iOS Interview Questions

How would you create your own custom view?


Diff between @class & #import?


What’s fast enumeration?



What is self? Can we change / assign another value to self?


Hierarchy for UIWindow, UIButton, UIView, UIViewController& UIWindow?





What’s a struct& Union?



What is a class?Difference between a class and a structure?

What’s the difference between NSArray and NSMutableArray?

Which is faster: to iterate through an NSArray or an NSSet?

Bag (collection type) in iOS?

Explain retain counts.

What the difference is between retain & assign?

What the difference is between retain & copy?

Is a delegate retained?

Outline the class hierarchy for a UIButton until NSObject.

What is dynamic?

What are selectors in iOS & how they work?

If I call performSelector: withObject: afterDelay: – is the object retained?

How would you check to see if it responds to a given message/selector?

Can you explain what happens when you call autorelease on an object?

When will be the autorelease object released?

Ball *ball = [[[[Ball alloc] init] autorelease] autorelease];

Implement the following methods: retain, release, autorelease.

Consider we are implementing our own thread with lot of autoreleased object. Is it mandatory to use autorelease pool on this scenario if yes/no why?

What is the first thing to do on a thread (autorelease pool)

What’s the NSCoder & NSCoding protocol?

What’s an NSOperationQueue and how/would you use it?–mobile-14993

What is a block and how is it used?

Explain the difference between NSOperationQueue concurrent and non-concurrent.


Explain the correct way to manage Outlets memory.

Is the delegate for a CAAnimation retained?

Explain the animations used for UIView?

Implement your own synthesized methods for the property NSString *title.

Explain how code signing works.

Explain the steps involved in submitting the App to App-Store.

What are all the newly added frameworks iOS ?

What are the App states? Explain them?

How can you respond to state transition?

Explain the options and bars available in xcode 4.2/4.0 workspace window?

What is Automatic Reference Counting (ARC)?

Is return object in arc is autorelease?

Multitasking support is available from which version?

Explain multitasking in iOS.

What is push notification? How it works?

How many bytes we can send to apple push notification server.

Why dynamic memory allocation is required?

Can you just explain about memory management in iOS?

Why do we need to use @Synthesize?

What are categories in iOS?

What is Delegation in iOS?

How can we achieve singleton pattern in iOS?

What is delegate pattern in iOS?

What is NSNotification in iOS?

What is the difference between delegates and notifications?

Explain the types of Notification in iPhone? And how to use them?

What is posing in iOS?

What is atomic and nonatomic? Which one is safer? Which one is default?

What is the configuration file name in iOS explain in brief? (Or) What is plist file and explain about it is usage?

What is the difference between copy & retain? When can we go for copy and when can we go for retain?

What is difference between copy & mutable copy?

What is difference between shallow copy & deep copy?

Have you ever used automated unit test framework in iOS? Explain in short?

What are all the difference between iOS3, iOS4, iOS5, iOS6 & iOS7?

Is there any garbage collector concept available in iOS?

What is difference between synchronous and asynchronous in web request?

Project architecture for service calls & xml / json parsing?

What are all the instruments available in Xcode?

Explain method swizzling. When you would use it?

Take three objects: a grandparent, parent and child. The grandparent retains the parent, the parent retains the child and the child retains the parent. The grandparent releases the parent. Explain what happens.

What happens when you invoke a method on a nil pointer?

Give two separate and independent reasons why retainCount should never be used in shipping code.

Explain your process for tracing and fixing a memory leak.

Explain how an auto release pool works at the runtime level.

In C, how would you reverse a string as quickly as possible?

What is the difference between frames and bounds?

What is the MVC software architecture pattern?

What’s the difference between a xib and a storyboard?

What is Core Data?

Difference between Core Data and Database / SQLite.

Steps for using Core Data?

Describe Waterfall and Agile methodologies.

What is Protocol in objective c?

Difference between protocol and delegate?

Difference between UiTableView & UIPickerView?

Explain Delegate methods for NSUrlConnection & UITableViewDeleagate?

What is difference between delegate & data source?

Explain Mapkit, UIkit, foundation frameworks.

Explain UIViewControllers lifecycle.

Difference between UIView & UIViewController?

Explain Threads.

What is difference between SAX & DOM parser?

What is json & jsonp?

Which JSON framework is supported by iOS?

What is the difference between synchronous & Asynchronous?

