iOS developers are in high demand, and because over a billion active Apple devices are in use worldwide, the demand is likely to continue growing. If your company intends to hire an iOS developer, you will likely find yourself conducting multiple interviews. However, human resources professionals who conduct initial job screenings may lack familiarity with the ins and outs of this role.
This guide includes essential iOS developer interview questions for junior-, mid-, and senior-level iOS developers. Familiarize your recruitment team with these questions and sample answers to effectively conduct initial interviews and advance the most qualified candidates through selection.
Allocate plenty of time to ask these key interview questions for iOS developers. Being thorough during this process is the best way to ensure you end up with your ideal hire.
What Is an iOS Developer?
An iOS developer is a mobile app developer responsible for designing and creating applications that operate on Apple's iOS devices. To excel in this role, the iOS developer must possess expertise in two programming languages: Objective-C and Swift.
The key responsibilities of most iOS developers include the following:
- Coding iOS applications in a clean and efficient manner
- Identifying and resolving issues and bugs in applications to ensure clean and secure code
- Developing and implementing advanced app features while maintaining and enhancing existing features
- Devising innovative solutions to meet a company’s requirements
- Assisting in all stages of application development, including design, testing, release, and support
- Continuously exploring, assessing, and adopting new technologies to enhance development efficiency
Entry-Level iOS Developer Interview Questions
After you have assessed a candidate's general familiarity with fundamental iOS concepts, you can proceed to tailor questions according to their level of expertise. Below, we’ve included typical, entry-level technical questions and responses for an iOS interview with candidates possessing minimal practical experience.
Break down the iOS architecture and explain each layer in detail.
iOS follows a layered structure composed of four distinct layers that provide a programming framework for app development on the hardware platform. Communication is facilitated between the application layer and the hardware layer. An upper-level layer, also known as a high-level layer, provides graphics and interface-related services; a lower-level layer provides the services that all apps need.
The four layers are as follows:
- The core OS (or application) layer resides directly above the hardware and forms the foundation of the iPhone OS stack. It offers essential operating system services such as memory management, file system handling, and thread management. Additionally, this layer provides low-level networking capabilities and access to external accessories.
- The service layer is responsible for fulfilling the demands of the upper layers and users. It encompasses features like block objects, a low-level API for managing concurrent operations called Grand Central Dispatch (GCD), in-app purchases, and iCloud storage. The introduction of Automatic Reference Counting (ARC) has further bolstered the capabilities of the service layer.
- The media layer handles media-related functionalities like video, audio, and graphics.
- The cocoa touch layer, or application layer, is where frameworks are made when apps are built. It acts as the interface through which iOS users interact with the operating system, encompassing touch and motion capabilities. The cocoa touch layer is vital, providing an intuitive and user-friendly experience.
What framework is used to develop the user interface of iOS applications?
Unlike the foundation framework encompassing protocols, classes, and functions for both iOS and macOS development, UIKit focuses specifically on iOS development. It is the foundation for constructing the user interface and graphical infrastructure of iOS applications. Some of the features offered by UIKit include the following:
- Event handling: Enables the handling of various gestures, such as input gestures, button taps, and multi-touch gestures
- App structure: Manages the interaction between the user and the system, ensuring smooth navigation and operation within the application
- User interface: Provides a wide range of user interactions, allowing users to share text and content, select images, edit videos, and print files
- Graphics, drawing, and printing: Supports graphical elements and allows for drawing on the screen, rendering images, and facilitating printing capabilities
- Cut, copy, and paste: Supports this functionality within the application
- Accessibility: Supports access for users with disabilities
What are app IDs and bundle IDs, and how are they used?
Bundle IDs serve as the unique identifiers for applications within Apple's ecosystem, ensuring that no two apps share the same identifier. They are used for both OS X and iOS apps and aid in recognizing app updates.
An app ID is a string uniquely identifying one or more apps the same team has developed. It contains two components: the team ID and the bundle ID. Apple assigns a team ID to every development team, while developers assign bundle IDs to differentiate individual apps or a collection of apps.
