Objective-C

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Slides della sessione su Objective-C, tenuta da Giuseppe Arici all’iOS Bootcamp di pragmamark.

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Objective-C

  1. 1. Objective-C L’ABC del Linguaggio Giuseppe Arici § The Preacher
  2. 2. Giuseppe Arici Apple iOS & Mac OS X Addicted Developer Superpartes Innovation Campus & H-Farm Group Founder & Cocoa Preacher m # Pragma Mark ― pragmamark.org co pe y ;) ci. sep bo ari giu Fan A Social & Lazy Connected Node → ot a [ tt | in | fb | * ] / giuseppe.arici ard n Im Mail Forwarder & Spammer vC giuseppe.arici@gmail.com iOS Bootcamp
  3. 3. Alzi la mano chi ... ? iOS Bootcamp
  4. 4. Agenda ia & Fi losofia Stor tica & FisicaM atema iOS Bootcamp
  5. 5. The History iOS Bootcamp
  6. 6. 40 Years !1971 1981 1991 2001 2011 iOS Bootcamp
  7. 7. Dennis Ritchie @ Bell Labs1969 - 1973 iOS Bootcamp
  8. 8. Alan Kay @ Xerox PARC1972 - 1980 iOS Bootcamp
  9. 9. Steve Jobs & Steve Wozniak @  1976 iOS Bootcamp
  10. 10. Apple Team @ Xerox PARC 1979 iOS Bootcamp
  11. 11. Brad Cox & Tom Love @ ITT 1980 iOS Bootcamp
  12. 12. Byte Magazine # Agosto1981 1981 iOS Bootcamp
  13. 13. The “OOPC”1982 iOS Bootcamp
  14. 14. StepStone (formerly PPI) 1983 iOS Bootcamp
  15. 15. OOP An Evolutionary Approach 1986 iOS Bootcamp
  16. 16. Steve Jobs ⚡ John Sculley 1985 iOS Bootcamp
  17. 17. NeXT Computer (∡28°) 1986 iOS Bootcamp
  18. 18. NeXT ® Objective-C ⚐ StepStone 1988 iOS Bootcamp
  19. 19. WWW & Doom & Mathematica ☢NeXTcube 1991 iOS Bootcamp
  20. 20. NeXT + Sun = OpenStep API NSObject “Java Was Strongly Influenced by Objective-C” Patrick Naughton, co-creator of Java Programming Language 1993 iOS Bootcamp
  21. 21. NeXT ⊆ Apple 1996 iOS Bootcamp
  22. 22. Code Name “Rhapsody” 1997 iOS Bootcamp
  23. 23. Mac OS X v10.0 2001 iOS Bootcamp
  24. 24. clas fast se enu @p me xte rat rop ion nsio / fo r ert ns in y Objective-C 2.0 2006 gar opt bag ion ec new olle al pro c tion run @ tim toc OS e ol XiOS Bootcamp
  25. 25. The iPhone 2007 iOS Bootcamp
  26. 26. The iPhone SDK 2008 iOS Bootcamp
  27. 27. Chris Lattner @  Source: http://nondot.org/sabre/Resume.html Director and Architect, Low-Level Tools September 2011 - Ongoing Senior Manager and Architect, Low-Level Tools June 2010 - September 2011 Senior Manager of Compilers and Low-Level Tools, Compiler Architect September 2009 - June 2010 Manager of Compilers and Low-Level Tools, Compiler Architect July 2008 - September 2009 LLVM Compiler Group Manager and Compiler Architect December 2006 - July 2008 Senior Compiler Engineer and Tech Lead June 2005 - December 2006 2005 iOS Bootcamp
  28. 28. LLVM Compiler Infrastructure Source:The Architecture of Open Source Applications http://www.aosabook.org/en/llvm.html 2007 iOS Bootcamp
  29. 29. Clang (Static Analyzer) 2009 iOS Bootcamp
  30. 30. ^ Blocks & GCD 2009 iOS Bootcamp
  31. 31. Xcode 4 2010 iOS Bootcamp
  32. 32. Automatic Reference Counting * Messaggio Promozionale: http://www.whymca.org/intervento/automatic-reference-counting 2011 iOS Bootcamp
  33. 33. @s Enu ms ynt wit Ob hes hfi j ec ize xed t lit und by e rlyi era def aul ng typ ls t e WWDC 2012 Session 405: Modern Objective-C by Patrick C. Beard Modern Objective-C Un Sub ord Box scr ere ip dm ed ting eth Exp me od res dec 2012 tho l ara sio ds t ion n s siOS Bootcamp
  34. 34. TIOBE: Top 10 July 2012Source: http://www.tiobe.com/index.php/content/paperinfo/tpci/index.html iOS Bootcamp
  35. 35. TIOBE: Long Term Trends Source: http://www.tiobe.com/index.php/content/paperinfo/tpci/index.html iOS Bootcamp
  36. 36. TIOBE: Objective-C Programming Language of the Year 2011Source: http://www.tiobe.com/index.php/paperinfo/tpci/Objective-C.html iOS Bootcamp
  37. 37. Ipse dixit: Tom Love ⚔ C++ “Objective-C and C++ both started from C, but they went in two very different directions. Which approach do you prefer now? Tom: There’s the successful direction, and then there’s the approach that Bjarne took with C++. In one case, it was a small, simple — dare I say, elegant — programming language that was very crisp and well defined. In the other case it was a pretty ugly, complicated, difficult language that had some really troublesome features. I think those are the distinctions between the two.” iOS Bootcamp
