Exploring Objective-C: Language Overview & Development History

1. Toward iOS programming Objective-C

2. Overview • Objective-C is an object oriented language. • follows ANSI C style coding with methods from Smalltalk • Flexible almost everything is done at runtime. • Dynamic Binding • Dynamic Typing • Dynamic Linking

3. 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.

4. 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”

5. 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

6. 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

7. 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

8. The Cocoa API • 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

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

10. 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.h has been imported beforehand. #import “head.h”

11. Objective-C • Is a SUPERSET of C

12. Objective C--- some basics

13. Primitive data types from C • int, short, long • float,double • char

14. Operators same as C • + • - • * • / • ++ • --

15. Address and Pointers • Same as C • To get address of a variable i &i • Pointer int *addressofi = &I;

16. Logic and functions and main()….

17. Conditionals and Loops • Same as C/C++ • if / else if/ else • for • while • break • ontinue • do-while for(int i=0; i< 22; i++) { printf(“Checking i=“@d\n”, i); if(i+90 == i*i) { break;} }

18. for in loop • Introduced in Objective-C 2.0 (“fast enumeration”) for(Item_Type *item in Collection_of_Items) { //do whatever with the item Nslog(@” Looking now at %@”, item); } Note: %@ in the NSLogconverts whatever is passed (in this case item) to a string

19. Functions • Same as C/C++ • return_type functionName(type v1, type v2, ….) { //code of function } Example void showMeInfo(int age) { printf(“You are %d years old”, age); //or use NSLog() }

20. Global and static variables • Same as C/C++ • Global variables defined at top of file • For static variables use keyword static before it static in CurrentYear = 2013;

21. Functions --- pass by reference • Same as C/C++ return_type functionName(type v1, type *v2, ….) { //code of function } Example – call above int v1 = 2; int v2 = 3; functionName(v1, &v2);

22. Main Funciton –like C++ #import <whatever/what.h> int main(intargc, const char *argv[]) { @autoreleasepool { //your code here******* //you can have C code if you wish or Objective-C return 0; } } NOTE: Latest version of Objective-C uses AutomaticReference Counting (kind of like automatic garbage collection) ----to handle getting rid of not needed items in memory (avoidingmemory leaks). YEAH! AUTOMATIC! -----like Java this way @autoreleasepool in a needed annotation around your mainblock of code to “enable” this

23. IMPORTANT --- we are doing iOS applications NOT mac OS applications We will be doing iOS application that have a different framework called Model View Controller ---- But, for some examples to learn concepts of Objective-C we will show some basic main.m files with main functions that are not iOS programs!!! We will learn iOS soon!

24. Main Function –like C++ #import <whatever/what.h> int main(intargc, const char *argv[]) { @autoreleasepool { //takes care of “automatic release of not needed items //static method date with no parameters is invoked on NSDate class NSDate *now = [NSDate date]; //this will generate a new instance of NSDate with current time NSLog(@”The new date lives at %p”, now); //Objective-C function that is like printf to console double seconds = [now timeIntervalSince1970]//call timesInterrval* method on now object NSLog(@”It has been %f seconds since 1970”, seconds); NSDate *later = [now dateByAddingTimeInterval:100000];//pass 100000 parameter to method NSLog(@”In 100,000 seconds will be %@”, later); //%@ means print as string return 0; } }

25. Getting some output

26. Non-GUI – text output • Two standard functions you see used • printf() – same as C • printf(“Hi Lynne”); //this is actual C code • NSLog() • NSLog(@”Hi Lynne”); //this is strictly Objective-C

27. Objective C---okay into the weird stuff --- Classes and messages

28. Classes • Have both definition file and implementation file : classname.h and classname.m • Similar to how have .h and .cpp in C++

