IOS Development Interview Questions

1. Which are the ways of achieving concurrency in IOS?
Ans:
 The three ways to achieve concurrency in IOS are:

  • Threads
  • Dispatch queues
  • Operation queues

2. 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.

3. How many different annotations available in Objective-C ?
Ans:
Null unspecified, which bridges to a Swift implicitly unwrapped optional. This is the default.

  • Nonnull, the value won’t be nil it bridges to a regular reference.
  • Nullable the value can be nil, it bridges to an optional.
  • Null_resettable the value can never be nil, when read but you can set it to know to reset it. This is only apply property.

4. What’s the difference between the frame and the bounds?
Ans:
 The bounds of a UIView is the rectangle, expressed as a location (x,y) and size (width, height) relative to its own coordinate system (0,0).

The frame of a UIView is the rectangle, expressed as a location (x,y) and size (width, height) relative to the superview it is contained within.

5. Explain About The Major Swift main advantage 

Ans: The major benefits of Swift are well explained here below. 

  •  Optional Types, which make applications crash-resistant
  •  Much faster compared to other languages.
  •  Built-in error handling
  • Closures
  •  Type-safe language
  • It is best known to support pattern matching.

6. 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.

7. What are some pitfalls you’ve experienced with it? Are there any alternatives to MVC?
Ans:
 MVC stands for Model, View, Controller. It is a design pattern that defines how to separate out logic when implementing user interfaces. In iOS, Apple provides UIView as a base class for all _View_s, UIViewController is provided to support the Controller which can listen to events in a View and update the View when data changes. The Model represents data in an application and can be implemented using any NSObject, including data collections like NSArray and NSDictionary.

Some of the pitfalls that people hit are bloated UIViewController and not separating out code into classes beyond the MVC format.

8. What is the Facade Design Pattern?
Ans:
The Facade design pattern furnishes the best known for providing a single interface to a complex subsystem. With the aid of Facade Design Pattern,  In spite of using a user to a group of classes with their APIs, you only compose one simple unified API.

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. 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.

11. What’s the difference between using a delegate and notification?
Ans:
Both are used for sending values and messages to interested parties. A delegate is for one-to-one communication and is a pattern promoted by Apple. In delegation the class raising events will have a property for the delegate and will typically expect it to implement some protocol. The delegating class can then call the _delegate_s protocol methods.

Notification allows a class to broadcast events across the entire application to any interested parties. The broadcasting class doesn’t need to know anything about the listeners for this event, therefore notification is very useful in helping to decouple components in an application.

12. What is Memento Pattern?
Ans:
In Memento Pattern saves your stuff somewhere. Later on, this externalized state can be restored without violating encapsulation; that is, private data remains private. One of Apple’s specialized implementations of the Memento pattern is Archiving other hand iOS uses the Memento pattern as part of State Restoration.

13.what is method swizzling in Objective C and why would you use it?
Ans:
Method swizzling allows the implementation of an existing selector to be switched at runtime for a different implementation in a classes dispatch table. Swizzling allows you to write code that can be executed before and/or after the original method. For example perhaps to track the time method execution took, or to insert log statements.

14. What do you understand by the term NSFetchRequest?
Ans:
Fetch requests are extensively used for fetching predefined objects which match the exact requirement in-relation to individual values, criteria and much more. The main use of this NSFetcherRequest is to fetch from the core data.

15. What is NSURLConnection class? Define its types and use cases?
Ans:
There are two ways of using the NSURLConnection class. One is asynchronous and the other is synchronous.

An asynchronous connection will create a new thread and perform its download process on the new thread. A synchronous connection will block the calling thread while downloading the content and doing its communication.

Many developers think that a synchronous connection blocks only the main thread, which is not true. A synchronous connection will always block the thread from which it is fired. If we fire a synchronous connection from the main thread, the main thread will be blocked. However, if we fire a synchronous connection from a thread other than the main thread, it will be like an asynchronous connection and won’t block our main thread.

In fact, the only difference between synchronous and asynchronous connections is that at the runtime a thread will be created for the asynchronous connection while it won’t do the same for a synchronous connection.

In order to create an asynchronous connection, we need to:

  • Have our URL in an instance of NSString
  • Convert our string to an instance of NSURL
  • Place our URL in a URL Request of type NSURLRequest or, in the case of mutable URLs, in an instance of NSMutableURLRequest
  • Create an instance of NSURLConnection and pass the URL request to it.

