100+ IOS Developer Interview Questions and Answers

Use Instruments tool to identify memory leaks in iOS projects

• Use Instruments tool provided by Xcode to run the app and analyze memory usage

• Look for memory leaks in the Allocations and Leaks instruments

• Check for any objects that are not being deallocated properly, causing memory leaks

Steps to add collection view in Swift.

• Create a UICollectionView instance

• Set the delegate and data source of the collection view

• Implement the required methods of UICollectionViewDataSource and UICollectionViewDelegate protocols

• Register the cell class or nib file for the collection view

• Return the number of items and configure the cell in the data source methods

• Implement any additional delegate methods as needed

MVVM is a design pattern that separates UI code from business logic and data models.

• MVVM stands for Model-View-ViewModel

• Model represents the data and business logic

• View displays the UI and user interactions

• ViewModel acts as a mediator between Model and View

• ViewModel exposes data and commands to View

• MVVM helps in testability, maintainability and scalability of code

There are designated initializers in Swift that have specific behaviors, such as convenience init and required init.

• Designated initializers are primary initializers for a class and must call a designated initializer from its superclass.

• Convenience initializers are secondary initializers that must call another initializer in the same class.

• Required initializers must be implemented by all subclasses of a class.

Optional binding in Swift helps to safely unwrap optionals and check for nil values.

• Use if let or guard let to safely unwrap optionals and bind the value to a new constant or variable.

• Check for nil values before using the unwrapped value to avoid runtime errors.

• Example: if let name = optionalName { print(name) }

• Example: guard let age = optionalAge else { return }

URLSession is a class in iOS that allows you to make network requests and handle responses.

• URLSession is used to create tasks for fetching data from the internet.

• It supports various types of tasks such as data tasks, download tasks, and upload tasks.

• You can configure URLSession with URLSessionConfiguration to customize its behavior.

• Example: URLSession.shared.dataTask(with: url) { (data, response, error) in }

Dispatch Queue is a high-level API for managing concurrent operations, while OperationQueue is built on top of Dispatch Queue and adds additional features for managing operation objects.

• Dispatch Queue is a lightweight way to execute tasks serially or concurrently, while OperationQueue is used to manage operation objects that represent tasks.

• OperationQueue allows for dependencies between operations, while Dispatch Queue does not have built-in support for dependencies.

• Dispatch ...read more

MVC is a design pattern that separates an application into three main components: Model, View, and Controller. MVVM is a variation of MVC with an added ViewModel layer.

• MVC stands for Model-View-Controller, where Model represents the data, View represents the UI, and Controller acts as an intermediary between Model and View.

• MVVM stands for Model-View-ViewModel, which adds a ViewModel layer between the View and Model. ViewModel exposes data and methods to the View.

• In MVC, the V...read more

The code prints 'Hello World' to the console.

• The code uses the print function to output 'Hello World'.

• There are no variables or conditions involved in the output.

Swift is a programming language developed by Apple for iOS, macOS, watchOS, and tvOS development.

• Swift is a modern, fast, and safe programming language.

• It is designed to work seamlessly with Apple's Cocoa and Cocoa Touch frameworks.

• Swift is used to develop applications for iOS, macOS, watchOS, and tvOS.

• It is open-source and has a large community of developers contributing to its growth.

• Swift is known for its concise syntax and powerful features like optionals, closures, and g...read more

Protocols in iOS define a blueprint of methods, properties, and other requirements that can be adopted by classes, structs, or enums.

• Protocols are used to define a set of methods and properties that a class, struct, or enum must implement.

• They allow for polymorphism and code reuse by enabling multiple classes to conform to the same protocol.

• Protocols are commonly used in delegation, where one object delegates tasks to another object that conforms to a specific protocol.

• They a...read more

A protocol is a set of rules or guidelines that define how objects interact with each other in a specific context.

