iOS Interview Questions and Answers

It’s time to land your dream job. If you are planning to build a career as an iOS Developer, prepare in advance with these frequently asked iOS interview questions. These iOS Developer interview questions have been answered by the top industry experts and have been proven to be helpful. Interview questions for ios Developer here will boost your knowledge and confidence in a short period of time. With these basic ios interview questions, you will be able to answers questions like What happens when the app receives a push notification?’, ‘Ways to Modify below code using Dependency Injection’, ‘What is the difference between the consumable and non-consumable type of in-app purchase?’. Be prepared and chase your dream job.

1.What is SceneKit?

Ans:

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

2.Which JSON framework is supported by iOS?

Ans:

• iOS supports the 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?

Ans:

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.

Ans:

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?

Ans:

The three ways to achieve concurrency in iOS are:

• Threads
• Dispatch queues
• Operation queues

6.Explain the different types of iOS Application States.

Ans:

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 an application’s user interface for iOS?

Ans:

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?

Ans:

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?

Ans:

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.

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

Ans:

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 an active state? 

Ans:

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?

Ans:

An app is said to be in no 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?

Ans:

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

14.What is Swift ?

Ans:

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.

15.What is SpriteKit?

Ans:

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

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?

Ans:

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 an autorelease pool?

Ans:

Every time -autorelease is sent to an object, it is added to the innermost 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’ keywords.

Ans:

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 attributes of scalar type like float,int.

19.What Is The Use Of “Dynamic” Keywords?

Ans:

Instructs the compiler not to generate a warning if it cannot find implementations of accessor methods associated with the properties whose names follow.

20.Define App Bundle?

Ans:

When you build your iOS app, Xcode packages it as a bundle. A bundle is a directory in the file system that groups related resources together in one place. An iOS app bundle contains the app executable file and supporting resource files such as app icons, image files, and localized content.

21.Name The Application Thread From Where Uikit Classes Should Be Used?

Ans:

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

22.What Is The Main Difference Between Nsarray And Nsmutablearray ?

Ans:

NSArrayʼs contents can not be modified once itʼs been created whereas a NSMutable Array can be modified as needed, i.e items can be added/removed from it.

23.Explain Retain Counts?

Ans:

Retain counts are the way in which memory is managed in Objective-C. When you create an object, it has a retain count of 1. When you send an object a retain message, its retain count is incremented by 1. When you send an object a release message, its retain count is decremented by 1. When you send an object an auto release message, its retain count is decremented by 1 at some stage in the future. If an objectʼs retain count is reduced to 0, it is deallocated.

24.What Is The Main Difference Between Frame And Bounds?

Ans:

The frame of a view is the rectangle, expressed as a location (x,y) and size (width,height) relative to the super view it is contained within. The bounds of a view is the rectangle, expressed as a location (x,y) and size (width,height) relative to its own coordinate system (0,0).

25.What Is Outline The Class Hierarchy For A Uibutton Until Nsobject ?

Ans:

• UIButton inherits from UIControl
• UIControl inherits from UIView
• UIView inherits from UIResponder
• UIResponder inherits from the root class NSObject.

26.Is it possible to inherit the structures?

Ans:

No, you cannot inherit the structures.

27.Define Code Signing?

Ans:

Signing an application allows the system to identify who signed the application and to verify that the application has not been modified since it was signed. Signing is a requirement for submitting to the App Store (both for iOS and Mac apps). OS X and iOS verify the signature of applications downloaded from the App Store to ensure that they do not run applications with invalid signatures. This lets users trust that the application was signed by an Apple source and has n’t been modified since it was signed.

28.What Is an Iphone?

Ans:

iPhone is a combination of internet and multimedia enabled smartphone developed by Apple Inc. iPhone functions as a camera phone, including text messaging, and visual voicemail. The iPhone is a portable media player that resembles a video iPod. It has a user interface that is built around the multi-touch screen including a virtual keyboard.

29.What Is An Iphone App?

Ans:

An iPhone app is a program that runs on our iPhone/iPod Touch. It enables us to accomplish a certain task. They could be utility apps, games, enterprise apps, entertainment apps, apps to access our bank account etc

30.What Is The Introduction To Iphone Application Development?

Ans:

In 2007, Apple entered the cellular phone business with the introduction of the iPhone, a multi-touch display cell phone, which also includes the features of iPod.

31.Multitasking Support Is Available From Which Version?

Ans:

The iOS 4.0 version supports multitasking.

32.Explain The Difference Between Nsoperationqueue Concurrent And Nonconcurrent?