16. What is the Responder Chain?
Ans:
 When an event happens in a view, for example a touch event, the view will fire the event to a chain of UIResponder objects associated with the UIView. The first UIResponder is the UIView itself, if it does not handle the event then it continues up the chain to until UIResponder handles the event. The chain will include UIViewControllers, parent UIViews and their associated UIViewControllers, if none of those handle the event then the UIWindow is asked if it can handle it and finally if that doesn’t handle the event then the UIApplicationDelegate is asked.

If you get the opportunity to draw this one out, it’s worth doing to impress the interviewer.

17. 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.

18. What is KVC and KVO? Give an example of using KVC to set a value?
Ans:
KVC stands for Key-Value Coding. It’s a mechanism by which an object’s properties can be accessed using string’s at runtime rather than having to statically know the property names at development time. KVO stands for Key-Value Observing and allows a controller or class to observe changes to a property value.

19. Explain the benefits of the guard?
Ans:
Guard is an advanced aspect of iOS which has is being used extensively. Going deep into the aspects of the guard things will be quite fascinating. There are two major benefits of a guard.

The first benefit of using guard is that it helps in avoiding the Pyramid of Doom. This is very much helpful as it can be seen in the case where the nested statements tend to move further ahead towards the right. 

The other benefit of using the guard is that by making use of the break or return functions it creates an opportunity for an early exit from the loop.

 20. What is the Memento Pattern?
Ans:
In Memento Pattern is effectively employed within the iOS application platform framework. It plays a vital role in saving your stuff somewhere. 

And then, the externalized state can never be taken back else it becomes the violating encapsulation. All the private personal information will be transferred safely.  

One of Apple’s specialized implementations of the Memento pattern is Archiving other hand iOS uses the Memento pattern as part of State Restoration.

21. What is the difference strong, weaks, read only and copy?
Ans:
strong, weak, assign property attributes define how memory for that property will be managed.

Strong means that the reference count will be increased and the reference to it will be maintained through the life of the object

Weak ( non-strong reference ), means that we are pointing to an object but not increasing its reference count. It’s often used when creating a parent child relationship. The parent has a strong reference to the child but the child only has a weak reference to the parent.

  • Every time used on var
  • Every time used on an optional type
  • Automatically changes itself to nil
  • Read-only, we can set the property initially but then it can’t be changed.
  • Copy means that we’re copying the value of the object when it’s created. Also prevents its value from changing.

22. What is the reuseIdentifier used for?
Ans:
 The reuseIdentifier is used to indicate that a cell can be re-used in a UITableView. For example when the cell looks the same, but has different content. The UITableView will maintain an internal cache of UITableViewCell’s with the reuseIdentifier and allow them to be re-used when dequeueReusableCellWithIdentifier: is called. By re-using table cell’s the scroll performance of the tableview is better because new views do not need to be created.

23. 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.

24. Which JSON framework is supported by iOS?
Ans
: 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. 

25. What is the bounding box?
Ans:
 The bounding box is a term used in geometry; it refers to the smallest measure (area or volume) within which a given set of points.

26. What do you understand by the term App Bundle?
Ans:
A bundle can simply be defined as a directory which groups up all the related resources together at one place within the file system. For example, if you build an iOS app, Xcode packages then it can be called as a bundle. Inside an iOS app bundle, it contains all the applications files which can be executable. App Bundle also supports the resource different files which include localized content, image files and app icons. These elements help in delivering the best application performance to the iOS software.

27. Differentiate between the concepts of viewDidLoad and viewDidAppear?
Ans:
When the view has loaded the function which is called is viewDidLoad. This can be done either from a Xib file, or any programmatically created in lead View. 

ViewDidAppear can be called anytime whenever the view is presented on the device. Depending on the case of your data you can decide which function to be used.

28. Which is the framework that is used to construct 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.

29. What’s Completion Handler?
Ans:
 Completion handlers are super convenient when our app is making an API call, and we need to do something when that task is done, like updating the UI to show the data from the API call. We’ll see completion handlers in Apple’s APIs like dataTaskWithRequest and they can be pretty handy in your own code.

The completion handler takes a chunk of code with 3 arguments:(NSData?, NSURLResponse?, NSError?) that returns nothing: Void. It’s a closure.

The completion handlers have to marked since they are executed some point after the enclosing function has been executed.

 30. How to pass data between view controllers?
Ans:
 There are 3 ways to pass data between view controllers.

Segue, in prepareForSegue method (Forward)

Delegate (Backward)

Setting variable directly (Forward). 

31. What is NSOperation , NSOperationQueue ,NSBlockOperation?
Ans:
 NSOperation adds a little extra overhead compared to GCD, but we can add dependency among various operations and re-use, cancel or suspend them.

NSOperationQueue, It allows a pool of threads to be created and used to execute NSOperations in parallel. Operation queues aren’t part of GCD.