• Protocols define methods that a class must implement to conform to the protocol

• They can also define properties, initializers, and associated types

• Classes, structs, and enums can adopt protocols to inherit their behavior

Higher order functions in Swift are functions that can take other functions as parameters or return functions as results.

• Examples of higher order functions in Swift include map, filter, and reduce.

• Higher order functions help in writing cleaner and more concise code by abstracting away common patterns.

• They promote functional programming principles by treating functions as first-class citizens.

The flow of API implementation can be designed using design patterns and unit testing.

• Identify the design patterns suitable for the API implementation

• Create a flow diagram to visualize the steps involved

• Implement the API using the chosen design patterns

• Write unit tests to ensure the functionality and reliability of the API

• Refactor and optimize the code as needed

Reduce application size by optimizing images, removing unused code, using ProGuard, and splitting APKs.

• Optimize images by using tools like ImageOptim or TinyPNG.

• Remove unused code and resources to reduce unnecessary bloat.

• Use ProGuard to shrink, optimize, and obfuscate code.

• Split APKs to only include necessary resources for each device configuration.

Handle reference cycles by using weak or unowned references to break the strong reference cycle.

• Use weak or unowned references to break strong reference cycles

• Weak references do not keep a strong hold on the instance they refer to

• Unowned references assume that the instance they refer to will never be nil

Weak & Unowned references are used in ARC to prevent retain cycles in Swift programming.

• Weak references do not increase the retain count of an object, and automatically become nil when the object is deallocated.

• Unowned references do not keep a strong reference to the object, and can become a dangling pointer if the object is deallocated.

• ARC (Automatic Reference Counting) is a memory management system used in Swift to automatically manage memory for objects.

ARC stands for Automatic Reference Counting, a memory management system used in iOS development. Retain count is the number of references to an object.

• ARC is a memory management system in iOS that automatically tracks and manages memory usage.

• Retain count is the number of strong references to an object, which determines when the object should be deallocated.

• When an object's retain count reaches 0, it is deallocated from memory to free up resources.

• ARC helps prevent memory lea...read more

Class and struct are both used to define custom data types in Swift.

• Class is a reference type, while struct is a value type.

• Classes support inheritance, while structs do not.

• Classes have deinitializers, while structs do not.

• Structs have memberwise initializers, while classes do not.

• Examples of classes: UIViewController, NSObject.

• Examples of structs: CGPoint, CGRect.

Test cases will be written using XCTest framework and will cover all possible scenarios.

• Identify all possible scenarios and edge cases

• Write test cases using XCTest framework

• Ensure test cases cover all scenarios and edge cases

• Test cases should be automated and run on a regular basis

The design pattern used for an app and its architecture is crucial for scalability and maintainability.

• Use MVC (Model-View-Controller) for separating data, presentation, and user interaction.

• Consider MVVM (Model-View-ViewModel) for better separation of concerns and testability.

• Implement Dependency Injection to make components loosely coupled and easier to test.

• Use Singleton pattern for managing shared resources like network calls or database connections.

• Consider using Clean A...read more

Solid principles are a set of five design principles for writing maintainable and scalable code.

• Single Responsibility Principle: A class should have only one reason to change.

• Open/Closed Principle: Classes should be open for extension but closed for modification.

• Liskov Substitution Principle: Objects of a superclass should be replaceable with objects of its subclasses without affecting the program's correctness.

• Interface Segregation Principle: Clients should not be forced to ...read more

Structs are value types, classes are reference types. Singletons ensure only one instance of a class. MVC separates concerns, MVVM adds a ViewModel layer.

• Structs are lightweight and copied by value, while classes are more powerful and passed by reference.

• Singletons are useful for global state and ensuring only one instance of a class exists.

• MVC separates concerns by dividing code into Model, View, and Controller components.

• MVVM adds a ViewModel layer between the View and Mode...read more

Computed properties are properties in Swift that do not store a value directly, but instead provide a getter and an optional setter to retrieve and set their value.

