Top iOS Interview Questions You Must Prepare In 2020

The Verge reports that, as of January 2018, there are multi-billion active Apple devices in the world. With the number of iOS users growing steadily across the world, the future looks bright for iOS app developers. Apple and iOS devices continue to have a loyal customer base, helped in part by innovative new devices such as Apple TV and Apple Watch. With that said, an iOS app development certification is probably the easiest way to hone and prove your skills in the same. There has never been a better time to become an iOS developer. If you are preparing to break into a career in iOS app development, look no further! We have created a list of top frequently-asked iOS interview questions that will help you ace your iOS job interview.

However, if you have already given an iOS interview, or have more questions, we encourage you to add them in the comments tab below. Our experts will answer them for you.To more info:ios online course

iOS Interview Questions

1. What is Cocoa and Cocoa Touch?

Cocoa vs Cocoa Touch

Cocoa	Cocoa Touch
1. Application development environments for OS X	1. Application development environments for iOS
2. Includes the Foundation and AppKit frameworks	2. Includes Foundation and UIKit frameworks
3. Used to refer any class/object which is based on the Objective-C runtime & inherits from the root class	3. Used to refer the application development using any programmatic interface

2. Which JSON framework is supported by iOS?

• iOS supports SBJson framework.
• SBJson is a JSON parser and generator for Objective-C.
• It provides flexible APIs and additional control, making JSON handling easier.

3. What is the difference between atomic and nonatomic properties? Which is the default for synthesized properties?

Properties specified as atomic always return a fully initialized object. This also happens to be the default state for synthesized properties. But, if you have a property for which you know that retrieving an uninitialized value is not a risk (e.g. if all access to the property is already synchronized via other means), then setting it to nonatomic can give you better performance than atomic.

4. Differentiate ‘app ID’ from ‘bundle ID’. Explain why they are used.

An APP ID  is a two-part string used to identify one or more apps from a single development team. The 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 is unique to a specific development team, while the bundle ID search string is supplied by the developer to match either the bundle ID of a single app or a set of bundle IDs for a group of apps.

The bundle ID defines each App and is specified in Xcode. A single Xcode project can have multiple targets and therefore output multiple apps. A common use case is an app that has both lite/free and pro/full versions or is branded multiple ways.

5. Which are the ways of achieving concurrency in iOS?

The three ways to achieve concurrency in iOS are:

• Threads
• Dispatch queues
• Operation queues

6. Explain the different types of iOS Application States.

The different iOS application states are:

• Not running state: when the app has not been launched or was running but was terminated by the system.
• Inactive state: when the app is running in the foreground but is currently not receiving events. An app stays in this state briefly as it transitions to a different state. The only time it stays inactive is when the user locks the screen or the system prompts the user to respond to some event such as a phone call or SMS message.
• Active state: when the app is running in the foreground and is receiving events. This is the normal mode for foreground apps.
• Background state: when the app is in the background and executing code. Most apps enter this state briefly on their way to being suspended. However, an app that requests extra execution time can remain in this state for some time. Also, an app being launched directly into the background enters this state instead of the inactive state.
• Suspended state: A suspended app remains in memory but does not execute any code. When a low-memory condition occurs, the system may purge suspended apps without notice to make more space for the foreground app.

7. Which is the framework that is used to construct application’s user interface for iOS?

The UIKit framework is used to develop application’s user interface for iOS. It provides event handling, drawing model, windows, views, and controls specifically designed for a touch screen interface.

8. Which is the application thread from where UIKit classes should be used? 

UIKit classes should be used only from an application’s main thread.

9. Which API would you use to write test scripts to exercise the application’s UI elements?

UI Automation API is used to automate test procedures. JavaScript test scripts that are written to the UI Automation API simulate user interaction with the application and return log information to the host computer,more info visit:android development course

10. When would you say that an app is not in a running state?

An app is said to be in ‘not running’ state in the following cases:
– When it is not launched.
– When it gets terminated by the system during running.

11. When is an app said to be in active state? 

An app is said to be in active state when it is running in the foreground and is receiving events.

12. Which are the app’s state transitions when it is launched?

An app is said to be in not running state before its launch.

After briefly transitioning through the inactive state, it moves to the active or background state when it is launched.

13. Which is the state an app reaches briefly on its way to being suspended?

An app enters background state briefly on its way to being suspended.

14. What is Swift and what is Objective-C?

Objective-C is the primary programming language you use to write software for OS X and iOS. It’s a superset of the C programming language and provides object-oriented capabilities and a dynamic runtime. Objective-C inherits the syntax, primitive types, and flow control statements of C and adds syntax for defining classes and methods. It also adds language-level support for object graph management and object literals while providing dynamic typing and binding, deferring many responsibilities until runtime.

Swift is a new programming language for iOS, OS X, watchOS, and tvOS apps that builds on the best of C and Objective-C, without the constraints of C compatibility. Swift adopts safe programming patterns and adds modern features to make programming easier, more flexible, and more fun. Swift feels familiar to Objective-C developers and is friendly to new programmers.

Source: Apple developer library

15. What is SpriteKit and what is SceneKit?

SpriteKit is a framework for easy development of animated 2D objects.

SceneKit is a framework inherited from OS X that assists with 3D graphics rendering.

SpriteKit, SceneKit, and Metal are expected to power a new generation of mobile games that redefine what iOS devices’ powerful GPUs can offer.

16. What are iBeacons?

iBeacon.com defines iBeacon as Apple’s technology standard which allows Mobile Apps to listen for signals from beacons in the physical world and react accordingly. iBeacon technology allows Mobile Apps to understand their position on a micro-local scale, and deliver hyper-contextual content to users based on location. The underlying communication technology is Bluetooth Low Energy.

17. What is autorealease pool?

Every time -autorelease is sent to an object, it is added to the inner-most autorelease pool. When the pool is drained, it simply sends -release to all the objects in the pool.

Autorelease pools are a convenience that allows you to defer sending -release until “later”. That “later” can happen in several places, but the most common in Cocoa GUI apps is at the end of the current run loop cycle.

18. Differentiate between ‘assign’ and ‘retain’ keyword.

Retain -specifies that retain should be invoked on the object upon assignment. It takes ownership of an object.

Assign – specifies that the setter uses simple assignment. It is used on attribute of scalar type like float,int.

19. What are layer objects?

Layer objects are data objects which represent visual content and are used by views to render their content. Custom layer objects can also be added to the interface to implement complex animations and other types of sophisticated visual effects.

20. Outline the class hierarchy for a UIButton until NSObject.

UIButton inherits from UIControl, UIControl inherits from UIView, UIView inherits from UIResponder, UIResponder inherits from the root class NSObject.more info visit:

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