iOS Engineer Interview

Interview Guide Dec 02

Detailed, specific guidance on the iOS Engineer interview process - with a breakdown of different stages and interview questions asked at each stage

The role of iOS Engineer

iOS Engineers are integral to the development of applications, impacting millions of users daily. Their role involves designing, building, and maintaining mobile applications to meet both user needs and technical specifications. The significance of their role is evident in preventing malfunctions and ensuring proper updates for Apple mobile devices.

Given the sustained popularity of Apple devices and the thriving App Store ecosystem, the demand for iOS Engineers is robust. The US Bureau of Labor Statistics anticipates a 25 percent growth in demand for iOS developers from 2021 to 2031.

For those considering a career in iOS development, the compensation is attractive, with the average total package for an iOS Engineer standing at a competitive $134,878.

iOS Engineer Interview Guide

While the specific interview process at different companies will vary, the iOS Engineer role typically comprises the following 3 rounds of interviews:

  • Phone Screen
  • Technical Screen
  • Onsite

Occasionally, there may be a take-home assignment which typically involves solving domain-specific questions related to developing a relevant iOS application. However, such assignments are becoming increasingly uncommon. Whatever the case, your recruiter will inform you.

Let's discuss the interview process in detail:

Relevant Guides

iOS Engineer - Phone Screen with Recruiter

Overview

To kick things off, you'll likely have a chat with the hiring manager or recruiter, or sometimes both. The call often starts with a brief introduction from both sides; the hiring manager might introduce themselves and their role within the company, and you'll have the opportunity to briefly introduce yourself. This interview is generally a relaxed and informal conversation—the goal here is to understand you better. 

Beyond that, expect some basic iOS questions – Core Data, UIKit, App Store submission process, you know the drill. They might dig into your experience with iOS frameworks, tools, and best practices. If you have a second phone screen with an HR, they'll toss in some character-based questions and circle back to your tech skills in iOS. 

These interviews are usually not too challenging to pass. Ensure you have a concise elevator pitch, have reviewed iOS fundamentals & your previous work experiences, and most importantly, have a compelling answer for why you're interested in joining that particular company. 

Be sure to discuss your relevant experiences and tie them with the said company's values.

iOS Engineer - Technical Phone Interview

Overview

This is a more in-depth call where you speak with an Engineer from Tinder who will likely ask you a bunch of coding and technical questions. The aim is to evaluate your technical and problem-solving abilities related to iOS development. 

The contents of the interview vary for different companies. For instance, Google places significant emphasis on Swift, even if your prior experience is primarily in Objective-C. The reason for this is to assess your ability to quickly adapt to new technologies and still deliver a high-quality project—which is a must-have skill at Google.

At Meta, the bulk of the technical screen is dedicated to coding problems. One thing is common for all iOS engineer tech screens: the coding problems aren't typically iOS-specific—and instead tend to focus heavily on computer science fundamentals. They revolve around basic data structures and algorithms. You can also expect theoretical questions like "Frames vs Bounds?" or "what is MVVM-bindings?”

A great way to prepare for the technical phone interview as an iOS Engineer is to practice with mock interviews, especially with experienced iOS Engineers. You can find such experts from top companies like Google, Meta, Tinder on platforms like Prepfully, where you can book 1:1 sessions directly with them.

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iOS Engineer - Onsite Interview

Overview

During the onsite interview, you typically have 4 or 5 interviews over the course of the day. These will be distributed across 4 different types of interviews: iOS Knowledge Interview, Coding Interview, iOS Design Interview, and Behavioral Interview.

  • iOS Knowledge Interview: These are often based on practical scenarios you might encounter in your day-to-day work. Expect questions related to iOS development, such as how to use essential APIs, how memory management works in iOS, and so on. 
  • Coding Rounds: These typically focus on evaluating your problem-solving skills and understanding of fundamental concepts in context to iOS app development. You may be given multiple technical questions which revolve around analyzing algorithmic complexity and applying data structures effectively. You will be asked to write code on a whiteboard and explain your solution. So, brush up on essential data structures like arrays, linked lists, stacks, queues, and trees. Understand their properties, operations, and time/space complexities. Familiarize yourself with common algorithms like sorting, searching, and graph traversal. Practice implementing these data structures and algorithms in Swift. Some companies also ask you to solve domain-specific problems related to iOS development— be prepared for those as well. 
  • iOS Design: This round is typically present if you're interviewing for a senior-level position. You won't be expected to write code for this, but you'll need to design a reasonably complex system.  For instance, “design a system for a real-time chat application on iOS.” It’s important to note - the iOS Design interview is a bit different from traditional “backend focused” system design. The interview you’ll face will be much more app-focused than back-end focused so it’s worth investing into preparing for them. Your interviewer is trying to understand your ability to solve a complicated iOS engineering design problem. Or in other words - can you architect a high-level solution to a problem that has multiple concepts and components. Have a structure and methodical approach. Our general recommendation is to split things into discrete layers starting from the View, Controller, Network, Storage, Cache, since this is how you’d design a system in real life. 
  • Behavioral Round: This is where they get to know you better as a candidate. They may inquire about your previous experiences, your problem-solving approach within the realm of iOS development, and evaluate your communication abilities. To ace this round, it's important to connect your answers to past experiences and emphasize on the values & culture of the company you’re applying to. Provide specific, concrete examples of times you've displayed excellent collaboration skills, communication skills, etc—essentially traits that company’s value in iOS engineers.