29. Declaring a class in ClassName.h #import <Cocoa/Cocoa.h> @interface ClassName : Parent { //class variables int age; NSString name; } // methods declared -(void)setAge:(int)number; -(void)setName:(NSString)n; -(int)getAge; -(NSString)getName; @end #import <standardimports.h> #import “local-your-otherfiles.h” @interface ClassName: Parent { //class variables } //methods -(return_type) methodName:(type)param1, (type) param2; @end

30. Declaring methods C++ syntax void function(int x, int y, char z); Object.function(x, y, z); Objective-C syntax -(void) method:(int)x, (int)y, (char)z; [Object function:x, y, z]; -(return type) function_name: (type) p1, (type) p2, ***; Apply function to Objectpassing parameters x,y,z

31. Whats this + and – stuff? • 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. (they are like static methods in Java invoked on class itself) • - indicates “instance methods” to be used by the client program (public functions) –invoked on an object / class instance . (they are like regular methods in Java invoked on object)

32. Class Implementation File (ClassName.m) #import “ClassName.h” @implementation ClassName -(void)setAge:(int)number { age = number; } -(void)setName:(NSString)n { name = n; } -(int)getAge { return age; } -(NSString)getName { return name; } @end Remember our ClassName.h #import <Cocoa/Cocoa.h> @interface ClassName : Parent { //class variables int age; NSString name; } // methods declared -(void)setAge:(int)number; -(void)setName:(NSString)n; -(int)getAge; -(NSString)getName; @end

33. An example….the class Node

34. 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 Class is Node who’s parent is NSObject { class variables } +/- private/public methods of Class Class variables are private

35. 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 Like your C++ .cpp file >>just give the methods here

36. How to create Objects

37. Creating class instances Creating an Object ClassName *object = [[ClassName alloc] init];  ClassName *object = [[ClassName alloc] initWith* ]; • NSString* myString = [[NSString alloc] init]; • Nested method call. The first is the alloc method called on NSString itself. This is a relatively low-level call which reserves memory and instantiates an object. The second is a call to init on the new object. The init implementation usually does basic setup, such as creating instance variables. The details of that are unknown to you as a client of the class. In some cases, you may use a different version of init which takes input: ClassName *object = [ClassName method_to_create]; • NSString* myString = [NSString string]; • Some classes may define a special method that will in essence call alloc followed by some kind of init

38. Object ---invoking a method, the basics • Objective-C uses a Message Approach

39. Messages ---really weird (new) syntax • 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. Like C++ or Java’s Identifier.message() [Identifier message ]

40. Setting values for class variables of an object ---- THROUGH methods [object methodName]; [object setXXXMethod:value1]; [object setYYYYMethod:value2];

41. C++ VS. Objective-C • 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

42. Keyword: id • 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… extern id Pen; id myPen; myPen = [Pen new ]; id work like pointers to objects.

43. Memory Allocation • Objects are created dynamically through the keyword, “alloc” • Objects are automatically deallocated in latest Objective-C through automatic reference counting

44. Automatic Reference Counting • Objective C uses ‘AUTOMATIC reference counting' as memory management • keeps an internal count of how many times an Object is 'needed'. • System makes sure that objects that are needed are not deleted, and when an object is not needed it is deleted.

45. iOS programs and @autoreleasepool • You will notice (later when you learn) your iOS applications are setup in Xcode (the IDE) with @autoreleasepool setup • This insures automatic release of unneeded items will take place for you.

46. Changing subjects –more on our Node class example ---lets create some child classes

47. linkList class linkList.m #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 Class linkList is child of previous Node class (not showing .h file for brevity)

48. Stack class (child of linkList) stack.h stack.m Remember alloc creates the object in memory #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]; //getValue method of parent linkList [self remove]; //remove method of parent linkList return ret; } @end self is like the C++/Java word this.

49. Example: main.m new is method defined in Stack class that simply that calls [Stack alloc] --- done for convinience #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; } release is method to release this object s explicitly from memory Run the program : 2 3 1 Note only need to import “stack.h” because stack imports LinkList.h which imports Node.h which imports cocoa.h

50. Objective-C data types