What is the difference Between APPKit and UIKit?

AppKit
AppKit is included in the OS X SDK only.It provides all the classes and controls you need for creating Mac applications.Most of these classes share a common naming prefix starts with NS and classes you will be working with include - 

UIKit

UiKit is the framework that iOS uses to provide its UI and its classes         start with a UI prefix. For example, both frameworks have a class to         represent color include UIColor,while other concepts are pretty       unique to UIKit, such as its use of predefined controllers such as               UINavigationController and UITabBarController - 

What is the difference b/w loadview and viewdidload ? 

oadView

loadView is called by the view controller to load the view. It is the active action of creating and instantiating the UIView object. This is where the   view controller decides how the view should look based on what it         knows from the storyboard.

viewDidLoad

viewDidLoad is called after loadView has completed all its tasks and the UIView is ready for display. It is where you initialize any properties of     the view or the view controller object and finalize them before                 viewWillAppear is called.

If you are using storyboard, you would almost never use loadView. Even if you do, most of the initialization of different properties of the view        should be done in viewDidLoad, as stated in the Apple documentation.  - See more at: http://huntmyideas.weebly.com/blog/ios-interview-questions-and-answers-part-6#sthash.3NexgFV7.dpuf