What is Weak & strong in iOS?

Where can you test Apple iPhone apps if you don’t have the device?

Name the application thread from where UIkit classes should be used?

Why an app on iOS device behaves differently when running in foreground than in background?

How can an operating system improve battery life while running an app?

Who calls the main function of you app during the app launch cycle?

What is the use of controller object UIApplication?

What is the purpose of UIWindow object?

Which object manages presentation of app’s content on the screen?

What are layer objects and what do they represent?

What are the design patterns in iOS?

What are all the difference between categories and subclasses? Why should we go to subclasses?

What Is Extensions In Objective C?Extensions vs Category?

What are KVO and KVC?

Does KVO work with ivars too?

What is polymorphism & inheritance& encapsulation?

What are composite objects?

What is responder chain?

InApp purchase product type

The advantages and disadvantages about synchronous versus asynchronous connections.

What is the split view controller?

What is the navigation controller?

Objective-C vs. C/C++

Class Introspection

Explain proxy class.

Formal vs. informal protocol.

Optional vs. required?

Explain event loop.

Explain Threadsafe.

Explain GCD.

Explain callbacks.

Are Document objects required for application? What do they offer?

What is iPhone reference library?

Difference between COCOA & COCOA touch?

How to edit the pdf?

How to convert UIView to PDF?

How to display different image from the server inside the table view?

Given an object of an unknown type, how would you determine its class? How would you check to see if it conforms to a given protocol?

Explain stack and heap?

Write a program, if u have two classes A and B. A contain some class and instance method and you have to invoke this method in B. Do it without using inheritance?

Dynamic polymorphism in iOS?

Overloading & overriding?

Write a simple program to parse an xml file (xml file structure will be provided by the company)

Steps to use SQLite in a project?

Write a simple program to add data using SQLITE?

Difference between pass by value and pass by reference

What is Xcode and iPhone SDK?

What is a memory warning, how do we respond to it

Small task: explain how to download an image from the internet, and show this in an image view – all this after a button is tapped on the view

How to download a file from the internet?

What is a run loop, and one very common place where it is used (timers, NSUrlConnection)

How to start a thread

How to start a selector on a background thread

What to do when the selector has more parameters (NSInvocation)

How to delay executing a selector

What happens here (compile + runtime): NSString *s = [NSNumber numberWithInt: 3]; int i = [s intValue];

Pro and cons of using the type id

How to fake multiple class inheritance

Root classes: NSObject, NSProxy

isKindOfClass isMemberOfClass

Ask about the Isa member

Class methods vs. instance methods.

What to do in a situation when a class doesn’t implement a method from a protocol?

Main difference between java interface and protocols.

Designated initializers

Challenges in ios7 porting

Autolayout and storyboard

Content Hugging Priority
Content Compression Resistance Priority

Sql vs coredata

Coredata migrations & multiple contexts
Can we use multiple coredatamodel
Coredata in background or asynchronous

Offline data caching

Multiple requests using nsurlconnection

Certificates in iOS

cert pinning

SSL Pinning

Encryption / Encoding / Hashing / Obfuscation:

Authorization vs Authentication:


Types Authentication

Http / Https


Http 1.x / Http 2.0




design patterns & design principles

class introspection
cryptography types
symmetric / assymetric crypto


SOLID principle & design patterns

buffer overflow / underflow
disallow singleton class to call init

abstraction encapsulation
protected in ios
multilevel and multiple inheritance have you tried
storyboard autolayout / size classes iphone and ipad
singleton what if user create alloc init object
asynchronous request on table scroll for image
coredata is stack based or queue based? what is stack?
core data migration
design patterns & design principles
localization? how to replace localization file on locale change?
localization in storyboard, xib, plist?
change images on basis of localization?
profile & certification? what is code signing?
APNS flow?
algorithm for core data data migration?
rest & soap?
@synchronized in methods?
what are static classes?
abstract classes in ios? can we create object of abstract class?
what are virtual methods? (C++)
cross platforms pros cons?
abstract factory & factory classes?
write project for lazy loading.
mvc vs mvvm?

Collection views
Size classes



NSUser defaults



library vs Frameworks

static vs dynamic library


ibeacon , how it works, which fremeworks to use & implementation.

All HTTP methods & differences
Autolayout in scroll view

Reactive COCOA

COCOA Core competencies-


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