Top 25 iOS Interview Questions and Answers in 2024

Editorial Team

iOS Interview Questions and Answers

We have developed a list of the top 25 iOS interview questions to assist you in preparing for your upcoming iOS job interview. In addition, this article contains numerous questions of varying levels of difficulty and sample answers to aid you with revision.

1. In Your Own Words, What Is A Memory Leak?

Memory leaks occur when programmers forget to erase heap memory after creating it. By decreasing the quantity of available memory, memory leaks diminish the computer’s performance. Eventually, in the worst-case scenario, too much of the available memory may be allocated, causing the system or device to stop functioning properly, the program to fail, or the system to significantly slow down. For example, a memory leak can occur in object-oriented programming when an object is saved in memory but cannot be accessible by the running function.

2. What Kinds Of Tests Can You Create To Evaluate Your iOS Application, And Why Are Testing Useful?

There are two primary categories of iOS automated tests:

  • First, unit tests ensure that the source code produces the desired outcomes. For instance, verifying that a function returns the desired outcome when supplied with a particular parameter.
  • User interface (UI) tests to ensure a user interface behaves as expected. A UI test might, for instance, programmatically press on a button that should transition to a new screen before checking to see if the anticipated screen loaded and included the anticipated content.

Testing enables faults in the application to be corrected. Automated tests can increase testing efficiency, save time, and reduce development expenses.

3. Kindly Explain Code Signing For iOS Apps.

Signing an application enables the system to determine who signed the application and validate that it has not been altered. Signing is required to submit to the App Store. OS X and iOS validate the signatures of applications downloaded from the App Store to prevent executing applications with incorrect signatures. It allows users to trust that the application was signed by an Apple-authorized source and has not been altered.

Xcode uses your digital identity to sign your application during the build phase. This digital identity is comprised of a pair of public and private keys as well as a certificate. First, cryptographic functions use the private key to generate the signature. Next, apple issues the certificate, which contains your public key and identifies you as the key pair’s owner.

4. What Exactly Is A Responder Chain?

When an event, such as touch, occurs in a view, it sends the event to a chain of UIResponder objects connected with the UIView. The initial UIResponder is the UIView itself; if it does not handle the event, the chain continues until a UIResponder does. The chain will consist of UIViewControllers, parent UIViews, and their respective UIViewControllers; if none handle the event, the UIWindow is questioned to see whether it can handle it, and if that fails, the UIApplicationDelegate is questioned.

5. How Does Nsnotificationcenter Function?

Apple has provided NSNotificationCenter as an Observer Pattern in the Cocoa library. A listener registers with a broadcaster via a predetermined protocol. Later, the broadcaster is instructed to tell all of its listeners, at which point it performs a function on each listener and passes along specified arguments. It enables the asynchronous transmission of messages between two distinct objects that need only be aware of the broadcaster and not each other.

6. What Is GCD, And How Does It Work?

GCD is the most used API for managing concurrent code and executing actions at the Unix system level asynchronously. GCD provides and manages task queues. When an application retrieves data from an API, for instance, the network request should occur in a background thread, while the display of the data in the view and any UI adjustments should occur in the main thread.

7. What Are The iOS Delegate Methods?

Delegate methods are a simple and influential pattern in which one object in a program works for or with another. The delegating object maintains a reference to the delegated object and sends it a message at the appropriate moment.

The delegate may reply to the message by modifying the appearance or status of itself or other application objects. In some situations, it may return a value that alters how an imminent event is handled. Delegation’s primary benefit is the ability to alter the behavior of multiple objects within a single object.

8. What Does The Term “App Thinning” Mean?

The app store and operating system optimize the installation of iOS, tvOS, and watchOS applications by adapting app delivery to the capabilities of the user’s specific device with a low footprint. This optimization, known as app thinning, enables the creation of apps that utilize the greatest number of device features, consume the smallest amount of disk space, and are compatible with future Apple updates. Through app thinning, iOS 9 enables mobile app developers to reduce the size of their software on customers’ mobile devices. Utilizing one or a mixture of three techniques known as Slicing, On-Demand Resources, and BitCode is required.

