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Objective-C

Objective-C. First Part adapted from a presentation by Kevin Layer. Main Points. A Bit of History Main Features Some Examples. Overview. Objective-C is an object oriented language. follows ANSI C style coding with methods from Smalltalk There is no formal written standard

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Objective-C

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  1. Objective-C First Part adapted from a presentation by Kevin Layer

  2. Main Points A Bit of History Main Features Some Examples

  3. Overview • Objective-C is an object oriented language. • follows ANSI C style coding with methods from Smalltalk • There is no formal written standard • Relies mostly on libraries written by others • Flexible almost everything is done at runtime. • Dynamic Binding • Dynamic Typing • Dynamic Linking

  4. Inventors • Objective-C was invented by two men, Brad Cox and Tom Love. • Both were introduced to Smalltalk at ITT in 1981 • Cox thought something like Smalltalk would be very useful to application developers • Cox modified a C compiler and by 1983 he had a working Object-oriented extension to C called OOPC.

  5. Development • Tom Love acquired a commercial copy of Smalltalk-80 while working for Schlumberger Research • With direct access Smalltalk, Love added more to OOPC making the final product, Objective-C. • In 1986 they release Objective-C through their company “Stepstone”

  6. NeXT and NeXTSTEP • In 1988 Steve Jobs acquires Objective-C license for NeXT • Used Objective-C to build the NeXTSTEP Operating System • Objective-C made interface design for NeXTSTEP much easier • NeXTSTEP was derived from BSD Unix • In 1995 NeXT gets full rights to Objective-C from Stepstone

  7. OPENSTEP API • Developed in 1993 by NeXT and Sun • An effort to make NeXTSTEP-like Objective-C implementation available to other platforms. • In order to be OS independent • Removed dependency on Mach Kernel • Made low-level data into classes • Paved the way for Mac OS X, GNUstep

  8. Apple and Mac OS X • NeXT is taken over by Apple in 1996 and put Steve Jobs and his Objective-C libraries to work • Redesigned Mac OS to use objective-C similar to that of NeXTSTEP • Developed a collection of libraries named “Cocoa” to aid GUI development • Release Mac OS X (ten), which was radically different than OS 9, in March 2001

  9. The Cocoa API • Primarily the most frequently used frameworks nowadays. • Developed by Apple from NeXTSTEP and OPENSTEP • Has a set of predefined classes and types such as NSnumber, NSstring, Nsdate, etc. • NS stands for NeXT-sun • Includes a root class NSObject where words like alloc, retain, and release come from

  10. Dynamic Language • Almost everything is done at runtime • Uses dynamic typing, linking, and binding • This allows for greater flexibility • Minimizes RAM and CPU usage

  11. To Import or Include? • C/C++’s #include will insert head.h into the code even if its been added before. • Obj-C’s #import checks if head.hhas been imported beforehand. #import head.h

  12. Messages • Almost every object manipulation is done by sending objects a message • Two words within a set of brackets, the object identifier and the message to send. • Because of dynamic binding, the message and receiver are joined at runtime [Identifier message ]

  13. Basic syntax structure C++ syntax void function(int x, int y, char z); Object.function(x, y, z); Objective-C syntax -(void) function:(int)x, (int)y, (char)z; [Object function:x, y, z];

  14. The word ‘id’ indicates an identifier for an object much like a pointer in c++ This uses dynamic typing For example, if Pen is a class… Keyword: id id myPen; myPen = [Pen new ];

  15. Memory Allocation • Objects are created dynamically through the keyword, “alloc” • Objects are dynamically deallocated using the words “release” and “autorelease” • autorelease dealocates the object once it goes out of scope. • NOTE: None of these words are built-in

  16. Ownership • Objects are initially owned by the id that created them. • Like C++ pointers, multiple IDs can use the same object. • However, like in C++ if one ID releases the object, then any remaining pointers will be referencing invalid memory. • A method like “retain” can allow the object to stay if one ID releases it.

