IOS Interview Questions

1. What are the important characteristics of IOS?

Ans: Below are a few important characteristics of IOS:

• The display is paramount regardless of its size
• Device orientation can change
• Apps respond to gestures, not clicks
• People interact with one app at a time
• Onscreen users help is minimal 
• Safari’s on IOS provides the web interface.

2. Mention the differences between IOS and Android devices?

Ans: 

3. Mention the differences between IOS and Windows devices?

Ans: The below table will explain the major differences between IOS and Windows

4. Which JSON framework is supported by IOS (iPhone OS)?

Ans:

• SBJSON framework is mainly supported by IOS devices. This framework is available in the form of a JSON parser and generator for object-oriented programming language. JSON framework is a superset of the programming language called C and offers object-oriented features and capabilities.
• SBJSON APIs is a flexible application programming interface and offers additional controlling features to handle JSON easier way.

5. Name the framework that is used to construct the application user interfaces for IOS?

Ans: 

UIkit framework: this type of framework is mainly used to develop user interfaces. The following are the few features of using the UIKIT framework;

• Event handling
• Drawing model
• Windows
• Views
• Controls.

UIkit. The framework offers the complex infrastructures required to construct and manage IOS application devices.

• UIkit’s windows and view architecture used to manage user interfaces
• Event handling infrastructures needed to respond to the user inputs.

6. How can you respond to state transitions on your app?

Ans: There are 4 methods used to respond to state transitions such as;

• ApplicationDidBecomeActive () method: this method is used to run the foregroup apps
• ApplicationDidEnterBackground () method: this method is used to execute the codes
• ApplicationWillEnterForeground () method: this method is used to execute the codes which are running background
• ApplicationWillTerminate () method: this method is called to terminate the apps.

7. What are the features added in IOS 9?

8. What is the difference between RETAIN and ASSIGN?

Ans: ASSIGN is used to create references from one object to another, the below program will explain this;

If (_variable ! = object)

{

  [_variable release];

  _variable = nil;

  _variable = object;

}

RETAIN used to create the differences between one object and another;

If (_variable! = object)

{

  [_variable release];

  Variable = nil;

  _variable = [object retain];
 
}

9. Which are the ways of achieving concurrency in IOS?

Ans: Below are the three ways to achieve concurrency;

• Threads
• Dispatch queues
• Operation queues.

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10. Explain the different types of IOS application states?

Ans: The different application states of IOS included are;

Not running state: this state is used when the app has not been launched yet, or that was terminated by the system.

Inactive: this state is used when the application is running in the foreground and not receiving any events.

Active state: when applications are running in the foreground and receiving events by that time this state is used.

Background state: this state is used to run the application in the background and execute the codes.

Suspended state: this state is used to terminate the program.

11. Which is the application thread from where UIKIT classes should be used?

Ans: A UIKIT class uses the application thread from the application’s main thread.

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

13. What are layer objects in IOS?

Ans: The layer objects are nothing but data objects which represent the visual features, views and render the contents. These layers are custom layers that are added to the interfaces to execute any complex animations.

14. What is Sprite kit and Scene kit?

15. What is SWIFT?

Ans: A SWIFT is one of the programming languages used in the development of IOS applications. SWIFT language adopts safe programming patterns and offers many modern features to make programming easier to implement, flexible, and more fun to write.

16. What is meant by ARC?

Ans. ARC, or Automatic Reference Counting, is a compiler-level feature used by Swift to track and manage an application's memory usage. It helps release the memory of class instances when there is no need for memory reserved. It does so by initializing and deinitializing system resources. In iOS development, the role of ARC concepts is highly crucial.

17.Define iBeacons.

Ans. iBeacons is newly introduced by Apple, a Bluetooth wireless technology. It's a new technology useful for iPhone and iOS users to get location-based information and services. These small-scale wireless transmitters use Bluetooth low-energy technology to transmit data or signals to nearby smart devices.

18. Explain what GCD is in iOS?

Ans. In iOS, GCD refers to Grand Central Dispatch, a low-level API that helps you manage different concurrent operations. It can also help you enhance your app's responsiveness by delaying computationally rigorous tasks to the context.

19. What is meant by Operator Overloading?

Ans. In iOS, operator overloading refers to adding new operators by altering existing operators to perform different activities. It allows us to alter the way of working of existing operators using some specific structures. The various operators includes +, *, /, etc. symbols.

