NSObject
- 值类型:
    - NSAffineTransform
- NSCalendar
- NSCache
- NSValue
        - NSValue
- NSNumber
- NSDecimalNumber
 
- NSData
        - NSMutableData
- NSPurgeableData
 
- NSDate
- NSDateComponents
- NSDecimalNumberHandler
- NSLocale
- NSNull
- NSTimeZone
- NSValueTransformer
 
- XML
    - NSXMLParser
 
- Strings
    - NSAttributedString
- NSCharacterSet
- NSString
- NSFormatter
        - NSDateFormatter
- NSNumberFormatter
 
- NSScanner
- NSSortDescriptor
 
- Collections
    - NSArray
        - NSMutableArray
 
- NSDictionary
        - NSMutableDictionary
 
- NSNumerator
        - NSDirectoryEnumerator
 
- NSHashTable
- NSIndexPath
- NSIndexSet
        - NSMutableIndexSet
 
- NSMapTable
- NSPointerArray
- NSPointerFunctions
- NSSet
        - NSMutableSet
- NSCountedSet
 
 
- NSArray
        
- Predicates
    - NSExpression
- NSPredicate
        - NSComparisonPredicate
- NSCompoundPredicate
 
 
- Operating-System Services
    - NSError
- NSHost
- NSNetService
- NSNetServiceBrowser
- NSOrthography
- NSProcessInfo
- NSRunLoop
- NSSpeliServer
- NSTextCheckingResult
- NSTimer
- NSUserDefaults
 
- File System
    - NSBundle
- NSFileHandler
- NSFileManager
- NSMetadataItem
- NSMetadataQuery
- NSMetadataQueryAttributeValueTuple
- NSMetadataQueryResuleGroup
- NSStream
        - NSInputStream
- NSOutputStream
 
 
- URL
    - NSCachedURLResponse
- NSHTTPCookie
- NSHTTPCookieStorage
- NSURL
- NSURLAuthorizationChallenge
- NSURLCache
- NSURLSession
- NSURLCredential
- NSURLCredentialStorage
- NSURLDownload
- NSURLProtectionSpace
- NSURLProtocol
- NSURLRequest
        - NSMutableURLRequest
 
- NSURLResponse
        - NSHTTPURLResponse
 
 
- Interprocess Communication
    - NSPipe
- NSPort
        - NSMachPort
- NSMessagePort
- NSSockerPort
 
- NSPortMessage
- NSPortNameServer
        - NSMachBootstrapServer
- NSMessagePortNameServer
- NSSockerPortNameServer
 
 
- Locking-Threading
    - NSConditionLock
- NSDistributedLock
- NSLock
- NSOperation
        - NSBlockOperation
- NSInvocationOperation
 
- NSOperationQueue
- NSRecursiveLock
- NSTask
- NSThread
 
- Notifications
    - NSNotification
- NSNotificationCenter
        - NSNotificationQueue
 
 
- Archiving and Serialization
    - NSCoder
        - NSArchiver
- NSKeyedArchiver
- NSKeyedUnArchiver
- NSPortCoder
- NSUnarchiver
 
- NSPropertyListSerialization
 
- NSCoder
        
- Objective-C Language Service
    - NSSeertionHandler
- NSAutoreleasePool
- NSClassDescription
- NSException
- NSInvocation
- NSMethodSignature
- NSUndoManager
 
NSProxy
- [NSProxy1](https://blog.csdn.net/shubinniu/article/details/80895450)
- [消息转发](https://blog.csdn.net/liyanjun201/article/details/82620485)
- [NSProxy1](https://juejin.im/post/5afbca7bf265da0b8c25251d)
- NSProxy可以帮助Objective-C间接的实现多重继承的功能。
- OC 中一个类只有一个父类, 这就是单一继承, 但是我们可以用协议和 NSProxy 实现多继承