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How does a senior iOS developer interview other candidates?

In the ever-evolving landscape of mobile app development, iOS stands out for its robust platform, unique design elements, and stringent security features. As a Senior iOS Developer, the mastery over this platform is not just about understanding the syntax of Swift or Objective-C but delving into the intricacies of app architecture, user experience, performance optimization, and security.

These iOS interview questions should hopefully help you be better prepared on what to ask a senior iOS developer.

Ten interview questions

Developing mobile applications is one of the most complex fields in software engineering. Ensure you're not expecting textbook answers but looking forward to open discussion.

1. Explain application architecture

Application architecture and a smart choice of design patterns for a particular use case are pivotal concepts that guide the structural design of apps. It encompasses the organization of code, separation of concerns, and the principles that dictate how different application components interact. A well-thought-out architecture is essential for building scalable, maintainable, and testable applications.

iOS developers commonly employ architectures like MVC (Model-View-Controller), MVVM (Model-View-ViewModel), and VIPER (View, Interactor, Presenter, Entity, Router), each having its unique characteristics. MVC, Apple's recommended pattern, separates an application into three interconnected parts, promoting a clean division of labor. MVVM enhances MVC by adding a ViewModel, facilitating better separation between the user interface and the business logic and easing unit testing. VIPER, a more complex architecture, breaks the app into more distinct components, fostering better organization in large applications but at the cost of increased complexity.

The choice of architecture depends on various factors, such as the size and complexity of the engagement , team preferences, and specific engagement requirements. A senior iOS developer must be adept at implementing these patterns and possess the discernment to choose the most appropriate architecture for each project.

2. How would you define concurrency and multithreading in iOS, and how do they work?

Concurrency and multithreading are crucial concepts in iOS development, particularly in the context of Swift. They enable apps to perform multiple tasks simultaneously, improving performance and responsiveness. Swift provides several tools and APIs for managing concurrency and threading, such as Grand Central Dispatch (GCD) and Operation Queues.

GCD is a low-level API for managing concurrent tasks. It allows developers to execute operations concurrently or serially on different queues. GCD is beneficial for performing tasks that don't need to run on the main thread, like fetching data from the internet or a database.

Operation Queues, on the other hand, are higher-level abstractions. They use GCD internally but provide more control and flexibility. Operations can be canceled, dependencies can be set between them, and their execution can be observed.

A senior iOS developer should have a solid grasp of these concepts and be able to apply them effectively in Swift. This includes understanding how to avoid common issues like race conditions, deadlocks, and priority inversions, ensuring the app remains efficient and responsive.

3. What is your understanding of memory management and performance optimizations?

In iOS development, memory management and performance optimization are interlinked with Xcode, offering powerful tools to aid in these areas.

Memory Management: Swift uses Automatic Reference Counting (ARC). It automatically keeps track of an object's references and deallocates it when the reference count drops to zero. Senior iOS developers must handle strong, weak, and unowned references to prevent memory leaks and retain cycles.

Performance Optimizations: Key performance areas in iOS apps include responsiveness, resource utilization, and battery efficiency. Developers should optimize CPU usage, memory usage, and disk I/O operations. Techniques like lazy loading, caching, and efficient data structures play a vital role.

Xcode Tools: Xcode provides various built-in tools for profiling and optimizing iOS apps. Instruments, a part of Xcode, are instrumental in identifying performance bottlenecks, memory leaks, and resource usage. It offers a range of profiling templates like Time Profiler, Allocations, Leaks, and Energy Diagnostics. These tools allow developers to monitor and optimize various aspects of the app during different stages of the development cycle.

An experienced iOS developer should be proficient in leveraging these tools to ensure the app performs optimally under various conditions and device capabilities.

4. What are some security best practices?

Security best practices in iOS development encompass a range of strategies to safeguard data and user privacy. Key practices include:

Data encryption: Encrypt sensitive data in transit and at rest. Utilize SSL/TLS for network communication and strong encryption methods for storing data locally.

Code hardening and obfuscation: Protect against reverse engineering by hardening and obfuscating the code.

Secure authentication: Implement robust authentication mechanisms. Use OAuth, biometrics, and token-based authentication where applicable.

Regular updates and patching: Keep the app and its libraries up-to-date with the latest security patches.

Least privilege principle: Limit the app's access to system resources and user data to only what is necessary.

Validating user input: Prevent injection attacks by validating and sanitizing user inputs.

Utilizing keychain services: Store sensitive information like passwords and tokens in the iOS Keychain.

Each practice plays a vital role in building a secure iOS application.

