Ios – Importing Foundation.h, but using :NSObject

iosobjective csuperclass

I am a bit confused what the ": SuperClass" is for. Let say I have a model class called MyClass, which is subclass of NSObject. I write in its interface that the class is subclass of NSObject, but actually I almost never import only NSObject header file. What I import is whole Foundation.h precompiled header file.

#import <Foundation/Foundation.h> 

@interface MyClass : NSObject

Is it only convention to write that I subclass from NSObject instead of Foundation, or is there any other meaning behind?

Best Answer

Foundation.h imports all the classes present in foundation framework and hence NSObject.h. If you just want to import NSObject.h the you should use

#import <Foundation/NSObject.h>

Below is the Foundation.h file source

/*  Foundation.h
    Copyright (c) 1994-2013, Apple Inc. All rights reserved.
*/


#include <CoreFoundation/CoreFoundation.h>

#import <Foundation/NSObjCRuntime.h>

#import <Foundation/NSArray.h>
#import <Foundation/NSAutoreleasePool.h>
#import <Foundation/NSBundle.h>
#import <Foundation/NSByteOrder.h>
#import <Foundation/NSCalendar.h>
#import <Foundation/NSCharacterSet.h>
#import <Foundation/NSCoder.h>
#import <Foundation/NSData.h>
#import <Foundation/NSDate.h>
#import <Foundation/NSDateFormatter.h>
#import <Foundation/NSDecimal.h>
#import <Foundation/NSDecimalNumber.h>
#import <Foundation/NSDictionary.h>
#import <Foundation/NSEnumerator.h>
#import <Foundation/NSError.h>
#import <Foundation/NSException.h>
#import <Foundation/NSFileHandle.h>
#import <Foundation/NSFileManager.h>
#import <Foundation/NSFormatter.h>
#import <Foundation/NSHashTable.h>
#import <Foundation/NSHTTPCookie.h>
#import <Foundation/NSHTTPCookieStorage.h>
#import <Foundation/NSIndexPath.h>
#import <Foundation/NSIndexSet.h>
#import <Foundation/NSInvocation.h>
#import <Foundation/NSJSONSerialization.h>
#import <Foundation/NSKeyValueCoding.h>
#import <Foundation/NSKeyValueObserving.h>
#import <Foundation/NSKeyedArchiver.h>
#import <Foundation/NSLocale.h>
#import <Foundation/NSLock.h>
#import <Foundation/NSMapTable.h>
#import <Foundation/NSMethodSignature.h>
#import <Foundation/NSNotification.h>
#import <Foundation/NSNotificationQueue.h>
#import <Foundation/NSNull.h>
#import <Foundation/NSNumberFormatter.h>
#import <Foundation/NSObject.h>
#import <Foundation/NSOperation.h>
#import <Foundation/NSOrderedSet.h>
#import <Foundation/NSOrthography.h>
#import <Foundation/NSPathUtilities.h>
#import <Foundation/NSPointerArray.h>
#import <Foundation/NSPointerFunctions.h>
#import <Foundation/NSPort.h>
#import <Foundation/NSProcessInfo.h>
#import <Foundation/NSPropertyList.h>
#import <Foundation/NSProxy.h>
#import <Foundation/NSRange.h>
#import <Foundation/NSRegularExpression.h>
#import <Foundation/NSRunLoop.h>
#import <Foundation/NSScanner.h>
#import <Foundation/NSSet.h>
#import <Foundation/NSSortDescriptor.h>
#import <Foundation/NSStream.h>
#import <Foundation/NSString.h>
#import <Foundation/NSTextCheckingResult.h>
#import <Foundation/NSThread.h>
#import <Foundation/NSTimeZone.h>
#import <Foundation/NSTimer.h>
#import <Foundation/NSURL.h>
#import <Foundation/NSURLAuthenticationChallenge.h>
#import <Foundation/NSURLCache.h>
#import <Foundation/NSURLConnection.h>
#import <Foundation/NSURLCredential.h>
#import <Foundation/NSURLCredentialStorage.h>
#import <Foundation/NSURLError.h>
#import <Foundation/NSURLProtectionSpace.h>
#import <Foundation/NSURLProtocol.h>
#import <Foundation/NSURLRequest.h>
#import <Foundation/NSURLResponse.h>
#import <Foundation/NSUserDefaults.h>
#import <Foundation/NSValue.h>
#import <Foundation/NSValueTransformer.h>
#import <Foundation/NSXMLParser.h>
#import <Foundation/NSZone.h>