Ans:

In the context of an NSOperation object, which runs in an NSOperationQueue, the terms concurrent and non-concurrent do not necessarily refer to the side-by-side execution of threads. Instead, a non-concurrent operation is one that executes using the environment that is provided for it while a concurrent operation is responsible for setting up its own execution environment.

33.What Are The Features Of Iphone 3gs?

Ans:

Video: Videos can be edited, shared. High quality VGA video can be shot in portrait or landscape.
3 Megapixel Camera: Still photos with greater quality can be taken.
Voice control: It recognizes the names in contacts and recognizes the music on iPod.
Compass: iPhone 3GS has built-in digital compass, used to point the way.
Internet Tethering: Internet surfing can be done from anywhere. A 3G connection can be shared on iphone3 with Mac notebook or laptop.

34.Why Are Iphone Apps Popular?

Ans:

Give our business a whole new way of transacting business for millions of users. iPhones are the market leaders in the smartphone segment. The iPhone has become a great device to surf the internet, play games, interact with social networks and transact business.

35.Where Can You Test Apple Iphone Apps If You Don’t Have The Device?

Ans:

iOS Simulator can be used to test mobile applications. The Xcode tool that comes along with iOS SDK includes Xcode IDE as well as the iOS Simulator. Xcode also includes all required tools and frameworks for building iOS apps.  However, it is strongly recommended to test the app on the real device before publishing it.

36.Does Ios Support Multitasking?

Ans:

iOS 4 and above supports multitasking and allows apps to remain in the background until they are launched again or until they are terminated.

37.What Is The Nscoder Class Used For?

Ans:

NSCoder is an abstract Class which represents a stream of data. They are used in Archiving and Unarchiving objects. NS Coder objects are usually used in a method that is being implemented so that the class conforms to the protocol. (which has something like encode Object and decode Object methods in them).

38.What Is an Iphone Os?

Ans:

• iPhone OS runs on iPhone and iPod touch devices.
• Hardware devices are managed by iPhone OS and provide the technologies needed for implementing native applications on the phone.
• The OS ships with several system applications such as Mail, Safari, Phone, which provide standard services to the user.

39.What Is The Difference Between Shallow Copy And Deep Copy?

Ans:

Shallow copy is also known as address copy. In this process you only copy address not actual data while in deep copy you copy data.

40.What Are The Requirements For Developing Iphone Apps?

Ans:

Mac OS 10.5/10.6 iPhone SDK (Software Development Kit 3.0/4.0).
IPhone SDK consists of:
a. IDE to develop iPhone Apps is XCode(This tool is inbuilt in iPhone SDK)
b. Interface Builder This is used to design GUI of Apps(Inbuilt feature of iPhone SDK)
c. Instruments  This is used to check any memory leaks in our apps (Inbuilt in SDK)
d. Simulator This is used to test our apps before deploying into a real device.

41.What Are The Popular Apps For Iphones?

Ans:

iphone apps are
a. Facebook-Social networking
b. Doodle Buddy-drawing
c. Pandora Radio-radio on our iPhone
d. Help-restaurant reviews

42.What Is an Iphone Reference Library?

Ans:

iPhone reference library is a set of reference documents for iPhone OS. It can be downloaded by subscribing to the iPhone IOS Library doc set. Select Help>Documentation from X code, and click the subscribe button next to the iPhone IOS Library doc set, which appears in the left column.

43.What Is an Iphone Sdk?

Ans:

iPhone SDK is available with tools and interfaces needed for developing, installing and running custom native applications. Native applications are built using the iPhone OS’s system frameworks and Objective-C language and run directly on iPhone OS. Native applications are installed physically on a device and can run in presence or absence of network connection.

44.What Is Iphone Architecture?

Ans:

iPhone architecture is similar to Mac OS X architecture
It acts as an intermediary between the iPhone and iPod hardware and the applications appearing on the screen.
The user created applications never interact directly with the appropriate drivers, which protects the user applications from changes to the hardware.

45.What Are The Location Services?

Ans:

Applications such as Maps, camera and compass are allowed to use the information from cellular, WiFi and Global Positioning System networks for determining the approximate locations.
The location is displayed on the screen, using a blue marker.

46.Describe The Functionality Of The Accelerometer Of An Iphone?

Ans:

the iPhone responds to motion using a built-in accelerometer. The accelerometer detects the movement and changes the display accordingly, at the time of rotating the iPhone from portrait to landscape.

47.what is Cocoa and Cocoa Touch?

Ans:

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

48.What are layer objects?

Ans:

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.

