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With over 1.46 billion active Apple devices worldwide, iOS development remains one of the most lucrative and competitive fields in tech. Whether you’re a junior iOS developer or a senior engineer, preparing for iOS developer interview questions is crucial to landing your dream job at top companies like Apple, Google, or Uber.

This comprehensive guide covers:

• Swift & SwiftUI fundamentals
• Memory management
• UIKit vs SwiftUI
• Design patterns
• System design questions
• Behavioral questions

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30 Essential iOS Developer Interview Questions

Swift Fundamentals

1. What are the key differences between Swift and Objective-C?

Answer:

Feature	Swift	Objective-C
Syntax	Clean, modern	Verbose, C-style
Memory Management	Automatic (ARC)	Manual or ARC
Performance	Faster runtime	Slower message dispatch
Null Safety	Optionals	No null safety

2. Explain Optionals in Swift

Answer:
Optionals handle the absence of a value:

swift

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var name: String? = nil
name = "John"
if let unwrappedName = name {
    print(unwrappedName) // Safely unwrapped
}

3. What is the difference between weak and unowned references?

Answer:

• weak: Optional, becomes nil when object deallocates
• unowned: Non-optional, assumes object exists (risk of crashes)

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UIKit & SwiftUI

4. Compare UIKit and SwiftUI

Answer:

Aspect	UIKit	SwiftUI
Paradigm	Imperative	Declarative
Live Preview	No	Yes
Adoption	All iOS versions	iOS 13+
State Management	Manual	@State, @Binding

5. How does @State work in SwiftUI?

Answer:
@State is a property wrapper for mutable view data:

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struct CounterView: View {
    @State private var count = 0 // Triggers view update when changed
    
    var body: some View {
        Button("Tap me \(count)") { count += 1 }
    }
}

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Memory Management

6. What is a retain cycle and how do you prevent it?

Answer:
A retain cycle occurs when two objects hold strong references to each other. Solutions:

• Use weak or unowned for delegates/closures
• Break cycles in deinit

7. Explain ARC in iOS

Answer:
Automatic Reference Counting (ARC) manages memory by:

• Increasing retain count when references are added
• Deallocating objects when retain count = 0

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Concurrency

8. Compare DispatchQueue, OperationQueue, and async/await

Answer:

Method	Pros	Cons
DispatchQueue	Lightweight	No dependency management
OperationQueue	Dependencies, cancelable	Overhead
async/await (Swift 5.5+)	Clean syntax	iOS 15+

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System Design

9. How would you implement a caching system for images?

Answer:

swift

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class ImageCache {
    static let shared = NSCache<NSString, UIImage>()
    
    static func get(url: String) -> UIImage? {
        return shared.object(forKey: url as NSString)
    }
    
    static func set(url: String, image: UIImage) {
        shared.setObject(image, forKey: url as NSString)
    }
}

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Behavioral Questions

10. Describe a challenging iOS bug you fixed

Sample Answer:
“I once debugged a memory leak in a video player by:

1. Using Instruments’ Allocations tool
2. Finding a retain cycle between the player and its delegate
3. Fixing it with weak self in closures”

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People Also Ask

Q1: What is MVVM in iOS?

A: Model-View-ViewModel separates:

• Model: Data logic
• View: UI (SwiftUI/UIKit)
• ViewModel: Business logic

Q2: Is UIKit still used in 2024?

A: Yes! Many apps still use UIKit, especially those supporting iOS 12 or earlier.

Q3: What’s the salary range for iOS developers?

A: In the US:

• Junior: 80K–80K–120K
• Senior: 130K–130K–220K
• FAANG: 200K–200K–350K+

Q4: How do I prepare for an iOS architecture interview?

A: Study:

• VIPER vs MVC vs MVVM
• Dependency injection
• Protocol-oriented programming

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Conclusion

Mastering these iOS developer interview questions requires:

1. Deep Swift knowledge (optionals, ARC, concurrency)
2. Framework expertise (UIKit/SwiftUI)
3. System design practice (caching, networking)
4. Clean code principles

Need more help? Check out:

• Apple’s Swift Documentation
• Ray Wenderlich Tutorials