NSBlockOperation allows you to create an NSOperation from one or more closures. NSBlockOperations can have multiple blocks, that run concurrently.

32. 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

33. 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.

34. 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.

35. What is the difference between viewDidLoad and viewDidAppear?
Ans:
 viewDidLoad is called when the view is loaded, whether from a Xib file, storyboard or programmatically created in loadView. viewDidAppear is called every time the view is presented on the device. Which to use depends on the use case for your data. If the data is fairly static and not likely to change then it can be loaded in viewDidLoad and cached. However if the data changes regularly then using viewDidAppear to load it is better. In both situations, the data should be loaded asynchronously on a background thread to avoid blocking the UI.

36. How would you securely store private user data offline on a device? What other security best practices should be taken?
Ans:
 Again there is no right answer to this, but it’s a great way to see how much a person has dug into iOS security. If you’re interviewing with a bank I’d almost definitely expect someone to know something about it, but all companies need to take security seriously, so here’s the ideal list of topics I’d expect to hear in an answer.

If the data is extremely sensitive then it should never be stored offline on the device because all devices are crackable.

The keychain is one option for storing data securely. However it’s encryption is based on the pin code of the device. User’s are not forced to set a pin, so in some situations the data may not even be encrypted. In addition the users pin code may be easily hacked.

A better solution is to use something like SQLCipher which is a fully encrypted SQLite database. The encryption key can be enforced by the application and separate from the user’s pin code.

Other security best practices are:

  • If possible implement certificate pinning in the application to prevent man-in-the-middle attacks on public WiFi.
  • Clear sensitive data out of memory by overwriting it.
  • Ensure all validation of data being submitted is also run on the server side.

 37. Explain about the layer objects and where do they present?
Ans:
 Layer objects are one among the simple application elements that are delivered to perform various applications. In general layer, objects can be interpreted as the data objects that represent visual content. These layer objects will help the views to render their content. The best feature if this is that custom layer objects can be created and get them added to the interface to perform complex animations and other such related highly sophisticated visual effects.

38. Explain the concept of SQLite limits?
Ans:
 SQLite Limits is one among the most advanced development concepts of iOS application platform. The in-depth functioning aspects of SQLite Limits include

  •  At first defining the relations between the tables is quite necessary. 
  •  Then work on defining the schema of all the tables.
  •  Then all the queries must be manually written in order to fetch the data. 
  •  We need to query results and then map those to models.
  • Queries are very fast

39. What is Enum or Enumerations?
Ans:
According to Apple’s Swift documentation:

Managing state, the bits of data that keep track of how the app is being used at the moment, is an important part of a developing your app. Because enumerations define a finite number of states, and can bundle associated values with each individual state, you can use them to model the state of your app and its internal processes.

Enum is a type that basically contains a group of related values in the same umbrella but case-less enum won’t allow us to create an instance.

40. What is SpriteKit and what is SceneKit?
Ans:
 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.

41. How to Prioritize Usability in Design ?
Ans:
 Broke down its design process to prioritize usability in 4 steps:

Think like the user, then design the UX.

Remember that users are people, not demographics.

When promoting an app, consider all the situations in which it could be useful.

Keep working on the utility of the app even after launch.

42. What is Singleton Pattern ?
Ans:
 The Singleton design pattern ensures that only one instance exists for a given class and that there’s a global access point to that instance. It usually uses lazy loading to create the single instance when it’s needed the first time.

43.  Explain MVVM?
Ans:
UIKit independent representation of your View and its state. The View Model invokes changes in the Model and updates itself with the updated Model, and since we have a binding between the View and the View Model, the first is updated accordingly.

Your view model will actually take in your model, and it can format the information that’s going to be displayed on your view.

There is a more known framework called RxSwift. It contains RxCocoa, which are reactive extensions for Cocoa and CocoaTouch

44.  How to pass a variable as a reference?
Ans:
We need to mention that there are two types of variables: reference and value types. The difference between these two types is that by passing value type, the variable will create a copy of its data, and the reference type variable will just point to the original data in the memory.

45. What is Grand Central Dispatch (GCD)?
Ans:
 GCD is a library that provides a low-level and object-based API to run tasks concurrently while managing threads behind the scenes. Terminology;

Dispatch Queues, A dispatch queue is responsible for executing a task in the first-in, first-out order.

Serial Dispatch Queue A serial dispatch queue runs tasks one at a time.

Concurrent Dispatch Queue A concurrent dispatch queue runs as many tasks as it can without waiting for the started tasks to finish.

Main Dispatch Queue A globally available serial queue that executes tasks on the application’s main thread.

