Top 10 iOS Developer Interview Questions with Sample Code & Explanations

View Controller Life Cycle Explained

• 💡 The View Controller Life Cycle involves multiple methods, starting with initializers like init(coder:) and ending with deinit.
• 📌 Key events include loadView, viewDidLoad, viewWillAppear, viewDidAppear, viewWillDisappear, and viewDidDisappear, which can be called multiple times.
• 🔑 Understanding the order and purpose of these callbacks, grouped into initializer, loading, appearance, and layout phases, is crucial.
• ⚠️ A missing deinit call indicates a potential memory leak.

Structs vs. Classes: Value vs. Reference Types

• 🧠 Classes are reference types, meaning multiple instances can point to the same memory location, and changes are reflected across all references.
• 🧩 Structs are value types, typically copied when passed, providing independent instances.
• ⚠️ While structs are generally value-based, Swift employs optimizations like copy-on-write for collections (arrays, dictionaries) and strings, making them appear to be passed by reference under certain conditions.
• 🏦 An analogy: A class is like a bank account (shared reference), while a struct is like a bank statement (independent copy).

Frame vs. Bounds in UIView

• 🎯 The frame property defines a view's size and origin relative to its superview.
• 🖼️ The bounds property defines the view's internal coordinate system, including the origin and size of its content within its own space.
• 🔄 When a view is transformed (e.g., rotated), the frame property's value becomes undefined and should be ignored, while bounds remain consistent.
• ✂️ clipsToBounds property determines if the view's content is clipped to its bounds.

Protocol-Oriented Programming (POP)

• 🚀 POP is a paradigm in Swift that emphasizes protocols over traditional inheritance, offering flexibility and modularity.
• 🔗 Protocols define a blueprint of methods, properties, and other requirements that conforming types must implement.
• 🤝 Unlike Objective-C's class-based inheritance, POP allows structs, enums, and classes to conform to protocols, enabling retroactive modeling and stronger type safety.
• 🗺️ Protocols decouple relationships from concrete types, allowing algorithms to work with any type that conforms to the required protocols, similar to using a map and a list for a specific city without hardcoding the city name.

Swift Concurrency and Coding Challenges

• ⏳ The defer statement executes code just before a scope exits, in reverse order of declaration.
• 🚦 Grand Central Dispatch (GCD) and DispatchQueue are used for managing concurrent operations.
• ⚠️ DispatchQueue.sync on the main queue can lead to deadlocks if it attempts to execute a task that itself depends on the main queue finishing, preventing further tasks (like g) from executing.
• 🔄 Understanding the difference between synchronous and asynchronous operations, as well as serial and concurrent queues, is critical for avoiding issues like deadlocks.

MVC Architecture and Its Components

• 🏗️ Model-View-Controller (MVC) is an architectural pattern separating an application into three interconnected components.
• 📊 The Model manages data and business logic.
• 🖼️ The View handles the user interface and input.
• 🔗 The Controller acts as an intermediary, updating the View based on Model changes and processing user input.
• 🧩 In iOS, UIViewController often tightly couples View and Controller responsibilities, and complex UIs can be managed using child view controllers.

Memory Management: weak and unowned Keywords

• 🔒 weak and unowned keywords are used to prevent strong reference cycles, crucial for memory management.
• 🔗 A weak reference is optional and can be nil, automatically set to nil when the referenced object is deallocated.
• ⚠️ An unowned reference is non-optional and assumes the referenced object will always exist; it will trap if the object is deallocated before the reference.
• 🔌 Delegates in frameworks like UITableView are often declared weak to avoid retain cycles, though exceptions like URLSession delegates exist where they are held strongly.

Lazy Initialization in Swift

• ⚡ lazy keyword defers the initialization of a property until the first time it is accessed.
• 🚀 This is useful for properties that are expensive to initialize or may not be needed, improving performance and reducing memory usage.
• 🔢 lazy can also be applied to collections to create lazy sequences, processing elements only when requested, which is efficient for large datasets.

Escaping vs. Non-Escaping Closures

• 💬 Closures are blocks of code that can be passed around and used in your program.
• ➡️ An escaping closure can be stored and called at a later time, outside the scope of the function it was passed to (e.g., completion handlers).
• ❌ A non-escaping closure must be executed within the scope of the function it was passed to and cannot be stored for later use.
• ⚙️ As of Swift 5.0, non-escaping closures are the default, requiring the @escaping attribute to explicitly mark closures that can escape.