CodeSubmit Interview Series

The 7 Best iOS Developer Interview Questions in 2023

Looking for the best iOS developer interview questions? Here’s what you need to know about the top interview questions to ask at your next interview.

Want to learn more? Read on!

Interviewing iOS developers 

An iOS developer is a mobile developer with an in-depth understanding of the iOS ecosystem and how to customize apps for the iOS ecosystem. iOS developers are familiar with Swift and often also Objective-C. They work with all the parts of the iOS ecosystem; iPhones, iPads, Apple-TV, and more. 

But how do you identify the best iOS developers? Start with these interview questions: 

Beginner iOS developer interview questions

What are the top junior iOS developer questions? These are the top interview questions to ask beginner developers. 

1. What does the iOS architecture look like? 


The iOS architecture builds on four layers. Each layer offers a programming framework for applications that work on top of the hardware. The upper-level layers provide graphics and interface-related services, while the lower-level layers provide the services that all applications will require. The layers between the Application and the Hardware layers enhance communication. 

The different layers are: 

  • Core OS/Application Layer: The Core OS Layer is the lowest-level layer and sits on top of the device hardware. This layer manages memory, file systems, and thread, as well as low-level networking, access to external accessories, and so on. 

  • Service Layer: The Service Layer designs the services that upper layers and users demand. This layer blocks objects, Grand Central Dispatch, in-app purchases, and iCloud storage. 

  • Media Layer: The Media Layer handles and enables media like video, audio, and graphics.  

  • Cocoa Touch Layer: This is the application layer where you create frameworks. It also works as the interface for iOS users to work with the operating system. 

2. Define Swift and Objective-C.


Swift is the programming language for iOS built by Apple that builds on C and Objective-C. It’s built to offer as much freedom as possible to developers. It’s relatively easy to use and open source.

Objective-C used to be the primary programming language for iOS until Swift was introduced. It’s a superset of C. It provides object-oriented capabilities and a dynamic runtime as well as the syntax for defining classes and methods and language-level support for object graph management and object literals while it provides dynamic typing and binding with many responsibilities deferred until runtime. 

3. Explain the different types of iOS application states. 


The iOS application goes through several stats during execution and each state is known as a lifecycle state. These are:

  • Not running: In this state, the application hasn’t been launched or it’s been closed or shut down by the system. 

  • Inactive: The app is briefly inactive when it’s leaving or entering the active state as it isn’t ready to accept user input or events. 

  • Active: The app is running in the foreground and is receiving events. This is typically the normal mode for foreground apps and the User Interface is accessible. 

  • Background: The application’s interface is hidden but it continues to run in the background. Applications typically go through this state before they’re suspended. 

  • Suspended: the application isn’t running code while it’s in the background. 

4. Explain process and thread in iOS development and their differences. 


Processes and threads help you manage your app’s interaction with the host operating system and other processes, as well as implement low-level concurrency features. 

A process is a heavy-weight process and a separate program with its own memory, data, resources, and so on. Processes are created with the fork() method. For instance, a process starts whenever a new browser is opened.

A thread is a lightweight process that is bundled inside the process. They share memory, data, resources, and so on and are created using the clone() method. 

Advanced iOS developer interview questions

What are the best senior iOS developer interview questions? Here you go! 

5. Explain how memory management is handled in iOS. 


As iOS applications have memory and other hardware and system constraints, memory management is important. 

Swift and Objective-C use Automatic Reference Counting (ARC). ARC tracks strong references to instances of classes. It increases or decreases their reference count accordingly when you assign or unassign instances of classes to constants, variables, and properties. ARC deallocates memory used by  objects when the reference count is dropped to zero. It doesn’t increase or decrease the reference count of value types because these are copied when they’re assigned. If not specified otherwise, all references are strong. 

6. Explain the advantages of the Realm framework.


The Realm framework only needs a small amount of code and it’s available in Swift and Objective-C. SQLite and Core Data have slower performance in the framework and database files can be shared easily between iOS and Android devices. Realm is free and there is no limit to the data that can be stored, while it’s consistent and offers consistent speed. 

7. What are an app ID and a bundle ID and why are they used? 


An app ID is a two-part string that’s used to identify one or more apps from a single development team. This string consists of a Team ID and a bundle ID search string with a period separating the two parts. The Team ID is supplied by Apple and it’s unique to a specific development team. 

The bundle ID search string is supplied by the developer and is used to match the bundle ID of a single app or a set of bundle IDs for a group of apps. The bundle ID designs every application. It’s specified in Xcode, which can have many targets and output many apps. For instance, an app that has a free and a pro version is a typical use case. 

Over to you!

There you have it! Now you know what the top iOS developer interview questions are. 

Use these interviews to run smooth and effective interviews that help you identify the right developers.

But after your interviews, you’re not done yet. You also need to assess their technical skills.

That’s what CodeSubmit helps you with. CodeSubmit is a technical skill assessment and live coding interview SaaS. 

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