• Computed properties do not have a backing store like stored properties.

• They are used to calculate a value on-the-fly based on other properties or data.

• Example: calculating the area of a square based on its side length.

The mutating keyword is used in Swift to indicate that a method is allowed to modify the properties of a value type.

• Used in Swift with value types like structs and enums to allow methods to modify their properties

• Prevents compilation error when attempting to modify properties of a value type within a method

• Example: mutating func updateValue(newValue: Int) { self.value = newValue }

Conditionals are statements in programming that allow for different actions to be taken based on whether a certain condition is true or false.

• Conditionals are used to make decisions in code based on specified conditions.

• They typically involve if-else statements or switch-case statements.

• Examples include if (condition) { // do something } else { // do something else }

• Another example is switch (variable) { case value1: // do something; break; case value2: // do something else; ...read more

if let unwraps an optional value if it exists, guard statement unwraps an optional value and exits the scope if it doesn't exist

• if let is used to safely unwrap an optional value and assign it to a new variable within the scope

• guard statement is used to unwrap an optional value and ensure it exists for the rest of the scope, otherwise it exits the scope

• if let example: if let name = optionalName { print(name) }

• guard example: guard let age = optionalAge else { return }

Environmental objects refer to physical entities in the environment that can be interacted with or manipulated by the user or application.

• Environmental objects can include items like trees, buildings, vehicles, and furniture in a virtual reality environment.

• These objects can be programmed to have specific behaviors or properties, such as collision detection or physics simulations.

• Interacting with environmental objects can enhance user immersion and engagement in the virtual e...read more

MVC architecture is a design pattern used in software development to separate the application into three main components: Model, View, and Controller.

• Model represents the data and business logic of the application.

• View is responsible for displaying the data to the user.

• Controller acts as an intermediary between Model and View, handling user input and updating the Model accordingly.

• MVC helps in organizing code, improving maintainability, and promoting reusability.

• Examples of M...read more

Retain cycle occurs when two objects hold a strong reference to each other, preventing them from being deallocated.

• Occurs in iOS development when two objects have strong references to each other

• Can lead to memory leaks as the objects are never deallocated

• Prevented by using weak or unowned references in Swift

I have used MVC, MVVM, and VIPER architectures in iOS development.

• MVC (Model-View-Controller): Separates data, presentation, and user interaction.

• MVVM (Model-View-ViewModel): Enhances separation of concerns and testability.

• VIPER (View-Interactor-Presenter-Entity-Routing): Provides clear separation of components.

Local data is managed using Core Data framework in iOS development.

• Use Core Data framework to create, read, update, and delete local data.

• Utilize entities, attributes, and relationships to model the data.

• Implement fetch requests to retrieve data based on specific criteria.

• Use NSManagedObject subclasses to represent data objects.

• Utilize NSPersistentContainer to manage the Core Data stack.

GCD (Grand Central Dispatch) is a concurrency framework that allows developers to perform tasks asynchronously.

• GCD is used to manage concurrent operations in iOS apps.

• It uses dispatch queues to manage tasks and execute them in parallel.

• GCD provides different types of queues such as serial, concurrent, and main queues.

• Example: DispatchQueue.main.async { // code to be executed on main queue }

• Example: DispatchQueue.global(qos: .userInitiated).async { // code to be executed on a ...read more

Protocol Oriented Programming is a programming paradigm in Swift that focuses on defining protocols to define behavior.

• POP is a way of designing code by defining protocols that describe a set of behaviors.

• It encourages composition over inheritance, allowing for more flexible and reusable code.

• By using protocols, you can define a blueprint of methods and properties that a type must implement.

Protocols in iOS are a set of rules that define methods and properties that a class must implement.

• Protocols are similar to interfaces in other programming languages.

• They allow for communication between classes that may not have a direct relationship.

• Classes, structs, and enums can adopt protocols.

