Cocoa Programming. David Chisnall. March 18,

Transcription

1 March 18,

2 The Story So Far What is Cocoa? Why Cocoa? GNUstep Overview GNUstep Look and Feel

3 A Brief History of Objective-C 1980: Smalltalk-80 needed a really powerful workstation (512KB of RAM and a 5.8MHz CPU? Who can afford that?!) 1983: Object-Oriented Pre-Compiler adds Smalltalk-like objects to C. 1986: Objective-C adds Smalltalk-like syntax too. 1988: NeXT licenses Objective-C StepStone, rewrtes Objective-C compiler. 2002: Apple 2007: Apple introduces Objective-C 2, the version that comes after Objective-C 4.0. Apparently this makes sense.

4 From OpenStep to Cocoa 1985: Steve Jobs leaves Apple to create the perfect workstation. 1988: NeXT Computer ships with first commercial Rapid Application Development environment. 1990: Tim Berners-Lee writes WorldWideWeb, credits NeXT developer tools for making it possible. 1991: Sun joins NeXT to make a set of portable APIs. 1994: OpenStep specification published, GNUstep project starts implementing it. 1997: Apple buys NeXT, renames their OpenStep implementation Yellow Box. 2001: OS X 10.0 released, Yellow Box renamed Cocoa. GNUstep begins tracking Cocoa.

5 What is Cocoa? The Story So Far What is Cocoa? Why Cocoa? Applications Core Data Address Book AppKit Foundation CoreAnimation CoreGraphics WindowServer libobjc Core Foundation libc XNU

6 What is Cocoa? The Story So Far What is Cocoa? Why Cocoa? Applications Core Data Address Book AppKit Foundation CoreAnimation CoreGraphics WindowServer libobjc Core Foundation libc XNU

7 What is Cocoa? Why Cocoa? What Makes Cocoa Special? Loose coupling everywhere (dynamic dispatch, notifications, KVC/KVO, and so on) Generic solutions (NSController, and so on) No magic (but lots of sufficiently advanced technology )

8 Dictionaries as Factories 1 - ( void ) registerhandlerclass : ( Class ) aclass 2 fortag : ( NSString *) atag 3 { 4 [ handlers setobject : aclass forkey : atag ]; 5 } 6 - ( void ) opentag : ( NSString *) tag 7 attributes : ( NSDictionary *) attrs 8 { 9 [ self pushdelegate : 10 [[[ handlers objectforkey : tag ] new ] autorelease ]]; 11 [ delegate opentag : tag attributes : attrs ]; 12 }

9 Dictionaries as Switch Statements 1 - ( void ) registerhandler : ( SEL ) asel 2 forexception : ( NSString *) except 3 { 4 NSValue * boxedsel = 5 [ NSValue valuewithbytes : & asel 6 objctype ( SEL )]; 7 [ handlers setobject : boxedsel forkey : except ]; 8 /* Or: 9 [ handlers setobject : NSStringFromSelector ( sel ) 10 forkey : except ]; 11 */ 12 }

10 Dictionaries as Switch Statements ( NSException *e) 2 { 3 SEL sel selector ( ignore :); 4 NSValue * boxedsel = 5 [ handlers objectforkey : [ e name ]]; 6 [ boxedsel getvalue : & sel ]; 7 [ self performselector : sel withobject : e]; 8 // Or: 9 // objc_msgsend (self, sel, e); 10 }

11 Why Dictionaries? Objective-C message sending depends on two things: the class and selector. Classes are objects. Selectors can be treated as objects.

12 What is? Based on the idea of higher-order functions. Messages that (appear to) take messages as arguments. Implemented with proxies. Some overhead, but make code much smaller.

13 HOM Examples 1 NSArray * uppercase = 2 [[ array map ] uppercasestring ]; 3 [[ delegate ifresponds ] handlearray : uppercase ]; 4 [[ mediaplayer innewthread ] playfile : afile ]; All of these work with EtoileFoundation (on OS X and GNUstep).

14 Implementing -ifresponds implementation IfRespondsProxy 2 // methodsignatureforselector omitted 3 - ( void ) forwardinvocation : ( NSInvocation *) aninvocation 4 { 5 if ([ object respondstoselector : [ aninvocation selector ]]) 6 [ aninvocation invokewithtarget : object ]; 7 } implementation NSObject ( IfResponds ) 10 - (id) ifresponds 11 { 12 return [ IfRespondsProxy proxyforobject : self ]; 13 }

15 Things to Remember -forwardingtargetforselector: can make proxies much faster. -methodsignatureforselector must return something. This can be complicated. HOM code is relatively slow, but very concise.

16 Creating 1 // Cache these values 2 Class class = [ NSMutableIndexSet class ]; 3 size_t size = class_getinstancesize ( class ); 4 struct { Class isa ; 5 char obj [size - sizeof ( Class )]; } obj ; 6 memset (& obj, 0, size ); 7 obj. isa = class ; 8 NSMutableIndexSet * set = 9 ( NSMutableIndexSet *)& obj ; 10 [ set init ]; 11 [ set addindex : 1]; 12 // This will crash! 13 // [ set dealloc ];

17 Important Notes Don t do this. Ever. Really. The performance gain is tiny for most objects. The code is really fragile. (Experts only) Design classes explicitly for stack allocation if you must do it.

18 State Machines Handle input. Process it depending on the current state. Useful for network protocols, and so on.

19 Implementing State Machines 1 - ( void ) handleinput : ( char )a 2 { 3 switch ( state ) 4 { case STATE_ A : 7 // Do something with the input 8 state = STATE_ B ; 9 return ; State variable in class tracks state. Switch statements everywhere. Simple model, unmaintainable code.

20 isa-swizzling Objective-C objects have a pointer to their class. The first instance variable, isa, holds this pointer. You can change this at run time.

21 State Machines with isa-swizzling 1 - ( void ) handleinput : ( char )a 2 { 3 // Handle the input 4 isa = [ NewState class ]; 5 } One subclass per state. One method per action. Simpler code.

22 Caveats Using isa-swizzling breaks KVO (and potentially other things). Class layouts must be the same!

23 GNUstep Overview GNUstep Look and Feel GNUstep tracks Cocoa changes. Request driven - classes and methods that people need get implemented first. Foundation will implement all of 10.4 in next release. AppKit will implement all of 10.2 in next release. Some bits of 10.6 are already working in both.

24 What is GNUstep? The Story So Far GNUstep Overview GNUstep Look and Feel Applications Core Data Address Book AppKit Foundation Cairo -back libobjc X.org / GDI libc Linux / FreeBSD / WinNT /

25 Is that all? The Story So Far GNUstep Overview GNUstep Look and Feel Applications Core Data Address Book AppKit Foundation Cairo -back libobjc X.org / GDI libc Linux / FreeBSD / WinNT /

26 GNUstep Overview GNUstep Look and Feel

27 The Story So Far GNUstep Overview GNUstep Look and Feel Bean requires OS X 10.4 or newer.

28 Objective-C 2 Features The Story So Far GNUstep Overview GNUstep Look and Feel clang clang libobjc2 Feature GCC ObjectiveC2 libobjc2 nonfragile Zero-cost EH OS X 10.5 runtime APIs Properties Fast Enumeration Protocol introspection Fast Proxies Non-fragile ivars Object planes Garbage Collection WIP Clang + libobjc2 has feature parity with iphone runtime