  38. 38. Intervallo !? iOS Bootcamp
  39. 39. The Language iOS Bootcamp
  40. 40. Fundamental Laws iOS Bootcamp
  41. 41. A strict superset of C• Objective-C is not inspired by C language like Java or C#• Objective-C is a strict superset of the C language• Objective-C has only added some concepts and their associated keywords• Like with C++, a well-written C program should be compile-able as Objective-C• Unlike with C++, there is no risk of incompatibility between C names and Objective-C keywords iOS Bootcamp
  42. 42. A strict superset of C @@"" @( ) @[ ] @{ } @private@catch @property@class @protected@defs @protocol@dynamic @public@encode @required@end @selector@finally @synchronized@implementation @synthesize SEL BOOL@interface @throw IMP YES nil NO f de@optional @try pe Nil id ty in byref readwrite copy s er ts co i n out oneway readonly nonatomic ex et lar ble m nt inout getter assign strong self ra i cu i l a pa rt va bycopy setter retain weak super en pa a dd hi iOS Bootcamp
  43. 43. Requirements iOS Bootcamp
  44. 44. Objective-C void, char, int, long, float function pointer c {array} sizeof signed, unsigned c "string" function typedef, enum, union const, auto, static, extern # preprocessor (type)casting malloc, free C Standard Library for, do, whileif, else, switch, case int main(int argc, const char * argv[]) format specifiers %d %s stack vs heap *, &, [ ] member selection . -> Struct break, continue, goto iOS Bootcamp
  45. 45. Objective-C Polymorphism Message passing Subclass Method Class DelegationInstance Variable Superclass Method overriding Inheritance Dynamic dispatch / binding Encapsulation Abstraction Interface / Protocol iOS Bootcamp
  46. 46. Class iOS Bootcamp
  47. 47. Bad News NO namespaces ☹ Use prefix instead !NSObject, NSString, ...UIButton, UILabel, ...ABAddressBook, ABRecord, ...// Pragma MarkPMDeveloper, PMEvent, ... Draft Proposal for Namespaces in Objective-C: @namespace @using http://www.optshiftk.com/2012/04/draft-proposal-for-namespaces-in-objective-c/ iOS Bootcamp
  48. 48. Class #import @interface @implementation// Person.h // Person.m #import "Person.h"@interface Person : NSObject @implementation Person@end @end iOS Bootcamp
  49. 49. Class @interface#import <Foundation/Foundation.h>@interface BankAccount : NSObject{ NSInteger _balance;}- (NSInteger) withdraw:(NSInteger)amount;- (void) deposit:(NSInteger)amount;@end iOS Bootcamp
  50. 50. Class @interface#import <Foundation/Foundation.h>@interface BankAccount : NSObject{base types NSInteger _balance;} import- (NSInteger) withdraw:(NSInteger)amount;- (void) deposit:(NSInteger)amount;@end iOS Bootcamp
  51. 51. Class @interface#import <Foundation/Foundation.h>@interface BankAccount : NSObject{ NSInteger _balance;} class definition- start (NSInteger) withdraw:(NSInteger)amount;- (void) deposit:(NSInteger)amount;@end iOS Bootcamp
  52. 52. Class @interface#import <Foundation/Foundation.h>@interface BankAccount : NSObject{ NSInteger _balance;} class name- (NSInteger) withdraw:(NSInteger)amount;- (void) deposit:(NSInteger)amount;@end iOS Bootcamp
  53. 53. Class @interface extends#import <Foundation/Foundation.h>@interface BankAccount : NSObject{ NSInteger _balance;} parent class- (NSInteger) withdraw:(NSInteger)amount;- (void) deposit:(NSInteger)amount;@end iOS Bootcamp
  54. 54. Class @interface#import <Foundation/Foundation.h>@interface BankAccount : NSObject{ NSInteger _balance;} instance- (NSInteger) withdraw:(NSInteger)amount;- (void) deposit:(NSInteger)amount; variables@end iOS Bootcamp
  55. 55. Class @interface#import <Foundation/Foundation.h>@interface BankAccount : NSObject{ NSInteger _balance;}- (NSInteger) withdraw:(NSInteger)amount;- (void) deposit:(NSInteger)amount;@end methods declarations iOS Bootcamp