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

Ans:

UIButton inherits from UIControl, UIControl inherits from UIView, UIView inherits from UIResponder, UIResponder inherits from the root class NSObject.

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

Ans:

State transitions can be responded to state changes in an appropriate way by calling corresponding methods on the app’s delegate object.

For example:

• applicationDidBecomeActive( ) method: To prepare to run as the foreground app
• applicationDidEnterBackground( ) method: To execute some code when the app is running in the background that may be suspended at any time
• applicationWillEnterForeground( ) method: To execute some code when the app is moving out of the background
• applicationWillTerminate( ) method: Called when the app is being terminated

51.What are the features added in iOS 9?

Ans:

The following features are added in iOS 9:

• Intelligent search: It is an excellent mechanism to learn user habits and act on that information—open apps before we need them, make recommendations on places we might like, and guide us through our daily lives to make sure we’re where we need to be at the right time.
• Siri: It is a personal assistant to the users that is able to create contextual reminders and search through photos and videos in new ways. Swiping right from the home screen brings up a new screen that houses ‘Siri Suggestions,’ putting favorite contacts and apps right on our fingertips, along with nearby restaurant and location information and important news.
• Deeper search capabilities: It can show results such as sports scores, videos, and content from third-party apps, and we can even do simple conversions and calculations using the search tools on our iPhone or iPad.
• Performance improvements: The following built-in apps have been improved:
• • Notes including new checklists and sketching features
  • Maps now offering transit directions
  • Mail allowing for file attachments
  • New ‘News’ app that learns our interests and delivers relevant content we might like to read
  • Apple Pay being improved with the addition of store credit cards and loyalty cards
  • ‘Passbook’ being renamed to ‘Wallet’ in iOS 9
• San Francisco font
• Wireless CarPlay support
• Optional iCloud Drive app: It is a built-in two-factor authentication system with optional longer passwords for better security.

52.What are the different ways to specify the layout of elements in UIView?

Ans:

Here are a few common ways to specify the layout of elements in UIView:

• Using InterfaceBuilder, we can add an XIB file to our project, layout elements within it, and then load XIB in our application code (either automatically, based on naming conventions, or manually). Also, using InterfaceBuilder, we can create a storyboard for our application.
• We can write our own code to use NSLayoutConstraints and have elements in a view arranged by Auto Layout.
• We can create CGRects describing the exact coordinates for each element and pass them to UIView’s (id)initWithFrame:(CGRect)frame method.

53.Describe managed object context and its function.

Ans:

A managed object context (represented by an instance of NSManagedObjectContext) is a temporary ‘scratchpad’ in an application for a (presumably) related collection of objects. These objects collectively represent an internally consistent view of one or more persistent stores.

A single-managed object instance exists in one and only one context, but multiple copies of an object can exist in different contexts.

The key functions of the managed object context include the following:

• Life-cycle management: Here, the context provides validation, inverse relationship handling, and undo/redo.
• Notifications: It refers to context posts’ notifications at various points that can be optionally monitored elsewhere in our application.
• Concurrency: Here, the Core Data uses thread (or serialized queue) confinement to protect managed objects and managed object contexts.

54.What is the difference between atomic- and non-atomic properties? Which is default for synthesized properties? When would you use one over the other?

Ans:

Properties specified as atomic are guaranteed to always return a fully initialized object. This also happens to be the default state for synthesized properties. While it is a good practice to specify atomic properties to remove the potential for confusion, if we leave it off, the properties will still be atomic. This guarantee of atomic properties comes at the cost of performance. However, if we have a property for which we 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 non-atomic can boost the performance.

55.How can you prevent iOS 8 app’s streaming video media from being captured by QuickTime Player on Yosemite during screen recording?

Ans:

HTTP live streams that have their media encrypted will not be recorded by QuickTime Player on Yosemite while screen recording. These will blackout in the recording. HTTP live streaming: It sends live and on‐demand audio and video to iPhone, iPad, Mac, Apple TV, and PC with HTTP live streaming (HLS) technology from Apple. Using the same protocol that powers the web, HLS lets us deploy the content using ordinary web servers and content delivery networks. HLS is designed for reliability and dynamically adapts to network conditions by optimizing playback for the available speed of wired and wireless connections.

56.Does Objective-C contain private methods?

Ans:

No, there is nothing called a private method in Object-C programming. If a method is defined in .m only, then it becomes protected; if it is defined in .h, it is public.

If we really want a private method, then we need to add a local category/unnamed category/class extension in the class and add the method in the category and define it in class.m.

57.What is a plist?

