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30+ iOS Interview Questions And Answers

iOS is an operating system created by Apple Inc. for its mobile devices, including the iPhone, iPad, and iPod Touch. It's widely used for developing mobile apps, which makes expertise in iOS development a sought-after skill. iOS interview questions often cover a range of topics from basic programming concepts to advanced technical skills required for veteran developers.


Most asked iOS interview questions



What is the purpose of the AppDelegate file?

AppDelegate is a central point of control and coordination for apps in iOS. It works with the app to handle startup, state transitions, and other system-wide events.


Can you explain what a closure is in Swift?

A closure in Swift is a self-contained block of functionality that can be passed around and used in your code. It's similar to a function, but it can capture and store references to variables and constants from the surrounding context.


What is the difference between a struct and a class in Swift?

The main differences are that structs are value types and classes are reference types. Structs are copied when they are assigned to a new variable or constant, or when they are passed to a function. Classes, however, are passed by reference.


What does the 'weak' keyword do?

The 'weak' keyword indicates a reference that does not keep a strong hold on the object it refers to, which can help prevent retain cycles, particularly in closures and when setting up delegate relationships.


Explain what MVC is and how it's implemented in iOS.

MVC stands for Model-View-Controller. It's a software architecture pattern that divides an application into three interconnected components. Models hold the data, Views display the visual elements, and Controllers manage the interaction between Models and Views.


Describe what an Optional is in Swift.

An Optional in Swift represents a variable that can hold either a value or no value at all. It provides a way to handle the absence of a value without the need for checking against nil.


What are protocols in Swift and how are they used?

Protocols are a way of specifying a blueprint of methods, properties, or other requirements for particular tasks. Classes, structs, or enums can then adopt these protocols and provide concrete implementations of the requirements.


Can you tell me what Grand Central Dispatch is?

Grand Central Dispatch is a technology that provides a way to perform concurrent operations in your iOS applications, helping to make better use of the CPU and improve app performance.


What is a storyboard in iOS?

A storyboard is a visual representation of the user interface of an iOS application. It allows developers to layout the flow and transitions between different screens and views.


What is ARC and how does it work?

ARC stands for Automatic Reference Counting. It is a memory management technique in Swift that automatically tracks and manages an app's use of memory by freeing up objects that are no longer needed.


How would you define delegates in iOS?

Delegates are a design pattern that allows one object to delegate responsibility for certain tasks to another object, without needing to know the specifics of how those tasks are implemented.


What is a TableView and how is it used?

A TableView is an iOS user interface element that displays a list of items in a single column. It's commonly used to create menus, lists of options, or any other collection of repeatable content.


What is the difference between 'frame' and 'bounds'?

The 'frame' of a UIView refers to its position and size relative to its superview's coordinate system. The 'bounds' refer to its own coordinate system, starting at (0,0) and including its own size.


Explain KVC and KVO.

KVC stands for Key-Value Coding and it's a way to access an object's properties dynamically using string identifiers. KVO stands for Key-Value Observing and it allows objects to observe changes to specified properties of other objects.


What are enums and when should they be used?

Enums, or enumerations, are a feature of Swift that define common types of related values without spelling out each case. They enhance code clarity and safety when used to
represent a limited set of possible values.

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Describe the difference between synchronous and asynchronous task execution.

Synchronous tasks wait until the task is finished before moving on to the next line of code, while asynchronous tasks can complete in the background and notify you when they're done, allowing the program to continue running other code.


Explain what an escaping closure is in Swift.

An escaping closure is a closure that is passed as an argument to a function but is called after the function returns. It is used for operations that work with asynchronous callbacks, like network requests.


What are generics in Swift and why would you use them?

Generics are a way of writing flexible and reusable code. They allow you to define functions and types with placeholders that can be filled in with any type, reducing duplication and increasing code clarity.


Can you explain what dependency injection is?

Dependency injection is a design pattern that allows a class or structure to be decoupled from its dependencies. It involves providing the dependencies from the outside instead of constructing them within the object.


How do you manage memory in Swift?

Memory is managed automatically through Automatic Reference Counting (ARC). Developers must be mindful of strong reference cycles that can keep objects alive when they should be deallocated. These can be prevented with 'weak' and 'unowned' references.