  56. 56. Class @interface#import <Foundation/Foundation.h>@interface BankAccount : NSObject{ NSInteger _balance;} class definition- (NSInteger) withdraw:(NSInteger)amount;- end (void) deposit:(NSInteger)amount;@end iOS Bootcamp
  57. 57. Class @implementation#import "BankAccount.h"@implementation BankAccount- (id) init { self = [super init]; return self;}- (NSInteger) withdraw:(NSInteger)amount { return amount;}- (void) deposit:(NSInteger)amount { _balance += amount;}@end iOS Bootcamp
  58. 58. Class @implementation#import "BankAccount.h"@implementation BankAccount interface- (id) init { import[super self = init]; return self;}- (NSInteger) withdraw:(NSInteger)amount { return amount;}- (void) deposit:(NSInteger)amount { _balance += amount;}@end iOS Bootcamp
  59. 59. Class @implementation#import "BankAccount.h"@implementation BankAccount- (id) init { class implementation self = [super init]; return self;} start- (NSInteger) withdraw:(NSInteger)amount { return amount;}- (void) deposit:(NSInteger)amount { _balance += amount;}@end iOS Bootcamp
  60. 60. Class @implementation#import "BankAccount.h"@implementation BankAccount- (id) init { self = [super init]; return self;}- (NSInteger) withdraw:(NSInteger)amount { return amount;} methods with- (void) deposit:(NSInteger)amount { _balance += amount; bodies}@end iOS Bootcamp
  61. 61. Class @implementation#import "BankAccount.h"@implementation BankAccount- (id) init { self = [super init]; return self;}- (NSInteger) withdraw:(NSInteger)amount { return amount;} class implementation- (void) deposit:(NSInteger)amount { end _balance += amount;}@end iOS Bootcamp
  62. 62. @class directive• @class directive provides minimal information about a class.• @class indicates that the name you are referencing is a class!• The use of the @class is known as a forward declaration// Rectangle.h // Rectangle.m#import "Shape.h" #import "Rectangle.h"@class Point; #import "Point.h"@interface Rectangle : Shape @implementation Rectangle- (Point *)center; - (Point *)center { // ... }@end @end iOS Bootcamp
  63. 63. Instance Variable Declaration@interface MyClass : NSObject{ @private // Can only be accessed by instances of MyClass NSInteger _privateIvar1; NSString *_privateIvar2; @protected // Default // Can only be accessed by instances of MyClass or MyClasss subclasses NSInteger _protectedIvar1; NSString *_protectedIvar2; @package // 64-bit only // Can be accessed by any object in the framework in which MyClass is defined NSInteger _packageIvar1; NSString *_packageIvar2;; @public // Never use it ! // Can be accessed by any object scope NSInteger _publicVar1; NSString *_publicVar2; qualifiers} iOS Bootcamp
  64. 64. Method & Message iOS Bootcamp
  65. 65. Method Declaration- (BOOL) writeToFile:(NSString *)path atomically:(BOOL)flag; In other languages, might be:bool MyClass::writeToFileAtomically(std::string path, bool flag); // C++public virtual bool WriteToFileAtomically(string path, bool flag); // C#public boolean writeToFileAtomically(String path, boolean flag); // Javapublic function writeToFileAtomically(path, flag) // PHPdef writeToFileAtomically(self, path, flag): # Pythondef writeToFileAtomically(path, flag) # Ruby iOS Bootcamp
  66. 66. Method Declaration - (BOOL) writeToFile:(NSString *)path atomically:(BOOL)flag; method scopeCan be either: + for a class method - for an instance methodMethods are always public ! “Private” methods defined in implementation iOS Bootcamp
  67. 67. Method Declaration - (BOOL) writeToFile:(NSString *)path atomically:(BOOL)flag; return typeCan be any valid data type, including: void returns nothing id a pointer to an object of any class NSString * a pointer to an NSString BOOL a boolean (YES or NO) iOS Bootcamp
  68. 68. Method Declaration - (BOOL) writeToFile:(NSString *)path atomically:(BOOL)flag; method nameThe method name is composed of all labelsColons precede arguments, but are part of the method name writeTofile:atomically: iOS Bootcamp