  17. Prototyping functions • When declaring or implementing functions for a class, they must begin with a + or - • + indicates a “class method” that can only be used by the class itself. In other words, they’re for private functions. • - indicates “instance methods” to be used by the client program (public functions).

  18. Class Declaration (Interface) #import <Cocoa/Cocoa.h> @interface Node : NSObject { Node *link; int contents; } +(id)new; -(void)setContent:(int)number; -(void)setLink:(Node*)next; -(int)getContent; -(Node*)getLink; @end node.h

  19. Class Definition (Implementation) #import "node.h” @implementation Node +(id)new { return [Node alloc];} -(void)setContent:(int)number {contents = number;} -(void)setLink:(Node*)next { [link autorelease]; link = [next retain]; } -(int)getContent {return contents;} -(Node*)getLink {return link;} @end node.m

  20. Adds OOP, metaprogramming and generic programming to C Comes with a std library Has numerous uses Large and complex code for OOP Only adds OOP to C Has no standard library; is dependant on other libraries Mostly used for application building Simpler way of handling classes and objects C++ VS. Objective-C

  21. Objective-C 2.0 • In October 2007, Apple Inc. releases Objective-C 2.0 for Mac OS 10.5 (Leopard) • Adds automatic garbage collection • Instance Methods (public functions) are defined differently using @property

  22. #import "linkList.h" @implementation linkList +(id)new {return [linkList alloc];} -(void)insert:(int)value { id temp = [Node new]; [temp setContent:value]; [temp setLink:head]; head = [temp retain]; [temp release]; } -(void)append:(int)value { id last = [head getLink]; while ([last getLink] != nil) {last = [last getLink];} id temp = [Node new]; [temp setContent:value]; [last setLink:temp]; [temp release]; } -(void)remove { id temp = head; head = [head getLink]; [temp release]; } -(int)getValue { return [head getContent];} @end linkList class linkList.m

  23. #import "linkList.h” @interface Stack : linkList {} +(id)new; -(void)push:(int)value; -(int)pop; @end #import "stack.h” @implementation Stack +(id)new {return [Stack alloc];} -(void)push:(int)value {[self insert:value];} -(int)pop { int ret = [self getValue]; [self remove]; return ret; } @end Stack class stack.h stack.m

  24. #import "stack.h” int main(){ Stack *s = [Stack new]; [s push:1]; [s push:2]; printf("%d\t", [s pop]); [s push:3]; printf("%d\t", [s pop]); printf("%d\t", [s pop]); [s release]; return 0; } Example: main.c main.c

  25. Example 1 #import <Foundation/Foundation> int main (intargc, const char * argv[]) { NSString *testString; testString = [[NSStringalloc] init]; testString = @"Here's a test string in testString!"; NSLog(@"testString: %@", testString); return 0; }

  26. The Interface @interface SimpleCar : NSObject { NSString* make; NSString* model; NSNumber* vin; } // set methods - (void) setVin: (NSNumber*) newVin; - (void) setMake: (NSString*) newMake; - (void) setModel: (NSString*) setModel; - (void) setMake: (NSString*) newMake Model: (NSString*) newModel; // get methods - (NSString*) make; - (NSString*) model; - (NSNumber*) vin; @end

  27. Implementation @implementation SimpleCar // set methods - (void) setVin: (NSNumber*) newVin{ [vin release]; vin = [[NSNumberalloc] init]; vin = newVin; } - (void) setMake: (NSString*) newMake{ [make release]; make = [[NSStringalloc] initWithString:newMake]; } - (void) setModel: (NSString*) newModel{ [model release]; model = [[NSStringalloc] initWithString:newModel]; }

  28. Implementation Continued - (void) setMake: (NSString*) newMake Model: (NSString*) newModel{ // Reuse our methods from earlier [self setMake:newMake]; [self setModel:newModel];

  29. Implementation continued … // get methods - (NSString*) make { return make; } - (NSString*) model { return model; } - (NSNumber*) vin { return vin; } @end

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