Ans:

Property list or plist refers to a list that organizes data into named values and lists of values using several object types. These types provide us the means to produce data that is meaningfully structured, transportable, storable, and accessible, but still as efficient as possible. Property lists are frequently used by applications running on both Mac OS X and iOS. The property-list programming interfaces for Cocoa and Core Foundation allow us to convert hierarchically structured combinations of these basic types of objects to and from standard XML. We can save the XML data to the disk and later use it to reconstruct the original objects.

The user defaults system, which we programmatically access through the NSUserDefaults class, uses property lists to store objects representing user preferences. This limitation would seem to exclude many kinds of objects, such as NSColor and NSFont objects, from the user defaults system. However, if objects conform to the NSCoding protocol, they can be archived to NSData objects, which are property-list-compatible objects.

58.Explain iOS?

Ans:

Apple Inc created and developed a mobile operating system called iOS (intelligent Operating System).

59.What is the purpose of reuseIdentifier? What is the benefit of setting it into a non-nil value?

Ans:

The reuseIdentifier is used to group together the similar rows in a UITableView, i.e., the rows that differ only in their content, otherwise having similar layouts. A UITableView will normally allocate just enough UITableViewCell objects to display the content visible in the table.

If reuseIdentifier is set to a non-nil value, then the UITableView will first attempt to reuse an already allocated UITableViewCell with the same reuseIdentifier when the table view is scrolled. If reuseIdentifier has not been set, then the UITableView will be forced to allocate new UITableViewCell objects for each new item that scrolls into view, potentially leading to laggy animations.

60.What is the difference between an ‘App ID’ and a ‘Bundle ID’? What is each used for?

Ans:

• 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 strings, with a period (.) separating the two.
• The Team ID is supplied by Apple and is unique to a specific development team, while a Bundle ID is supplied by the developer to match either the Bundle ID of a single app or a set of Bundle IDs of a group of apps.

Since most users consider the App ID as a string, they think it is interchangeable with the Bundle ID. Once the App ID is created in the Member Center, we can only use the App ID prefix that matches the Bundle ID of the application bundle.

The Bundle ID uniquely defines each app. It is specified in Xcode. A single Xcode project can have multiple targets and, therefore, outputs multiple apps. A common use case: an app having both lite/free and pro/full versions or branded multiple ways.

61.What is JSONSerialization ?

Ans:

The  built in way of parsing JSON is called JSONSerialization and it can convert a JSON string into a collection of dictionaries, arrays, strings and numbers .

62.Difference between core  data and sqlite?

Ans:

Core Data is a framework that can be used for managing an object graph. Core Data is not a database.Core Data can use a SQLite database as its persistent store, but it also has support for other persistent store types, including a binary store and an in-memory store. SQLite is a lightweight relational database.

63.Difference between Keychain and NSUserDefaults?

Ans:

In Keychain: If a user removes the app from the device  the saved  UserName and Password still is there.

In NSUserDefaults: If a user removes the app from the device  the saved  UserName and Password are also removed.

64.What is app thinning? How to reduce app size?

Ans:

App thinning is concept of reducing the app size while downloading.Using the below methods we can reduce the app size

1. 1.App Slicing
2. 2.Bitcode
3. 3.On-Demand Resource

65.What is a Bundle ID?

Ans:

The Bundle ID  is the unique string that identifies your application to the system.

66.What are the types of certificates required for developing and distributing apps?

Ans:

Development and distributing certificates.

Development certificate: used for development

Distribution certificates: used for submitting apps to app store or in house

67.What are binaries required to install  the app to devices?

Ans:

.ipa,

.app

68.What are the advantages of Swift over Objective C?

Ans:

• Readability
• Maintenance
• Safer Platform
• Less Code & Less Legacy
• Speed

69.What is the latest xcode version and its features?

Ans:

Xcode latest version is 10.1

• The Dark Mode
• instantly Swift Source Code Editor
• Debugging the Tools
• Playground for Machine Learning
• Source Control

70.What are new features in ios 12 for developers ?

Ans:

• ARKit 2
• Siri Shortcuts
• CarPlay for Navigation Apps
• Health Records
• Natural Language

71.Use of if -let statement in swift

Ans:

By using if- let ,we can unwrap an optional in a safe way, otherwise  nil it may crash the app sometimes.

72.What is id in Objective C?

Ans:

id is a type of any data type. It specifies a reference to any Objective-C object .

73.What are Categories in Objective C?

Ans:

Categories provide the ability to add functionality to an object without changing the actual object.

74.What is Extension in swift?

