Why NSString, NSDictionary, etc starts with NS?

Most Cocoa classes begin with NS since they were initiated under NeXTStep.

Objective-C

Objective-C is a superset of the C language.

@interface

An interface is where you define the attributes and operations of class.

Function vs Method

An Objective-C method is just a C function with two arguments always present at the beginning.

Objective-C method

[someObject aMethod];

Is exactly equivalent to the C function

objc_msgSend(someObject, @selector(aMethod));

 

Foundation Framework vs Core Foundation Framework

CoreFoundation is written in C while Foundation is written in Objective-C.

Core OS Layer

1. System
2. ExternalAccessory
3. Accelerate
4. CoreBluetooth
5. Security

Core Services Layer

1. Social
2. Accounts
3. PassKit
4. StoreKit
5. EventKit
6. NewsstandKit
7. AdSupport
8. AddressBook
9. Foundation
10. CoreFoundation
11. CoreData
12. CoreMedia
13. CoreLocation
14. CoreMotion
15. CoreTelephony
16. MobileCoreServices
17. QuickLook
18. CFNetwork
19. SystemConfiguration
20. UIAutomation

Media Layer

1. CoreText
2. CoreImage
3. CoreAudio
4. CoreVideo
5. AVFoundation
6. AssetsLibrary
7. AudioToolbox
8. AudioUnit
9. CoreGraphics
10. CoreMIDI
11. GLKit
12. ImageIO
13. MediaPlayer
14. OpenAL
15. OpenGLES
16. QuartzCore

Cocoa Touch layer

1. UIKit
2. MessageUI
3. AddressBookUI
4. EventKitUI
5. GameKit
6. MapKit
7. Twitter
8. iAd

iOS Frameworks

1. Cocoa Touch layer
2. Media layer
3. Core services layer
4. Core OS layer