5. How do you handle dependencies in an iOS project?

Handling dependencies in an iOS project is a critical aspect of modern iOS development. It involves managing external libraries and frameworks that your app relies on. The primary methods for dependency management in iOS are:

CocoaPods: A widely-used dependency manager for Swift and Objective-C engagements. It simplifies the process of integrating and updating third-party libraries. Swift Package Manager (SPM): Apple's official tool for managing Swift code dependencies, integrated directly with Xcode.

Each tool has its strengths and is chosen based on project requirements, team preferences, and ease of use. A senior iOS developer should be proficient in using these tools, understanding their pros and cons, and managing dependencies efficiently to ensure smooth project maintenance and scalability.

6. Explain state management and its importance in the application lifecycle.

In iOS, particularly with SwiftUI, state management is pivotal for updating the user interface dynamically in response to underlying data changes. SwiftUI provides property wrappers like @State, @Binding, @ObservedObject, and @EnvironmentObject to manage the state declaratively. These wrappers help create a source of truth for the data and enable seamless communication between the data and the UI components.

As for the application lifecycle in SwiftUI, it is managed through the @main attribute, which denotes the app's entry point; SwiftUI introduces a new lifecycle that relies on App and Scene protocols to manage the app's states like active, inactive, and background. This approach is a shift from the traditional UIKit lifecycle methods, offering a more streamlined and efficient way to handle state transitions and lifecycle events in an iOS application.

In UIKit, the application lifecycle is managed through a series of methods in the UIApplicationDelegate protocol. Understanding and correctly implementing these methods is crucial for managing resources, saving state, and ensuring smooth transitions between different states in a UIKit-based iOS app.

7. Why are testing and continuous integration vital, and what do they encompass?

Testing and Continuous Integration (CI) are integral to ensuring the quality and reliability of iOS applications. Testing involves unit tests, UI tests, and integration tests. Unit tests verify the smallest parts of an application, UI tests automate user interaction with the app, and integration tests ensure that various parts of the application work well together.

Continuous Integration is a development practice where developers frequently integrate their code into a shared repository. Tools like Jenkins, Travis CI, and Xcode Server automate the process of building and testing the app every time a change is made, helping to catch issues early. Effective use of CI/CD pipelines ensures that the app remains stable and deployable throughout its development lifecycle.

8. Discuss your experience working with device integration, such as HomeKit.

Working with device integration in iOS, especially with frameworks like HomeKit, involves interfacing with various smart home devices. HomeKit allows for the secure and seamless integration of home automation products with iOS apps. As a developer, this entails understanding HomeKit's architecture, which includes managing and communicating with accessories, creating actions and triggers, and ensuring user privacy and security. Proficiency in HomeKit also requires staying updated with the latest advancements in IoT and smart home technologies and understanding the unique challenges posed by device interoperability and network reliability.

9. What is your experience working with SwiftUI and UIKit?

Working with SwiftUI and UIKit offers distinct experiences in iOS development. SwiftUI, Apple's latest UI toolkit, enables a declarative syntax and a unified approach to UI development across all Apple platforms. It simplifies building complex user interfaces with less code and offers live previews. However, as it's relatively new, it sometimes requires fallbacks to UIKit for specific functionalities.

UIKit, on the other hand, is the original UI framework for iOS. It provides a comprehensive set of tools and controls for building iOS interfaces. While it requires more boilerplate code compared to SwiftUI, it offers greater control and is currently more comprehensive regarding supported functionalities. Experienced iOS developers often work with both, leveraging the strengths of each according to project needs.

Note: The developer does not have to answer as we have. It’s important that they mention what their experience has been like. Keep an open mind with this question.

10. Discuss your experience working with device hardware, maps, etc.

Working with device hardware and Apple Maps in iOS development involves leveraging the rich capabilities of Apple devices. Integrating device hardware, like the camera, accelerometer, or GPS, requires a deep understanding of the respective APIs and frameworks, ensuring seamless and efficient usage. Working with Apple Maps involves integrating map features into apps, utilizing APIs for location tracking, and route planning, and providing interactive map experiences. These integrations enhance the app's functionality, offering users a richer, more interactive experience.

Note: Ensure the developer provides examples of what working with device hardware, maps, etc., has been like for them.


Whether you are a seasoned iOS developer or new to the field, becoming a senior developer is one of lifelong learning and adaptation. Choosing either Swift or Objective-C as a primary programming language can have a giant impact on the trajectory of one's career and potential future job prospects.

Due to Apple's innovation and the users' demand for high-quality experience, it's crucial that a professional in the field stays up to date with the latest trends and technologies, connects with others, and puts the creation of people-centric, impactful applications to the forefront. As developers, we are tasked with not only coding but also pushing the boundaries of what incredible experience can be and what our applications can achieve. The days of mobile application development being solely software development focused are over. Nowadays, the expectations from individuals or single development teams are far more significant.

As iOS continues to evolve, so will the opportunities and challenges.

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