46. Explain Swift’s pattern matching techniques?
Ans:
 Tuple patterns are used to match values of corresponding tuple types.

Type-casting patterns allow you to cast or match types.

Wildcard patterns match and ignore any kind and type of value.

Optional patterns are used to match optional values.

Enumeration case patterns match cases of existing enumeration types.

Expression patterns allow you to compare a given value against a given expression.

47. 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.

What considerations do you need when writing a UITableViewController which shows images downloaded from a remote server.

This is a very common task in iOS and a good answer here can cover a whole host of knowledge. The important piece of information in the question is that the images are hosted remotely and they may take time to download, therefore when it asks for “considerations”, you should be talking about:

Only download the image when the cell is scrolled into view, i.e. when cellForRowAtIndexPath is called.

Downloading the image asynchronously on a background thread so as not to block the UI so the user can keep scrolling.

When the image has downloaded for a cell we need to check if that cell is still in the view or whether it has been re-used by another piece of data. If it’s been re-used then we should discard the image, otherwise we need to switch back to the main thread to change the image on the cell.

Other good answers will go on to talk about offline caching of the images, using placeholder images while the images are being downloaded.

48. What considerations do you need when writing a UITableViewController which shows images downloaded from a remote server?
Ans:
 This is a very common task in iOS and a good answer here can cover a whole host of knowledge. The important piece of information in the question is that the images are hosted remotely and they may take time to download, therefore when it asks for “considerations”, you should be talking about:

Only download the image when the cell is scrolled into view, i.e. when cellForRowAtIndexPath is called.

Downloading the image asynchronously on a background thread so as not to block the UI so the user can keep scrolling.

When the image has downloaded for a cell we need to check if that cell is still in the view or whether it has been re-used by another piece of data. If it’s been re-used then we should discard the image, otherwise we need to switch back to the main thread to change the image on the cell.

Other good answers will go on to talk about offline caching of the images, using placeholder images while the images are being downloaded.

49. What do you understand by the term NS Persistent Container?
Ans:
 NSPersistentContainer can be interpreted as property which has been developed in order to create and return a container which has loaded the store for the application to it. Actually, this is a critical process to get done and it may fail to deliver legitimate error conditions.

50. In the case of iOS application getting crashed what are the things you are going to do?
Ans:
 It is quite obvious in seeing the applications getting crashed and the performance goes down. In such cases the sequential steps which are done to find the best solution to the mentioned problem are

  • At first, get the exact steps to reproduce the crashed application.
  •  Then the next thing to be done is to find out the iOS version of that particular device.
  • Then check if the version is latest or not?
  • And at the end try to get device logs if possible.

51. Differentiate the concepts of copy and retain?
Ans:
 Retaining in the sense relates to the aspect in which the total count increases by one. This states that the instance of the object will be kept in memory unless it retains count totally drops to the value of null or zero. 

Whereas, the term Copy indicates that the object will be cloned with duplicate values.

52. What are the benefits of Relam?
Ans:
 Relam is considered to be one among the best iOS platform. The benefiting aspects of this concept are

  • An open-source database framework.
  • Implemented from scratch.
  •  Zero-copy object store.
  • Fast.

53. What do you understand by the term NS Fetched Results Controller?
Ans:
 NSFetchedResultsCounter is a most liked part by the developers as it makes their lives by simply abstracting away much of the coding part which is used to synchronize a table view that has a data source backed by a core data. Though it is a controller it’s not a view controller and has no user interface.

54. Which are the app’s state transitions when it is launched?
Ans:
 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.

55. 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.

56. 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.

57. What is ABI?
Ans:
ABIs are important when it comes to applications that use external libraries. If a program is built to use a particular library and that library is later updated, you don’t want to have to re-compile that application (and from the end user’s standpoint, you may not have the source). If the updated library uses the same ABI, then your program will not need to change. ABI stability will come with Swift 5.0

58. What is Decorator Design Pattern?
Ans:
 The Decorator pattern dynamically adds behaviors and responsibilities to an object without modifying its code. It’s an alternative to subclassing where you modify a class’s behavior by wrapping it with another object.

59. Explain generics in Swift ?
Ans:
 Generics create code that does not get specific about underlying data types. Don’t catch this article. Generics allow us to know what type it is going to contain. Generics also provides optimization for our code.

60. Why is design pattern very important ?
Ans:
Design patterns are reusable solutions to common problems in software design. They’re templates designed to help you write code that’s easy to understand and reuse. Most common Cocoa design patterns:

  • Creational: Singleton.
  • Structural: Decorator, Adapter, Facade.
  • Behavioral: Observer, and, Memento.

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