20. Explain KVO in iOS.

Ans. KVO stands for Key-Value Observing, a technique for observing changes to the property value. If we have an object including some cited variables, then KVO enables other objects to monitor the modifications to any of these variables.

21. What do you mean by Dynamic Dispatch?

Ans. In iOS, the term Dynamic Dispatch means that a program decides at run time which implementation of a specific function it needs to invoke. It is useful when we need to call on our methods similar to the object method.

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22. Explain Cocoa and Cocoa Touch in iOS.

Ans. Cocoa is an app development environment useful for OS X and iOS. Also, it helps in creating software codes to run on iOS and includes the Foundation and Appkit frameworks. Further, we can use it for referring to any class or object based on the Objective-C runtime.

Cocoa Touch is an app development environment for iOS written in Objective-C language. It also consists of Foundation and UIKit frameworks. Cocoa Touch is useful in developing software apps for the products like iPhones, iPad, etc.

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23. What do you understand from TVMLkit?

Ans. The term TVML refers to Apple TV Markup Language. TVMLkit acts as a link between JavaScript, TVML, and tvOS apps. We can use a JavaScript environment to build TVML objects, styles, and views. Moreover, the TVMLkit framework allows you to include JavaScript and TVML files into your binary apps. Also, it helps to build various client-server apps.

24. Define Bundle ID.

Ans. The bundle ID is defined in each app which is useful for both OS X and iOS. A bundle identifier can easily identify your apps' updates. Moreover, Bundle ID is mentioned in XCode. A single XCode project can include many targets and output different apps.

25. List out the most important data types found in Objective-C.

Ans. The following are the most important data types found in Objective-C.

• Bool
• NSString
• NSUInteger
• NSInteger

26. Name the different programming languages used in iOS Development.

Ans. The following coding languages are used in iOS development.

• JavaScript
• HTML 5 
• .Net
• Swit
• Objective-C

27. Define Synchronous and Asynchronous Tasks.

Ans. Synchronous refers to the tasks that will execute in order. In this type of operation, the thread must wait for the completion of the activity before proceeding further. 

Asynchronous is the opposite of synchronous or "out of order ."In this call, the tasks may or may not be executed in order. These tasks allow a user to process different requests at the same time. It helps to complete more tasks within a short time.

28. Define NSError in Swift.

Ans. In Swift, the NSError class is a Cocoa class. The NSError object holds the information about an error condition in an extendable and object-oriented way. Moreover, it consists of attributes like a predefined error domain, a domain-specific error code, and a user details dictionary that includes app-specific information.

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29. What do you mean by Enum or Enumerations?

Ans. It is a user-defined data type or a class type defined by the keyword "Enum ."Further, it includes a certain set of values that allows a user to work with those values in a type-safe or intact way within the code.

30. Define Guard Statement and its benefits.

Ans. A guard statement is used when one or more requirements are not met. Further, passing a program control out of a domain or realm is useful.

The following are the various benefits of a Guard Statement

• It offers an early exit from the function.
• It provides a way to unwrap optionals safely.
• Also, it doesn't include nested if let statements.

31. Explain Atomic and NonAtomic properties in iOS.

Ans. Atomic properties have default behavior and are not much faster, and they guarantee always to return a completely initialized object. Also, the Atomic properties come at the expense of performance. 

On the other hand, nonatomic properties don't have default behavior and are much faster. But they cannot deal with many incoming requests at the same time.

32. What are the benefits of using Swift language?

Ans. The following are the important benefits of Swift language.

• It's easy to read and maintain.
• Swift is highly fast and includes dynamic libraries.
• It's a very safe and secure programming language.
• Also, it has concise code and effectively helps in managing memory.

33. Define Tuple in Swift.

Ans. It's a temporary container for various values which holds a list of comma-separated types, and the same is bounded in parentheses. You can use it as a function's return type to allow the function to return a single tuple that holds different values.

34. What is the use of KVC?

Ans. KVC or Key-Value Coding is useful for accessing a value using a string. In other words, it means indirectly accessing an object's properties using strings to locate properties.

35. Define Responder chain iOS.

Ans. In iOS, the Responder chain is a hierarchy of objects that have the chance of responding to the events received. It is a series of events that occurs once the user interacts with the iPhone's application.