9. What’s The Distinction Between Synchronous And Asynchronous Tasks?

Similarly, synchronous can be defined as in order. When a synchronous operation is performed, all subsequent actions must wait for its completion before continuing. In contrast, “asynchronous” can also mean “out of sequence.” When you accomplish something asynchronously, you can execute the following code immediately, and the asynchronous operation will eventually occur. It is likely to execute on a thread distinct from the rest of the code. It could be rescheduled on the same thread later, and you could be notified when it is completed.

10. What Is The Definition Of A Completion Handler?

Swift completion handlers are functions that are called when a job completes. Hence, it is also known as a callback function. Another function receives as an input a callback function. When this function finishes doing a task, the callback function is executed. Completion handlers are a wonderful solution if an app makes an API request; we need to do something spectacular, such as modifying the UI to display the data from the API call after the operation. Apple’s APIs, such as dataTaskWithdemand, will have completion handlers; adding these to your code can make it more aesthetically beautiful and functional.

11. What Are The Various States That An iOS Application Can Be In?

  • Background: Most apps go here before getting suspended. If an app wants more time to run, it will do so. Also, apps are launched right into the background instead of inactive.
  • Suspended: In suspended mode, no code is executed. When memory is low, the system automatically deletes suspended apps to create room for the main app.
  • Active: Active State is iOS’ principal executive state. In forefront mode, the UI is available.
  • Not running: The app is in the Not operating state if it hasn’t been launched or isn’t visible on the screen, or if the user or OS terminated it.
  • Inactive: In this state, the software runs in the background without getting events.

12. How Is iOS’s Memory Management Handled?

Memory management is essential for all programs, but it is especially necessary for iOS applications due to memory and other constraints. Swift uses a more intelligent method for managing memory: Automatic Reference Counting (ARC). It automatically releases the memory occupied by class instances when they are no longer required. Nevertheless, ARC only applies to class instances. Because Structure and Enumerations are Value types in Swift, their instances are not counted. Due to inadequate memory management, memory leaks and system crashes are too typical in iOS applications.

13. What Is An Optional, And What Issue Do They Address?

Swift options are a potent source of safety, but they can be bothersome if scattered throughout your code. Swift’s nil coalescing operator aids in resolving this issue by either unwrapping an optional if it has a value or providing a default if the optional is undefined. In addition, properties, methods, and subscripts may return an optional, which returns a value if the variable exists or nil otherwise—chaining many requests together is known as Optional chaining. It is an alternative to Force Unwrapping, which will be described in further depth below.

14. What Is The Distinction Between Strong And Weak?

Strong indicates that the reference count will increase, and the reference will be maintained for the object’s lifetime. Conversely, Weak indicates that we are pointing to an item without increasing its reference count. It is frequently employed when establishing a parent-child bond. It is because the parent has a strong relationship with the child, whereas the child has a weak relationship with the parent. Common examples of weak references include delegate properties and subviews/controls of the main view of a view controller, as those views are already strongly owned by the main view.

15. In Objective-C Programming Language, What Is The Difference Between A Category And An Extension?

A category and an extension are functionally equivalent in that they can add instance and class methods to a class. However, this is only possible if the class being extended’s source code is available at compile time. Therefore, we cannot extend classes like NSString. Instead, an NSString category would be utilized to provide new methods.

16. What Is The Difference Between Delegating And Notifying?

Both methods are employed to transmit values and messages to interested parties. Apple promotes the delegate pattern, which is used for one-on-one communication. In delegation, class-raising events will often provide a property for the delegate and demand it implement a protocol. The delegating class can then invoke the protocol methods of the delegated class. Notification enables a class to communicate events to all interested parties within an application. The broadcasting class does not need to know anything about the event’s listeners; hence, notification is highly effective for decoupling application components.

17. What’s The Distinction Between Copying And Retaining?

Retaining an object increases its retain count by one in most situations. It will aid in remembering the object and prevent it from getting blown away. If you have a retained copy, you must share it with the person who handed it to you. Copying an item should always result in a new object with identical values.

18. What Methods Exist For Achieving Concurrency On iOS?

  • Threads: A thread is a sequence of instructions that runtime can execute. Each process contains a minimum of one thread. Commonly referred to as the main thread, the main thread on which an iOS process is initiated is known as the main thread. It is the thread that creates and manages all UI elements.
  • Dispatch queues are FIFO queues to which an application may submit object-based block tasks.
  • Operation queue: A queue for operations invokes Operation objects based on their priority and readiness. Once an operation has been added to a queue, it remains there until it has completed its task. You cannot delete an operation from a queue straight after adding it.

