Top most asked iOS Question interview

1. What is category? Can you have properties or ivars in a category?
2. What is the output binary format? Explain .app structure.
3. What are the CPU architectures supported by iOS devices?
4. What iOS version onwards ARC can be used?
5. Can we support same application for iPhone3GS and iPhone5? Why not?
6. Can I write some C++ function in same .m file? Will it compile? If no, what changes should I do to compile it?
7. What are the types of iOS binaries you can create using XCode? (.app, .ipa, .a, .framework)
8. Can a static library (.a) contain resources like images, sound files etc?
9. What is bundle?
10. Explain application life cycle.
11. What is responder chain?
12. Tell me hierarchy of UIButton.
13. Why create a custom view?
14. Why UIControl is provided if we can create custom UIView?
15. What are lifecycle events of UIViewController?
16. Difference between viewDidLoad and viewDidAppear?
17. Is UIKit thread safe?
18. Why do we override drawRect: method?
19. What are layers?
20. What are various singleton instances provided by frameworks? (UIApplication, NSFileManager, NSUserDefaults, etc.)
21. What is NSUserDefaults? What type of data can we store there?
22. How do you check if your code has memory leaks?
23. What does static analyser do?
24. What are different Instruments Xcode supports for app profiling?
25. Concepts of notification center, local and remote notifications.
26. Have you uploaded app on Appstore? What is the process?
27. Difference between Developer and Enterprise Developer accounts?
28. Common reasons for app rejection from Appstore review process?
29. UITableView cell reuse. How to get it working (w/ or w/o XIB)? How would you implement reuse on a UIScrollView?
30. What is protocol? What is formal and informal protocol?
31. What is ARC? Is it garbage collection?
32.  Difference between atomic and nonatomic properties?
33.  Difference between strong and retain?
34. What is delegate? Can delegates be retained?
35.  What is retain cycle?
36.  Does ObjectiveC have multiple inheritance? Why not? How to imitate multiple inheritance?
37.  What is class extension? Why do we require them?
38.  Who calls dealloc method? Can we implement dealloc in ARC? If yes, what is the need to do that?
39.  Can you write setter method for a retain property?
40.  Can you write a singleton class in ObjectiveC?
41.  What is GCD? What are advantages over NSThread?
42.  What is NSOperation and NSOperationQueue?
43.  What are NSAutoreleasePool? When to use them?
44.  How does dispatch_once manages to run only once?
45. What are blocks?
46.  Does a thread created using performSelectorInBackground:withObject: creates its own autorelease pool?
47.  ObjectiveC is dynamic language? True/False, explain.
48. Explain UIApplicationMain?
49.  What is the output binary format? Explain .app structure.