Most Asked iOS Interview Questions and Answers

iOS Interview Questions and Answers most commonly asked for Experienced PDF, Freshers candidates for Employment.

Describe the functionality of accelerometer of an iPhone ?

iPhone responds to motion using a built-in accelerometer.

The accelerometer detects the movement and changes the display accordingly, at the time of rotating iPhone from portrait to landscape.

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

During app launching, the system creates a main thread for the app and calls the app’s main function on that main thread. The Xcode project’s default main function hands over control to the UIKit framework, which takes care of initializing the app before it is run.

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


What are the requirements for developing iPhone Apps?

Mac OS 10.5/10.6 iPhone SDK (Software Development Kit 3.0/4.0).

IPhone SDK consists of:

IDE to develop iPhone Apps is XCode(This tool is inbuilt in iPhone SDK)

Interface Builder This is used to design GUI of Apps(Inbuilt feature of iPhone SDK)

Instruments  This is used to check any memory leaks in our apps (Inbuilt in SDK)

Simulator This is used to test our apps before deploying into real device.

What is iPhone architecture?

It is similar to Mac OS X architecture

It acts as an intermediary between the iPhone and iPod hardware an the appearing applications on the screen

The user created applications never interact directly with the appropriate drivers, which protects the user applications from changes to the hardware.

Whats fast enumeration?

Fast enumeration is a language feature that allows you to enumerate over the contents of a collection. (Your code will also run faster because the internal implementation reduces

message send overhead and increases pipelining potential.)

Difference between categories and extensions?

Class extensions are similar to categories. The main difference is that with an extension, the compiler will expect you to implement the methods within your main @implementation, whereas with a category you have a separate @implementation block. So you should pretty much only use an extension at the top of your main .m file (the only place you should care about ivars, incidentally) — it’s meant to be just that, an extension.

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

An application behaves differently when running in foreground than in background because of the limitation of resources on iOS devices.

Introduction to iphone application Development?

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.

What are the tools required to develop iOS applications?

iOS development requires Intel-based Macintosh computer and iOS SDK.

Name 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. UIKit framework provides event handling, drawing model, windows, views, and controls specifically designed for a touch screen interface.

What is iPhone OS?

iPhone OS runs on iPhone and iPod touch devices.

Hardware devices are managed by iPhone OS and provides 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.

When an app is said to be in active state?

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

Name the app sate which it reaches briefly on its way to being suspended.

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

Difference between COCOA, COCOA touch and objective C?

Objective C is a dynamic programming language – a bit like C++ and a bit like Java.

Cocoa is the application framework for Mac OS X. Cocoa Touch is the application framework for iPhone and iPod Touch – very similar to Cocoa.

Cocoa is commonly referred to as the combination of the Foundation and AppKit frameworks, while Cocoa Touch is the combination of the Foundation and UIKit frameworks. Cocoa and Cocoa Touch sit on top of other collections of frameworks to create the API stacks. The other layers are Media, Core Services and Core OS. The main difference between Cocoa and Cocoa touch is that the UI classes and APIs aren’t the same as Mac OS X, so instead of NSTextField, you have UITextField. Many of the classes share the same functionality and can be ported quite easily by simply changing the class name, though most will require some more changes, but usually nothing too heavy. There are also some differences between the Foundation frameworks in Cocoa and Cocoa Touch, most commonly missing classes, eg, Cocoa has NSHost and Cocoa Touch doesn’t.

Why iPhone apps are popular?

Give our business a whole new way of transacting business for millions of users.

IPhones are the market leaders in the smart phone segment. The iPhone has become a great device to surf the internet, play games, interact with social networks and transact business.

Multitasking support is available from which version?

iOS 4.0

What are the ways to store data localy on iPhone device?

We store data localy in device through:

1. Plist.

2. NSUserDefaults.

3. SQLite.

4. CoreData.

What is iPhone reference library?

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

When an app is said to be in not running state?

An app is said to be in ‘not running’ state when:

it is not launched.

it gets terminated by the system during running.

Difference between shallow copy and deep copy?

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.

Suppose there are two objects A and B. A is pointing to a different array while B is pointing to different array. Now what I will do is following to do shallow copy.?Char *A = {‘a’,’b’,’c’};?Char *B = {‘x’,’y’,’z’};?B = A;?Now B is pointing is at same location where A pointer is pointing.Both A and B in this case sharing same data. if change is made both will get altered value of data.Advantage is that coping process is very fast and is independent of size of array.

while in deep copy data is also copied. This process is slow but Both A and B have their own copies and changes made to any copy, other will copy will not be affected.

You wish to define your custom view. Which class will be subclassed?

Custom views can be defined by subclassing UIView.

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

UIKit classes should be used only from an application’s main thread.  Note: The derived classes of UIResponder and the classes which manipulate application’s user interface should be used from application’s main thread.

What happens if IApplication object does not handle an event?

In such case the event will be dispatched to your app delegate for processing.


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