The iOS App Store offers more than 1.87 million applications, making it one of the leading mobile application vendors across the globe. It currently holds 14.1% of the market share of smartphone shipments, which is indicative of how popular iOS development is.
For businesses, a mobile application can significantly increase brand awareness, enhance customer engagement, and act as an effective marketing channel. When 42% of small businesses have an app, not having a mobile app for your company can put you at a disadvantage compared to the rest of the market. Thus, to strengthen your business with a reliable application, you need to find a capable developer.
With 26.9 million software developers worldwide, hiring the right iOS developer can be a daunting experience. Even worse, you could end up investing in a resource that fails to deliver as per your expectations. Furthermore, iOS developers hail from a highly diverse set of backgrounds today. From graduates of prestigious academic institutes to individuals without any degrees, there are too many players in the field.
In order to gauge everyone on a fair scale, it is important to know what iOS development entails, the skills an iOS developer should ideally possess, and the factors to take into account when making your final choice.
Native iOS vs. cross-platform iOS development
When considering an iOS-powered mobile application, it is necessary to determine the type of development that will be the most suitable for your specific use case. This decision will have long-term implications when it comes to cost, functionality, and performance.
The two types of development for iOS are native and cross-platform development.
Native iOS development
This type of development refers to building a product exclusively for a single platform – in this case, iOS. This means that the application will be built using the official programming tools and languages for iOS. There are two native languages for this operating system: Objective-C and Swift. An application built with these will only function on the iOS platform.
Cross-platform iOS development
As the name suggests, cross-platform development creates applications that can function on multiple platforms. This includes the use of such tools as React Native and Flutter since applications created with them can be deployed on Android, Windows, and iOS platforms. Such applications have a single codebase and usually offer faster development.
That being said, native application development is often preferred by developers since it offers broad functionality, increased scalability, better use of device-specific features, high performance, and an excellent user experience. Hence, we will be focusing on native iOS development within the framework of this article.
Native iOS developer responsibilities
An iOS developer is responsible for creating and architecting applications for mobile devices powered by iOS, Apple’s operating system. The exact set of responsibilities would vary as per the team size, experience, project complexity, and work dynamics. However, there are certain responsibilities that are expected from all developers working with iOS:
- Writing code in Swift and Objective-C;
- Developing user interfaces;
- Ensuring quality of the application;
- Collaborating with the design team to define app features;
- Writing and performing unit and user integration tests;
- Identifying and resolving errors;
- Implementing application updates.
While larger companies might have dedicated resources or even teams for each task, smaller places usually have developers performing all these duties.
Skills for a native iOS developer
Before hiring an iOS developer, make sure that you are aware of the exact job description and the competency required for the role you are offering. It is important that the candidate fits well with the kind of project(s) you have in mind, no matter how competent they might seem otherwise.
Must-have technical skills for iOS developers
Some of the most crucial skills of an iOS developer include the following:
- Proficiency in Swift programming language, particularly its syntax, Objective-C interoperability, inheritance, and initialization;
- Strong command of UI and UX design in mobile application building;
- Proficiency in using code versioning tools that allow collaboration on small to large projects with speed and efficiency;
- Deep understanding of Apple Human Interface Guidelines to develop apps that conform to Apple’s minimalistic and elegant style;
- Full comprehension of JSON for networking;
- Knowledge of Core Data and how it persists storage in an Apple device;
- Awareness of technical aspects and concepts, such as concurrency, reactive programming, and animations, etc.
iOS Component libraries every mobile developer needs to know
The most promising candidates would be proficient with multiple iOS libraries. Some of the most popular iOS libraries that professionals vouch for include the following:
- Eureka – an open-source form building library that makes UI code less repetitive and complex;
- Kingfisher – a lightweight, pure-Swift library for downloading and networking cached images;
- Alamofire – HTTP networking library for abstracting away and simplifying networking;
- ObjectMapper – a class that converts a JSON response into a model object and vice versa;
- Material Motion – a reactive animation library for creating composable animations;
- SwiftLint – a tool for enforcing Swift style and conventions;
- SnapKit – an auto-layout library for simplifying the writing of auto layout code;
- Hero – a library for building iOS view controller transitions.
As is prevalent in development, different problems require different libraries. It is not uncommon that a relatively lesser-known library outperforms a popular one for a particular issue. Therefore, beyond having a strong command over the aforementioned libraries, it is important to be willing and capable of learning and implementing new libraries in a short time.
Soft skills for iOS developers
A developer needs to be an enthusiastic learner and be able to pick up new skills and information very fast. This is because the advancements in the world of development are rapid, and keeping up with them is the only way to stay proficient in them.
Moreover, the ideal candidate should be able to perform their tasks as expected within the agreed timeframe. If the task is not going well, they should be able to communicate it with the team and prolong the deadline, ask for help, revisit the task specification, etc.
How to interview iOS developers
While a resume or CV shows the credentials of the applicant, the numbers and honors listed there do not give a fully comprehensive overview. For instance, it is important to know how a person approaches a tricky problem, how strong and conceptual their technical knowledge is, or how innovative their solutions are. This information can be gained from a well-devised interview.
Here are a few sample questions, categorized according to different levels of experience, that can help evaluate a candidate.
Junior iOS developer interview questions
For junior developers, interview questions should cover the basics of programming as well as iOS development. It is better to ask questions with multiple correct solutions. Furthermore, these questions could cover basic knowledge of programming concepts and salient features of languages. The focus here should be on data structures and algorithms related to iOS development.
