Top 5 Basic iOS Questions Asked in interviews

1.  What is the iPhone?
Answer: 
In this post we will discuss some basic questions and answers before jumping into coding for Application development.

​The iPhone is an integrated cellular telephone and media player developed and marketed by Apple.

It's primary function as a cellular telephone, the iPhone includes a music and video player, digital camera, PDA, and an Internet communications suite.

​The iPhone runs Apple's OS-X operating system iOS.

The first iPhone was unveiled by Steve Jobs, then CEO of Apple, on January 9, 2007, and released on June 29, 2007

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2.What is iPhone SDK?
Answer:

 A software development kit (SDK) released by Apple that allows people to write applications for both the iPhone and the iPod Touch.

The iPhone SDK includes the Xcode IDE, Instruments, iPhone simulator, frameworks and samples, compilers, Shark analysis tool, and more.

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3. What is the difference between drain, release, dealloc and retain in Objective-C?
Answer:

-retain increase the reference count on an object
-release decreases the reference on an object
-drain is used in place of release on ONLY for NSAutoreleasePool objects due to some arcana related to the Objective C garbage collection

-dealloc is called by the system once the retainCount of an object hits 0. It is where you clean up various things your object has (like a deconstructor or finalizer).

You should NEVER call it directly, except for calling [super dealloc] at the end of your dealloc routines.

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4. Class methods vs Instance methods and visibility of methods ?
Answer:

Class methods (most languages use the keyword static)
-Operate on Class variables (they can not access instance variables)
-Do not require an object to be instantiated to be applied
-(+) denotes a class method

Instance methods

-Operate on instances variables and class variables
-Must have an instantiated object to operate on
-(-) denotes an instance method.

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5. how to achieve getter and setter property in iOS?
Answer: 

By using these two preprocessor directives @property and @synthesize we can achieve getter and setter.

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