Basic iPhone Interview Questions And Answers

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

256bytes.

 

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 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. 

You wish to define your custom view. Which class will be subclassed?
Custom views can be defined by subclassing UIView.   

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).