iOS interview Questions

I have seen lots of peoples asking on web about iOS interview questions. So I decided to gather up a list of iOS interview questions that could serve as a good starting point for Objective-C and Cocoa development topics. Also I intend to update this list later when i will have more information to add – hoping to build a comprehensive list of technical questions.
So here I am with a list of possible iOS interview questions:

—- Objective-C related —-

• identify basic OO concepts and the keywords Objective-C uses (interface, implementation, property, protocol, etc)
• what is a designated initializer, what is the pattern for the initializers and why ( if (self = [super ...] ) )
• basic memory management topics, like ownership retain/release/autorelease
  • what happens if you add your just created object to a mutable array, and you release your object
  • what happens if the array is released
  • what happens if you remove the object from the array, and you try to use it
• trick: garbage collection on iPhone
• autorelease pool usage
• property declarations ( assign, nonatomic, readonly, retain, copy )
  • trick: ask about the nonexistent atomic keyword, what does atomic mean
  • ask on how to correctly implement a retaining setter property
  • ask about the circular reference problem and delegates being usually saved with assign rather then retain
• what is the difference between the dot notation and using the square brackets
  • what happens when we invoke a method on a nil pointer
  • difference between nil and Nil
• what is KVO and related theory + methods to use when observing
  • does KVO work with ivars too?
• protocols – maybe: main difference between c#/java interface and protocols
  • what to do in a situation when a class doesn’t implement a method from a protocol
• what about multiple class inheritance
• what is fast enumeration
• class methods vs instance methods
  • visibility of methods
• what is an actual class in Objective-c (struct)
  • ask about the isa member
  • ask about isKindOfClass isMemberOfClass
• root classes: NSObject, NSProxy
  • how does proxy-ing work
  • how to fake multiple class inheritance
• id type
  • what happens during compilation if we invoke a method on an variable with the type id
  • what happens runtime if the method exists
  • what happens if the methods doesn’t exist
  • pro and cons of using the type id
  • what happens here(compile + runtime): NSString *s = [NSNumber numberWithInt:3]; int i = [s intValue];
• what are class categories and the () category
• what is an informal protocol
• what is a delegate, how to create one, and use one
• what is a selector, how to do a perform selector
  • how to delay executing a selector
  • what to do when the selector has more paramters (NSInvocation>
  • how to start a selector on a background thread
• how to start a thread
  • what is the first thing to do on a thread (autorelease pool)
  • what is a runloop, and one very common place where it is used (timers, nsurlconnection)
• how to download something from the internet
  • what is the difference between a synchronous and an asynchronous request
  • 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
• what are notifications, how to use them
• what is a memory warning, how do we respond to it

—- A bit more advanced topics —-

• when to use retainCount (never, and why)
• why shouldn’t we invoke instance methods in an initializer and the dealloc
• NSCoding, archiving
• NSCopying, why can’t we simply use our own objects as key in a dictionary, what to do to solve the problem ( and the difference between a shallow and a deep copy)

—- UIKit related —-

• what is a view, and a window
• difference between a view’s bounds and frame
• what is the resolution of the current available devices, difference between points and pixels (starting with iOS4)
• what is the responder chain, becomeFirstResponder
• what do IBOutlet and IBAction mean, what are they preprocessed to
• how do tableviews function
• what about multithreading and UIKit
• what to do when the keyboard appears and hides some parts of the UI that are important
• why should we release the outlets in viewDidUnload
• what is awakeFromNib, what is the difference between a nib and a xib

—- CoreData —-

• what is a context
• what about multi threading and core data usage
• what is an NSManagedObjectId – can we save it for later if the application was stopped
• what types of stores does core data support
• what is lazy loading, how does this relate to core data, situations when this can be handy
• how to ready only a few attributes of an entity
• what is an fetch result controller
• how to synchronize contexts
• how could one simulate an NSManagedObject (i’m thinking of the fact that all the properties are dynamic and not synthesized)

Okay – this probably is not a very organized list nor it is complete, but as i said i will get back and complete this list.
Also i would be really glad if you would drop a comment if you find this list useful, or want to add / correct something.