Preparation is key here, for both the design as well as coding rounds—which can get progressively challenging. So, we'd recommend you seek practice sessions with professionals, such as the 18 iOS Engineers available on Prepfully. They possess valuable insights into common mistakes to avoid and can offer guidance on improving your interview performance. Book a 1:1 session with them directly here.

Interview Questions

Interview Questions:

  • You're tasked with designing a weather app for iOS. Describe the components, data sources, and user interface elements you would include, and explain the architectural pattern (e.g., MVC, MVVM) you'd use to build it.
  • How does URLSession differ from NSURLConnection in iOS? Describe the key features and advantages of URLSession, and when you would choose one over the other.
  • Explain the concept of Grand Central Dispatch (GCD) and when you would use it in an iOS application.
  • Given an array of integers, find the longest increasing subsequence. Explain the time and space complexity of your solution.
  • Define and explain the concept of the responder chain in the context of iOS development.
  • Elaborate on the differences between Grand Central Dispatch (GCD) and Operation Queues in managing concurrent tasks in iOS development.
  • What are the drawbacks of using storyboards?Explain the difference between protocols and inheritance.
  • Highlight the distinctions between structs and classes.
  • Discuss the concept of mutating methods in both structs and classes.
  • Elaborate on the differences between unowned and weak references.
  • Provide an example to illustrate the concept of a retain cycle in memory management.
  • Share the disadvantages of using the Singleton design pattern.
  • Find the common parent of two UIViews in a view hierarchy.
  • How would you design the data flow and storage mechanisms within an iOS app, considering factors like network requests, local caching, and data persistence?
  • Explain your approach to designing the user interface (UI) of X iOS app. How would you ensure a seamless and user-friendly experience?
  • Given two views, write an algorithm to find the closest common superview if one exists.
  • How would you design a flight booking app?
  • Implement a hashmap data structure.
  • Design an airline booking app.
  • Describe a time when you had to resolve a dispute with a teammate.
  • How many ways can you implement concurrency in iOS?
  • What is the difference between OperationQueue and GCD?

iOS Engineer Roles and Responsibilities

Following are the roles and responsibilities of an iOS Engineer:

  • You'll write code for building products or systems. You'll carefully check the code created by other engineers and provide helpful feedback to ensure it follows the right coding rules, is correct, can be tested, and runs efficiently.
  • You'll work closely with product and design teams. This means you'll be actively involved in shaping and implementing innovative application experiences for the iOS platform.
  • Another important aspect of the role is building reusable iOS software components. These components should be designed to interact with back-end platforms efficiently.
  • Efficiency matters, and you'll be tasked with analyzing and optimizing both the UI and infrastructure application code. Expect to dive deep into performance optimization.
  • You'll extend and implement APIs, which are essential for the app's functionality. This includes integrating with backend systems and ensuring data flows securely and efficiently.
  • You'll be responsible for implementing unit tests to ensure that your code is reliable and functions as expected.
  • You need to stay up-to-date with industry standards, best practices, and the latest tools and technologies in iOS development.

iOS Engineer Skills and Qualifications

Here are the skills and qualifications that an iOS Engineer must have:

  • A MInimum of a Bachelor's, Master's, or Doctorate (Ph.D.) degree in Computer Science or an equivalent field is required. Proficiency in modern iOS technologies and principles, iOS memory management and protocol-oriented programming is key.
  • You will be expected to have at least 3-5 years of experience building consumer-facing applications with native iOS.
  • You should have 2 years of experience dealing with data structures or algorithms, either in school or in a tech job.
  • Proficiency in Objective-C, C++, or Swift, along with a deep understanding of the iOS SDK and other relevant frameworks, is essential.
  • Sound knowledge of systems architecture and object-oriented programming concepts. 
  • Proven experience in the complete app development lifecycle, including building, launching, and iterative improvements on mobile apps.

Frequently Asked Questions