#import <Foundation/FoundationErrors.h>

#if (TARGET_OS_MAC && !(TARGET_OS_EMBEDDED || TARGET_OS_IPHONE)) || (TARGET_OS_EMBEDDED || TARGET_OS_IPHONE)

#import <Foundation/NSAttributedString.h>
#import <Foundation/NSByteCountFormatter.h>
#import <Foundation/NSCache.h>
#import <Foundation/NSComparisonPredicate.h>
#import <Foundation/NSCompoundPredicate.h>
#import <Foundation/NSExpression.h>
#import <Foundation/NSFileCoordinator.h>
#import <Foundation/NSFilePresenter.h>
#import <Foundation/NSFileVersion.h>
#import <Foundation/NSFileWrapper.h>
#import <Foundation/NSLinguisticTagger.h>
#import <Foundation/NSMetadata.h>
#import <Foundation/NSMetadataAttributes.h>
#import <Foundation/NSNetServices.h>
#import <Foundation/NSPredicate.h>
#import <Foundation/NSProgress.h>
#import <Foundation/NSUbiquitousKeyValueStore.h>
#import <Foundation/NSUndoManager.h>
#import <Foundation/NSURLSession.h>
#import <Foundation/NSUUID.h>

#endif

#if (TARGET_OS_MAC && !(TARGET_OS_EMBEDDED || TARGET_OS_IPHONE)) || TARGET_OS_WIN32

#import <Foundation/NSArchiver.h>
#import <Foundation/NSCalendarDate.h>
#import <Foundation/NSConnection.h>
#import <Foundation/NSDistantObject.h>
#import <Foundation/NSDistributedNotificationCenter.h>
#import <Foundation/NSGeometry.h>
#import <Foundation/NSPortCoder.h>
#import <Foundation/NSPortMessage.h>
#import <Foundation/NSPortNameServer.h>
#import <Foundation/NSProtocolChecker.h>
#import <Foundation/NSTask.h>
#import <Foundation/NSXMLDTD.h>
#import <Foundation/NSXMLDTDNode.h>
#import <Foundation/NSXMLDocument.h>
#import <Foundation/NSXMLElement.h>
#import <Foundation/NSXMLNode.h>
#import <Foundation/NSXMLNodeOptions.h>
#import <Foundation/NSURLDownload.h>
#import <Foundation/NSURLHandle.h>

#endif

#if (TARGET_OS_MAC && !(TARGET_OS_EMBEDDED || TARGET_OS_IPHONE))

#import <Foundation/NSAffineTransform.h>
#import <Foundation/NSAppleEventDescriptor.h>
#import <Foundation/NSAppleEventManager.h>
#import <Foundation/NSAppleScript.h>
#import <Foundation/NSClassDescription.h>
#import <Foundation/NSDistributedLock.h>
#import <Foundation/NSGarbageCollector.h>
#import <Foundation/NSHFSFileTypes.h>
#import <Foundation/NSHost.h>
#import <Foundation/NSObjectScripting.h>
#import <Foundation/NSScriptClassDescription.h>
#import <Foundation/NSScriptCoercionHandler.h>
#import <Foundation/NSScriptCommand.h>
#import <Foundation/NSScriptCommandDescription.h>
#import <Foundation/NSScriptExecutionContext.h>
#import <Foundation/NSScriptKeyValueCoding.h>
#import <Foundation/NSScriptObjectSpecifiers.h>
#import <Foundation/NSScriptStandardSuiteCommands.h>
#import <Foundation/NSScriptSuiteRegistry.h>
#import <Foundation/NSScriptWhoseTests.h>
#import <Foundation/NSSpellServer.h>
#import <Foundation/NSUserNotification.h>
#import <Foundation/NSUserScriptTask.h>
#import <Foundation/NSXPCConnection.h>

#endif

About Is it only convention to write..

See you're not going to use only NSObject.h to implement your class, you may need NSArray/NSDictionary/NSDate/etc. etc. Thus instead of importing all these classes we usually import the Foundation.h

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