iOS interview questions

1. What is the difference between underscore and self (i.e self.xx and _xx) ?
2. What is property?
3. What is the difference between weak and strong?
4. What is Retain Cycle? And how we can avoid it?
5. What does copy means while declaring a property?
6. What is synthesize and when we need to use it?
7. What is a category?
8. What is an extension?
9. How we can add a property in a category?
10. What is method swizzling and when we should use it?
11. How we can layout subviews in a view?
12. What are the size classes?
13. What is ARC?
14. What is @autorelease and when we should use it?
15. How to animate view with constraint?
16. What is core data?
17. What is core data stack?
18. What is managed object context?
19. How we can do multithreading with core data?
20. How to transfer manage object from one thread to another thread?
21. How to merge changes from one moc to another?
22. Difference between bounds and frame?
23. What does dispatch_once do?
24. What is delegate?
25. How we can do multithreading in iOS?
26. When you will use NSOperations over GCDs and vice versa?
27. What does alloc do?
28. How we can create a class in objective c which don’t inherit from NSObject?
29. What are the different application states in iOS?
30. How we can execute some code when app is in background?
31. How we can wait for some thread to finish before starting another?
32. How you will store user info (username, password or token) securely in iOS?

Thanks to http://www.adnanaftab.com/programming/ios/top-ios-objective-c-interview-questions/