Mid-Level iOS Developer Interview Questions
To hire iOS app developers at the mid-level, you’ll want to ask more advanced questions that show a higher level of expertise. Let’s explore three of those now.
What does "concurrency" in iOS mean, and how do you achieve it?
“Concurrency” refers to running more than one task at the same time. There are three primary methods used to achieve concurrency in iOS:
- Dispatch queues: These manage tasks in a first-in-first-out (FIFO) order, enabling sequential or concurrent execution of tasks. They provide a convenient approach for handling asynchronous and concurrent tasks within your application.
- Threads: These allow the execution of independent sequences of instructions separately from other codes within a program. They enable the simultaneous execution of multiple code paths within a single application. Threads are particularly valuable when you need to perform lengthy tasks without impacting the rest of the program’s execution.
- Operation queues: These function according to priority and act as high-level abstractions of queueing models built on top of GCD. As with GCD, operation queues allow concurrent task execution but with an object-oriented approach.
What are the major features of the Swift programming language?
If you’re looking to hire Swift developers, Swift’s main features include the following:
- Safety: Swift eliminates unsafe code before it goes into production.
- Simple syntax: Swift is easy to use due to its simplicity.
- Multiplatform support: Swift lets you develop apps that work with all operating systems because it’s compatible with iOS, macOS, watchOS, tvOS, Linux, and other platforms.
- Readability: Swift’s simple syntax makes it easier for developers to read, allowing them to spend less time searching for bad code.
- Open source: Swift’s non-closed nature makes programming with it faster, easier, and safer.
- Compatible with Objective-C: Swift’s full compatibility with Objective-C means that developers can use Swift to import frameworks from Objective-C and use Objective-C classes and libraries within Swift code.
- Dynamic libraries: Swift supports dynamic libraries (executable pieces of code that you can connect to an app) that are directly uploaded, ultimately enhancing app performance.
Explain the importance of design patterns and the different types.
Design patterns solve specific problems encountered during the app architecture design process. They serve as templates that enhance code reusability and simplify coding.
Here are a few design patterns in iOS:
- MVC (Model-View-Controller): This design pattern lets you develop web apps in which the model, view, and controller are connected. The model represents the data, the view is the user interface, and the controller links the model and view.
- MVVM (Model-View-Viewmodel): This allows model information to transform into values the view can display.
- Facade: This allows for a simplified interface for a complex set of libraries, frameworks, or classes, which reduces app complexity.
Senior-Level iOS Developer Interview Questions
Senior iOS developer interview questions should separate new developers from experts, so you’ll want to scrutinize candidates’ skills and knowledge to determine whether they’ll do well in a job. Below are three questions to ask.
What is the test-driven development (TDD) process?
TDD involves strategic planning of software features and creating corresponding test cases before implementation. This approach evaluates implementation quality (functionality) and design quality (structure).
Initially, the test case will fail because the developer hasn't implemented the code. Then, the developer will write code to ensure the test case passes. Next, the developer will refactor the code's implementation.
How do synchronous and asynchronous tasks differ?
Synchronous operations handle tasks individually, causing other tasks to wait until the previous one finishes. Alternatively, asynchronous tasks run simultaneously in the background. Notifications are sent once background tasks are completed.
By leveraging asynchronous programming, you can handle multiple requests concurrently, enabling the completion of more tasks in a shorter timeframe.
Name the programming languages used in iOS application development.
iOS developers use the following programming languages to develop apps:
Hire iOS Developers With Revelo
Whether you employ an HR team for candidate screening or conduct interviews yourself, it is essential to have a standardized set of questions to ask potential hires. Although the conversation may diverge, maintaining consistency in your questions facilitates better candidate comparisons.
If you lack the time, resources, or technical expertise to source, vet, and onboard candidates, Revelo can help. We can save your company valuable time and effort by connecting you with our highly qualified, rigorously vetted, Latin America-based talent network. After you select your ideal hire from our shortlist, we handle the rest, from payroll and benefits administration to taxes and local compliance, so you can focus on growing your business. Contact Revelo today to get started building your development team.