19. What Is The Distinction Between Viewdidload And Viewdidappear?

 ViewDidLoad is invoked when the view is loaded, regardless if it was produced from a Xib file, a storyboard, or programmatically in loadView. ViewDidAppear is invoked whenever the view is displayed on the device. The choice relies on the data’s intended usage. For example, if the data is relatively static and unlikely to change, it can be loaded and cached in viewDidLoad. However, if the data changes often, viewDidAppear is superior for loading it. In all cases, the data should be loaded asynchronously on a background thread to prevent blocking the user interface.

20. What Are The Numerous iOS App Distribution Methods?

Depending on the developer program you are a part of, Apple offers three distribution options for applications:

  • App Store against iTunes: Distribute an application through the iTunes Store.
  • In-House: Publish an application for firm personnel in-house. This option replaces the App Store option for Apple Developer Enterprise program members.
  • Using the Apple Developer Program for Ad-Hoc Deployment: Apple allows developers to use the Ad-hoc app deployment option for private beta testing or interim release. In this case, the developer will send each user the program binary via a download URL or email.

21. Why Is Xcode Needed In iOS App Development?

Apple’s only supported method for app development is Xcode. Therefore, if a developer wishes to create iOS or macOS applications, they must utilize it. Some third-party solutions do not require a developer to utilize Xcode; however, Apple does not support them, and they frequently experience problems. Xcode includes excellent debugging tools that enable developers to quickly resolve app issues. It also includes project management tools that enable the orderly management of graphic assets and code files.

22. What Are The Different Types Of iOS Notifications?

Local notifications and remote notifications are methods for informing users when new data becomes available for an application, even if the application is not currently running in the foreground. The following describes the distinction between local and distant notifications:

  • With local notifications, the app configures the notification data locally and gives them to the system, which then handles the notification delivery while the app is not in the forefront. Local notification support is available on iOS, tvOS, and watchOS.
  • Via remote notifications, one of the organization’s servers pushes data to user devices using the Apple Push Notification service. Notifications received remotely are supported on iOS, tvOS, watchOS, and macOS.

23. What Is The Difference Between Swift’s Functions And Methods?

Functions are autonomous sections of code that execute a specified task. A function is given a name used to “call” the function to do its work when required. With functions, there is no concept of the self.

Methods are functions that correspond to a specific type. For example, classes, structures, and enumerations can all include instance methods, encapsulating specialized responsibilities and capabilities for manipulating instances of a certain type. 

24. When Might Core Data Be Preferred To Nsuserdefault?

 NSUserDefaults should only be used to store preferences and app settings. You should not store sensitive information or user data in them. UserDefaults can be used in tiny applications or to hold flags. However, do not utilize UserDefaults to store large amounts of data, including image caching.

CoreData is a fully-fledged framework for persistent data that enables huge data transactions. CoreData enables the development of a relational entity–attribute model for storing user data. Utilize CoreData for large projects. CoreData entities are superior to arbitrary values saved via keys, even if they are serialized to objects afterward.

25. What Are The Numerous Options For iOS Data Storage?

  • NSUserDefaults – intended for storing little pieces of information like settings, preferences, and specific values.
  • Property list – Property lists are an additional effective method for storing our info. However, similar to user defaults, it is not designed to store significant amounts of information.
  • SQLite is a small embedded relational database.
  • Keychains store highly sensitive and secure information, such as passwords and secret codes.
  • Saving Files – Save all file kinds directly to the file system.

Core Data – Apple’s persistence technology – enables programs to persist and retrieve data in any form. Core Data is not strictly a database, but it keeps its data in databases (an SQLite database, to be precise).


As An Ios Developer, You Should Stay Abreast Of Ios Community Developments. Follow Apple developer-related News, Read Blogs, Listen To Podcasts, And Be Eager To Get New Knowledge. Explore, Practice, And Do Not Forget To Review Our Collection Of Leading Ios Interview Questions Before Your Next Interview.