Ans:

Extension adds new functionality to an existing class, structure, enumeration, or protocol type. Extensions are similar to categories in Objective-C.

75.Define Class methods and instance methods .

Ans:

An instance method  accessed an instance of the class

A class method accessed to the class itself.

76.How to add a swift file to the existing Objective C project?

Ans:

If you add a new swift file to the existing project xcode will ask you to add Objective-C bridging header.

77.What is auto layout and why is it used?

Ans:

Auto Layout is a constraint-based layout system.By using this auto layout developers to create an adaptive interface that responds appropriately to changes in screen size and device orientation.

78.How to pass data between view controllers

Ans:

• Segue, in prepareForSegue method (Forward)
• Delegate (Backward)
• Setting variable directly (Forward)

79.Types of Dispatch Queues

Ans:

Serial :execute one task at a time in the sequential order

Concurrent: execute one or more tasks concurrently.

Main dispatch queue: executes tasks on the application’s main thread.

80.key value coding(KVC) and key value observing (KVO)

Ans:

Key-Value-Coding (KVC) : accessing a property or value using a string.

Key-Value-Observing (KVO) : observe changes to a property or value.

81.Application life cycle

Ans:

• application:willFinishLaunchingWithOptions
• application:didFinishLaunchingWithOptions
• applicationDidBecomeActive
• applicationWillResignActive
• applicationDidEnterBackground
• applicationWillEnterForeground
• applicationWillTerminate

82.Different states of application

Ans:

• Not running
• Inactive
• Active
• Background
• Suspended

83.View life cycle

Ans:

• loadView
• loadViewIfNeeded
• viewDidLoad
• viewWillAppear
• viewWillLayoutSubviews
• viewDidLayoutSubviews
• viewDidAppear
• viewWillDisappear
• viewDidDisappear

84.What is delegate  and notification

Ans:

Delegate: Creates the relationship between the objects. It is one to one communication.

Notification: These are used if an object wants to notify other objects of an event. It is one to multiple communication.

85.What is the significance of “?” in Swift?

Ans:

The question mark (?) is used during the declaration of a property to make a property optional. If the property does not hold a value.

86.What are the Levels of Priority in QOS?

Ans:

• User Interactive
• User Initiated
• Utility
• Background

87.How to write optional values in swift ?

Ans:

An optional that can hold either a value or no value. Optionals are written by appending a ‘?’

88.How to unwrap the optional value in swift ?

Ans:

The simplest way to unwrap an optional value  is to add a ‘!’ after the optional name. This is called “force unwrapping”.

89.What is Method Overloading?

Ans:

It defines a method with the same name many times with different arguments. This kind of feature is known as Method Overloading.

90.What is Method Overriding?

Ans:

If we define a method in a class, and we  know that a subclass might need to provide a different version of the method. When a subclass provides a different implementation of the method defined in a superclass, with the same name, arguments and return type, that is called Overriding. The implementation in the subclass overwrites the code provided in the superclass.

91.What is QOS?

Ans:

QOS – Quality of Service

QOS can be applied all over iOS as well. One can Prioritize queues, thread objects, dispatch queues and POSIX threads.By assigning the correct priority for the work, iOS apps remain quick, snappy and responsive.

92.What is User Interactive?

Ans:

It works on the main thread, Immediately in order to provide a nice user experience. e.g run at while in Drawing and Ui animations.

93.What is User Initiated?

Ans:

It works when the user kicks off and should yield immediate results. It Performs asynchronously that are initiated from the UI  This will get mapped in to the high Priority Global Queue. This work must be complete for the user to continue.

94.What is DeadLock?

Ans:

A deadlock is a situation where two different programs or processes depend on one another for completion, either because both are using. It is the situation where a set of processes are blocked because each process is holding a resource and waiting for another resource acquired by some other process.

95.Define Run Loop?

Ans:

Run loop mode is a collection of input sources and times to be monitored and the collection of run loop observations to be notified.

96.How to define kSomeConstant  ?

Ans:

It is Implicitly defined as an integer. If you want to be more specific you can specify it like above e.g..

97.Define hash value vs raw value ?

Ans:

HashValue:- If you had the enum as we had declared earlier without the type, there is no rawValue available but instead you get a member called hashValue.

RawValue:-  The rawValue on the other hand is a type value that you can assign to the enum members.

98.Define Static Binding and Dynamic Binding?

Ans:

Static Binding: It is resolved at “Compile time” Method overloading is an example of static binding.

Dynamic Binding: It is virtual binding resolved at a “Run Time”. Method overriding is an example of Dynamic Binding