iOS Interview Questions and Answers for Freshers

1. What is iPhone?

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

2.What is an iPhone app?

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

3. 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.

4. Multitasking support is available from which version?

iOS 4.0

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

256bytes.

6. What are the features of iPhone 3gs?

• Video: Videos can be edited, shared. High quality VGA video can be shot in portrait or landscape.
• 3 Mega pixel 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 Iphon3 with Mac notebook or laptop.

7. 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.

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

iOS Simulator can be used to test mobile applications. 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.

9. Does iOS support multitasking? 


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

10. Which JSON framework is supported by iOS? 

SBJson framework is supported by iOS.  It is a JSON parser and generator for Objective-C. SBJson provides flexible APIs and additional control that makes JSON handling easier.

11. 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.

12. 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.

13. 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.

14. What are the popular apps of iPhone?

• Face book-Social networking
• Doodle Buddy-drawing
• Pandora Radio-radio on our iPhone
• Yelp-restaurant reviews

15. 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.

16. What is iPhone sdk?

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.

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.

What are the location services?

Applications such as Maps, camera and compass are allowed to use the information from cellular, Wi-Fi and Global Positioning System networks for determining the approximate locations.

The location is displayed on the screen, using a blue marker.

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.

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. 

Which API is used to write test scripts that help in exercising the application's user interface elements? 


UI Automation API is used to automate test procedures. Tests scripts are written in JavaScript to the UI Automation API.  This in turn simulates user interaction with the application and returns log information to the host computer.

Explain about the applications that can be used with iPhone ?

Technology, Entertainment and Design (TED): Allows to watch and listen to world’s most fascinating people have to say, all on the iPhone.

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 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.

What are sensors in iPhone?

The proximity sensor immediately turns off the display when the iPhone is lifted to ear. With this sensor the power is saved and accidental dialing is prevented.

The display is automatically brightens the iPhone by the ambient light sensor when the sunlight or bright rooms and dims in darker places.

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


An app is notified whenever the operating system moves the apps between foreground and background.  The operating system improves battery life while it bounds what your app can do in the background. This also improves the user experience with foreground app.

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.

Which framework delivers event to custom object when app is in foreground? 


The UIKit infrastructure takes care of delivering events to custom objects. As an app developer, you have to override methods in the appropriate objects to process those events.

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.

Assume that your app is running in the foreground but is currently not receiving events. In which sate it would be in?
 
An app will be in InActive state if it is running in the foreground but is currently not receiving events. An app stays in InActive state only briefly as it transitions to a different state.

How can you respond to state transitions on your app? 


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

For example: 

applicationDidBecomeActive method can be used to prepare to run as the foreground app. 
applicationDidEnterBackground method can be used to execute some code when app is running in the background and may be suspended at any time.
 
applicationWillEnterForeground method can be used to execute some code when your app is moving out of the background 
applicationWillTerminate method is called when your app is being terminated.

List down app's state transitions when it gets launched. 


Before the launch of an app, it is said to be in not running state.
When an app is launched, it moves to the active or background state, after transitioning briefly through the inactive state.

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.

Give example scenarios when an application goes into InActive state? 


An app can get into InActive state when the user locks the screen or the system prompts the user to respond to some event e.g. SMS message, incoming call etc.

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.

Assume that an app is not in foreground but is still executing code. In which state will it be in? 


Background state.

An app is loaded into memory but is not executing any code. In which state will it be in? 


An app is said to be in suspended state when it is still in memory but is not executing any code.

Assume that system is running low on memory. What can system do for suspended apps? 


In case system is running low on memory, the system may purge suspended apps without notice.

What is the use of controller object UIApplication?

Controller object UIApplication is used without subclassing to manage the application event loop. It coordinates other high-level app behaviors. 
It works along with the app delegate object which contains app-level logic.

How is the app delegate is declared by Xcode project templates?

App delegate is declared as a subclass of UIResponder by Xcode project templates.

What happens if IApplication object does not handle an event?

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

Which app specific objects store the app's content?

Data model objects are app specific objects and store app’s content. Apps can also use document objects to manage some or all of their data model objects.

Are document objects required for an application? What does they offer?

Document objects are not required but are very useful in grouping data that belongs in a single file or file package.

How do you change the content of your app in order to change the views displayed in the corresponding window?

To change the content of your app, you use a view controller to change the views displayed in the corresponding window. Remember, window itself is never replaced.

Define view object.

Views along with controls are used to provide visual representation of the app content. View is an object that draws content in a designated rectangular area and it responds to events within that area.

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

Custom views can be defined by subclassing UIView.

Which object is create by UIApplicationMain function at app launch time?

The app delegate object is created by UIApplicationMain function at app launch time. The app delegate object's main job is to handle state transitions within the app.

Which object manage the presentation of app's content on the screen?

View controller objects takes care of the presentation of app's content on the screen. A view controller is used to manage a single view along with the collection of subviews. It makes its views visible by installing them in the app’s window.

Which is the super class of all view controller objects?

UIViewController class. The functionality for loading views, presenting them, rotating them in response to device rotations, and several other standard system behaviors are provided by UIViewController class.

What is the purpose of UIWindow object?

The presentation of one or more views on a screen is coordinated by UIWindow object.

Apart from incorporating views and controls, what else an app can incorporate?

Apart from incorporating views and controls, an app can also incorporate Core Animation layers into its view and control hierarchies.

What are layer objects and what do they represent?

Layer objects are data objects which represent visual content. Layer objects 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.

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.

What are KVO and KVC?

KVC: Normally instance variables are accessed through properties or accessors but KVC gives another way to access variables in form of strings. In this way your class acts like a dictionary and your property name for example “age” becomes key and value that property holds becomes value for that key. For example, you have employee class with name property.

You access property like

NSString age = emp.age;

setting property value.

emp.age = @”20″;

Now how KVC works is like this

[emp valueForKey:@"age"];

[emp setValue:@"25" forKey:@"age"];

KVO : The mechanism through which objects are notified when there is change in any of property is called KVO.

For example, person object is interested in getting notification when accountBalance property is changed in BankAccount object.To achieve this, Person Object must register as an observer of the BankAccount’s accountBalance property by sending an 

addObserver:forKeyPath:options:context: message.

What is difference between NSNotification and delegate?

Delegate is passing message from one object to other object. It is like one to one communication while nsnotification is like passing message to multiple objects at the same time. All other objects that have subscribed to that notification or acting observers to that notification can or can’t respond to that event. Notifications are easier but you can get into trouble by using those like bad architecture. Delegates are more frequently used and are used with help of protocols.

What is push notification?

Imagine, you are looking for a job. You go to software company daily and ask sir “is there any job for me” and they keep on saying no.  Your time and money is wasted on each trip.(Pull Request mechanism).

So, one day owner says, if there is any suitable job for you, I will let you know. In this mechanism, your time and money is not wasted. (Push Mechanism).

What is Automatic Reference Counting (ARC) ?

ARC is a compiler-level feature that simplifies the process of managing the lifetimes of Objective  C objects. Instead of you having to remember when to retain or release an object, ARC evaluates the lifetime requirements of your objects and automatically inserts the appropriate method calls at compile time.

What is polymorphism?

This is very famous question and every interviewer asks this. Few people say polymorphism means multiple forms and they start giving example of draw function which is right to some extent but interviewer is looking for more detailed answer.

Ability of base class pointer to call function from derived class at runtime is called polymorphism.

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.)

Whats a struct?

A struct is a special C data type that encapsulates other pieces of data into a single cohesive unit. Like an object, but built into C. 

Whats the difference between frame and bounds?

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