Q1. What is the difference between static typing and dynamic typing?
A1. Static typing can give you a compile error, whereas dynamic typing performs type checking at runtime. This allows the code to compile even if it contains error(s) that can prevent it from running. Knowing that Swift uses static typing and Objective-C uses dynamic typing is also expected.
Q2. Can objects be nil/null in Swift and Objective-C?
A2. Only optionals can be null in Swift, but in Objective-C, any object can be nil.
Q3. What is the difference between let and var in Swift?
A3. Let and var are used for creating variables. It should be mentioned that let creates immutable variables that are essentially constants, whereas var creates mutable variables. Additional points for elaborating that when creating a constant using let, it has to be assigned a value first before it can be used and that this assignment cannot be changed later.
Q4. How many states are there in the iOS app lifecycle, and what are they?
A4. There are 5 states in the iOS app lifecycle.
- Not running: When the app is not yet launched by the user or is terminated by the system, it is in the not running state.
- Inactive: The app remains in this state briefly during the transition between different states.
- Active: This is the normal state of the app when it is in the foreground and is receiving user events.
- Background: When the user taps on the home screen while using the app, it goes into this state. This state can also occur right before an app goes into the suspended state.
- Suspended: The app is in the background and does not execute any code in this state. Although it is in the memory, it can be removed at any time since apps in the foreground have a higher priority.
Middle iOS developer interview questions
In order to answer challenging questions, middle-level iOS developers would have built real projects and applications and thus, would ideally be incorporating anecdotes in their explanations. They can be asked abstract questions or tested on the depth of their knowledge regarding common iOS topics.
Q1. What is the latest version of iOS that you have worked with, and what is your review of it?
A1. This question is meant to check whether the candidate keeps up with the latest developments and releases in iOS. A strong answer will be able to highlight specific features from the iOS and discuss their merits or demerits in comparison with previous versions of iOS.
Q2. When is it suitable to use Core Data over NSUserDefaults?
A2. When storing a large list of elements, Core Data should be used. Otherwise, for small pieces of data, such as preferences, NSUserDefaults is preferable.
Q3. How do you usually persist data on iOS?
A3. There is no 100% right answer to this question because it all comes down to the requirements of the project. However, a developer who has significant experience working with iOS would be able to discuss more than one data persistence mechanism, even if they prefer a particular method. These can include UserDefaults, SQLite, Property List, Keychain, Saving files, and Core Data.
Q4. How do you debug or profile code on iOS?
A4. While there is no correct or standard solution for this, expected answers include information regarding NSLogging and printing in iOS. The mention of setting breakpoints using XCode is also appreciable. XCTest’s measure block could also be mentioned if the performance evaluation of code is brought up.
Senior iOS developer interview questions
Senior developers don’t need to be quizzed on typical topics or asked about specific methods or lifecycles. Instead, their interview should be more abstract and open-ended and focus more on the business requirements. Questions should be designed to assess how much knowledge and technical skills the interviewee has gained in their years of experience.
Q1. What mechanisms are provided by iOS to support multi-threading?
A1. The answer should include the two main APIs used for implementing multi-threading: Grand Central Dispatch (GCD) and Operation. Besides this, an explanation of what happens behind the scenes is also expected. The concept of thread pool should be explained with clarity that the APIs manage a large number of threads and grab a thread from the pool when a task is to be executed.
Q2. Explain your process for tracing and fixing a memory leak.
A2. The answer will offer information about the candidate’s knowledge of memory, instruments, and debugging process. There can be multiple ways for this, some very creative. However, something as trivial as commenting code until the problematic part is identified is a red flag.
Q3. We face issues with memory management. How would you handle it on iOS?
A3. The interviewee should understand directives, such as strong, weak, and assign, and know their implications. It is a plus point if they know Manual Retain Count (MRC). The answer to this question will tell how long the candidate has actually worked with iOS and how proficient they are with memory management in iOS.
Q4. How should we increase the security of our app?
A4. Some of the most significant methods for implementing security in iOS should be mentioned, for instance, SSL cert pinning, jailbreak detection, storing info in a keychain, file data protection, and third-party library usage, etc.
There are multiple challenges offered online that test the practical skills of a developer with different coding tasks. However, to overcome some of them, the project might require tricky solutions that are almost never used in real projects.
An ideal coding challenge should look like any task for your project. It can be making a new page, designing a module, writing a class or two, or a simple application – all depending on the expected seniority level. It can be a good idea to give the developer a task to take home that is about 2-4 hours’ worth of work and then review it in detail as part of a technical interview. This way, a candidate will be able to justify their solution, explain their way of thinking, and show their expertise from different angles.
How much does it cost to hire iOS developers
Once you know how to hire iOS developers, the only remaining concern is the cost. The rates for iOS developers can vary largely, depending on their experience as well as the region they belong to.
The following rates have been compiled from sources, such as SalaryExpert and Payscale, and are the average salary in USD.
You can also employ a cooperation model to easily determine where to find an iOS developer that suits your requirements and is within your budget.
With a multitude of factors to consider when selecting an iOS developer, it can largely simplify your choice and streamline the hiring process if you know exactly how to gauge a candidate. The choice of your iOS developer does not only impact how your resources are used but also directly affects your business performance.
Thus, make sure you are well aware of the type of developer you want, what skills and technical knowledge you require from them, and what questions you want to ask to double-check if they meet your expectations.