What's the purpose of the 'guard' keyword?

The 'guard' keyword is used to provide early exit from a function. It's often used for checking validity of conditions and to make code safer and cleaner by handling possible error cases at the beginning of functions.


Explain the use of autolayout in iOS.

Autolayout is a system that allows developers to create a dynamic and flexible user interface that adjusts to different device sizes and orientations by defining constraints that govern the layout.


What is a completion handler?

A completion handler is a type of closure that's passed as an argument into a function and is intended to be called once that function has completed its execution, usually to signal that a long-running task is finished.


Describe how error handling works in Swift.

Error handling in Swift is done using a combination of do-catch, 'try', and 'throw'. Errors can be thrown by functions and caught by 'catch' blocks where you can handle or rethrow them.


Explain what the defer statement is used for.

The defer statement is used to schedule execution of code to just before the current scope exits. It ensures that cleanup or other necessary operations are performed even if an error occurs in the middle of the function.


What is a protocol-oriented programming approach?

Protocol-oriented programming is a paradigm in Swift that encourages the design of software around protocols and their implementations rather than relying on inheritance. It enables more flexible and reusable code.


How does reactive programming differ from traditional programming?

Reactive programming is a declarative programming paradigm concerned with data streams and the propagation of change. It enables developers to build more dynamic applications with data that can automatically update UI when it changes.


What is continuous integration and why is it important?

Continuous integration is a software development practice where developers frequently integrate code into a shared repository. It helps detect issues early and improves the quality of the software.


How do you handle multi-threading in iOS?

Multi-threading in iOS can be handled through APIs like Grand Central Dispatch and NSOperationQueue. These provide a way to perform tasks concurrently to keep the UI responsive while executing background tasks.


What is the Singleton pattern and where would you use it?

The Singleton pattern guarantees that a class has only one instance and provides a global point of access to it. It's useful for managing resources that should be shared across an application, like a network manager.


iOS Interview Tips

Understanding the Question

Before answering an interview question, make sure you understand what's being asked. Listen carefully, and if anything isn't clear, politely ask for clarification. This shows that you're attentive and ensures your answer is relevant. A well-understood question is the foundation of a solid answer. Also, recalling similar past experiences can offer valuable context to your response, demonstrating your practical understanding and how you can apply knowledge to real-world scenarios.

Structuring Your Response

Organize your answer to convey your message clearly. One effective method is the STAR technique (Situation, Task, Action, Result), mainly when discussing experiences. First, outline the situation and the task you faced. Then, describe the actions you took, demonstrating your problem-solving abilities or technical skills. Finally, conclude with the result or outcome. This approach helps in delivering not just what you know, but how you apply your knowledge effectively.

Showing Enthusiasm

Your passion can be as compelling as your technical skills. Express enthusiasm for the role, the company, and the tech stack you'll be working with. Highlight what excites you about iOS development and how you stay up-to-date with the latest updates and industry trends. Enthusiasm often translates to a strong work ethic and can set you apart from other candidates.

Using Examples

Give concrete examples from your past experiences to showcase your competence. Discuss specific projects you've worked on or challenges you've faced and how you resolved them. This not only backs up your technical claims with evidence but also demonstrates your problem-solving process and ability to handle real-world situations.

Communicating Clearly

Clear communication is crucial in an interview. Take a moment before responding to gather your thoughts. Aim for concise, focused answers that directly address the questions. Use technical terms appropriately but avoid overly complex language that might confuse the interviewer. Remember, the goal is to show that you can not only code but also effectively communicate your ideas and work with a team.


How much does it cost to hire an iOS app developer?

The cost for hiring an iOS app developer starts from $45/hour at FireHire, offering competitive rates for top-quality talent. Read more: How much does it cost to hire an iOS app developer?.

How do I hire an iOS app developer?

You can easily hire a developer by reaching out to us at FireHire. Our efficient process quickly connects you with pre-vetted senior-level iOS developers so you can start your project without delay. Read more: How do I hire an iOS app developer?.

How do I find an iOS developer?

With FireHire, finding an iOS developer is effortless. We have a network of over 1600 skilled talents to fulfil any developmental needs your project might have. Read more: How do I find an iOS developer?.

Why using FireHire for hiring iOS developers is the best choice?

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