• Example: UITableViewDelegate protocol is adopted by classes to handle table view data and interactions.

To push an app on the Apple store, you need to create an Apple Developer account, prepare your app for submission, submit it for review, and then release it to the store.

• Create an Apple Developer account

• Prepare your app for submission by following Apple's guidelines

• Submit your app for review through the App Store Connect portal

• Wait for Apple to review your app and provide feedback

• Once approved, release your app to the Apple store for users to download

Generics in Swift allow you to write flexible, reusable functions and types that can work with any type.

• Generics enable you to write functions and types that can work with any type.

• They help in writing flexible and reusable code.

• Example: Array can hold elements of any type T.

Table view displays data in a single column, while collection view allows for more complex layouts with multiple columns and rows.

• Table view is typically used for displaying lists of data in a single column.

• Collection view allows for more flexibility in layout, with support for multiple columns and rows.

• Collection view can also display data in a grid layout, while table view is limited to a single column.

• Table view is more suitable for simple, linear data presentation, while ...read more

I used Combine to handle asynchronous events and data streams in my iOS app development.

• Used Combine to manage network requests and responses

• Implemented Combine to handle user input and UI updates

• Utilized Combine to combine multiple data streams and perform operations on them

MVVM is an architectural design pattern that separates the user interface code from the business logic and data model.

• MVVM stands for Model-View-ViewModel

• Model represents the data and business logic

• View displays the UI elements and interacts with the user

• ViewModel acts as a mediator between the Model and View, handling user inputs and updating the Model

• MVVM helps in achieving separation of concerns and making the code more modular and testable

Serialisation in API is the process of converting data into a format that can be easily transmitted over a network.

• Serialisation is used to convert complex data structures into a format that can be easily transmitted over a network.

• It involves converting objects or data structures into a stream of bytes that can be sent over a network.

• JSON and XML are commonly used formats for serialising data in APIs.

• Serialisation is important for ensuring data consistency and interoperabili...read more

The application lifecycle inside app delegate manages the state transitions of the app.

• The app delegate methods like applicationDidFinishLaunching, applicationWillResignActive, applicationDidEnterBackground, applicationWillEnterForeground, applicationWillTerminate, etc. handle different states of the app.

• These methods are called by the system at specific points during the app's lifecycle.

• Developers can use these methods to perform tasks like initializing app data, saving stat...read more

Delegate pattern is a design pattern in which an object delegates some of its responsibilities to another object.

• Create a protocol defining the methods that the delegate should implement

• Declare a delegate property in the delegating class

• Set the delegate property to the object that will act as the delegate

• Call the delegate methods from the delegating class

Best practices for handling memory leaks in iOS development

• Use Instruments to identify memory leaks

• Avoid strong reference cycles with weak or unowned references

• Use autorelease pools for temporary objects

• Implement proper memory management with ARC (Automatic Reference Counting)

The architecture of an iOS app refers to the overall structure and organization of its code.

• iOS apps typically follow the Model-View-Controller (MVC) architecture pattern.

• The Model represents the data and business logic, the View displays the user interface, and the Controller manages the interactions between the Model and View.

• Other popular architecture patterns for iOS apps include VIPER, MVVM, and Clean Architecture.

• Choosing the right architecture depends on the specific n...read more

I follow the MVC (Model-View-Controller) design pattern in my iOS development.

• Separates data (Model), user interface (View), and control logic (Controller)

• Improves code organization and maintainability

• Promotes reusability and scalability

• Examples: UIKit framework in iOS uses MVC pattern

Swift is a modern, fast, and safe programming language developed by Apple, while Objective-C is an older, more verbose language.

• Swift is more concise and easier to read than Objective-C.

• Swift supports optionals and type inference, making code safer and less prone to errors.

• Objective-C requires manual memory management with retain and release, while Swift uses automatic reference counting (ARC).

• Swift is interoperable with Objective-C, allowing developers to use both languages ...read more