explain how SwiftUI uses some key concepts like Views, Modifiers and Bindings.
In SwiftUI, Views describe UI components, Modifiers customize them, and Bindings connect interface to data model synchronously. This separation of concerns results in simpler, safer code.
- What are the differences between @State, @Binding and @EnvironmentObject?
@State holds private UI state, @Binding passes limited UI state while @EnvironmentObject shares observable data model across View tree.
iOS Interview Questions on Design Patterns
Given the complexity of iOS apps, being familiar with key design patterns is a must:
- Explain the Observer design pattern and its implementation options in iOS.
Allows broadcasting updates to registered observers. Implemented via delegation, NotificationCenter or reactive libraries like Combine.
- Explain Singleton design pattern and an example usage in iOS
Ensures only one instance exists. Managers like FileManager, DataManager or Configs are often implemented as Singleton.
- What design pattern does MVC represent and how is it implemented in iOS?
MVC or Model View Controller separates data, presentation and logic concerns for easier maintenance. Implemented via UIViewController, Views and Model classes in iOS.
iOS Interview Questions on Core iOS Frameworks
Whether for swift developer interview questions or iOS interview questions and answers for experienced, knowledge of Core iOS frameworks is a must.
- What are some commonly used iOS frameworks and their key capabilities?
UIKit: User interface, gestures handling
CoreData: Object graph and persistence
CloudKit: Backend as a Service on iCloud
AVFoundation: Audiovisual media playback and synthesis
Spritekit: 2D game engine and physics simulation
ARKit: Augmented reality capabilities
- What are some key features of Core Data in iOS for handling persistence?
Core Data handles object lifecycle and threading, change tracking, background data saving and efficient fetching using SQLite store.
iOS Interview Questions on Architecture Patterns
Solid architecture ensures scalable and maintainable iOS apps. Common iOS architecture interview questions include:
- What are the advantages of using design patterns like MVVM over MVC?
MVVM keeps controllers simpler, moves business logic to ViewModels improving testability and introduces data binding for faster development.
- Explain common architecture patterns like VIPER used for enterprise iOS apps
VIPER has View, Interactor, Presenter, Entity and Routing layers – promoting modularity and testability with clear separation of concerns.
- How can iOS apps implement clean architecture with dependency injection?
Wrapping services in protocols allows injecting mock implementations. Libraries like Swinject can instantiate dependencies defined in Service Locator keeping business logic isolated.
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iOS Interview Questions on Testing
With iOS complexity, solid testing skills are a must. Common iOS testing interview questions include:
- What types of testing are performed on iOS apps?
iOS apps are tested via unit testing isolated components, UI testing using simulators, performance testing, integration testing with mocks and behavior testing through test doubles.
- What are some popular iOS testing frameworks and their key capabilities?
XCTest allows tests in OC or Swift. Quick/Nimble facilitates behavior testing. OCMock and OHHTTPStubs help stub network. SwiftUI Previews builds quick UI iterate validation.
iOS Interview Preparation Tips
Here are some top tips to help prepare for your next iOS interview:
- Practice iOS programming interview questions on Swift and common frameworks
- Understand iOS architecture patterns like MVC, MVVM and VIPER
- Brush up on Swift language features like optionals and closures
- Prepare an iOS app code sample illustrating good architecture
- Read up on Apple Human Interface Guidelines for iOS and common UI patterns
- Revise application lifecycle concepts in iOS
By mastering these key topics, you’ll be ready to tackle any iOS interview questions that come your way!
Conclusion
We hope you enjoyed this overview of the top 25 iOS interview questions and answers. Want to land a top iOS developer job? Explore open listings on leading tech job sites leveraging the power of Hirist mobile app for a smooth application experience right from your smartphone! All the best!