  69. 69. Method Declaration - (BOOL) writeToFile:(NSString *)path atomically:(BOOL)flag; argument type argument nameArguments come after or within the method nameVariadic methods can take variable arguments - (id)stringWithFormat:(NSString *)format ... stdarg: va_list va_start() va_arg() va_end() iOS Bootcamp
  70. 70. @selector SEL callback = @selector(writeToFile:atomically:); data type macro tofor selector create selectorConceptually similar to function pointerUseful for callback type behavior if ([helper respondsToSelector:callback]) { [helper performSelector:callback withObject:arguments]; } iOS Bootcamp
  71. 71. Message Passing• Methods are invoked by passing messages• Messages aren’t bound to method implementations until runtime. The compiler converts a message expression: [receiver message];• into a call on a messaging function objc_msgSend: objc_msgSend(receiver, selector);• Any arguments passed in the message are also handed to objc_msgSend: objc_msgSend(receiver, selector. arg1, arg2, ...); iOS Bootcamp
  72. 72. Message Passing[data writeToFile:@"/tmp/data.txt" atomically:YES]; In other languages, might be:data->writeToFileAtomically("/tmp/data.txt", true); // C++data.WriteToFileAtomically("/tmp/data.txt", true); // C#data.writeToFileAtomically("/tmp/data.txt", true); // Java$data->writeToFileAtomically("/tmp/data.txt", TRUE); // PHPdata.writeToFileAtomically(/tmp/data.txt, True) # Pythondata.writeToFileAtomically /tmp/data.txt, true # Ruby iOS Bootcamp
  73. 73. Message Passing [data writeToFile:@"/tmp/data.txt" atomically:YES]; square brackets syntaxNested Message Passing: [ [ ] [ ] [ [ ] ] ] [[store data] writeToFile:[@"/tmp/data.txt" lowercaseString] atomically:[[PMOption sharedOption] writeMode] encoding:NSUTF8StringEncoding error:&error]; iOS Bootcamp
  74. 74. Message Forwarding• In Objective C is very common to do message forwarding (a strategy pattern)• When an object receives a message and it does not have a corresponding method, it can delegates the task to another object- (void)forwardInvocation:(NSInvocation*)invocation { SEL sel = [invocation selector]; if ([helper respondsToSelector:sel]) { [invocation invokeWithTarget:helper]; } else { [self doesNotRecognizeSelector:sel]; }} iOS Bootcamp
  75. 75. Message Terminology• Message expression [data writeToFile:@"/tmp/data.txt" atomically:YES];• Message [data writeToFile:@"/tmp/data.txt" atomically:YES];• Selector [data writeToFile:@"/tmp/data.txt" atomically:YES];• Method { ... } // The code selected by a message iOS Bootcamp
  76. 76. Self & Super• Methods have implicit reference to owning object called self (similar to Java and C# this, but self is a l-value)• Additionally have access to superclass methods using super- (void)viewWillAppear:(BOOL)animated { [super viewWillAppear:animated]; [self reloadData];} iOS Bootcamp
  77. 77. ObjectLife Cycle iOS Bootcamp
  78. 78. Object Construction• NSObject defines class method called alloc • Dynamically allocates memory for object on the heap • Returns new instance of receiving class BankAccount *account = [BankAccount alloc];• NSObject defines instance method called init • Implemented by subclasses to initialize instance after memory has been allocated • Subclasses commonly define several initializers (default indicated in documentation) BankAccount *account = [[BankAccount alloc] init];• alloc and init calls are always nested into single line BankAccount *account = [[BankAccount alloc] init]; iOS Bootcamp
  79. 79. Object Construction initWith…• Needs to call super• Setup instance variables• Returns self - (id) init { self = [super init]; if (self) { _myInstanceVariable = @"Pragma Mark !"; } return self; } iOS Bootcamp
  80. 80. Object Destruction dealloc• Never call explicitly• Release all retained or copied instance variables (* if not ARC)• Calls [super dealloc] (* if not ARC) - (void)saveThis:(id)object { if (_myInstanceVariable != object ) { [_myInstanceVariable release]; _myInstanceVariable = [object retain]; } } - (void)dealloc { [_myInstanceVariable release]; [super dealloc]; } iOS Bootcamp
  81. 81. MemoryManagement iOS Bootcamp
  82. 82. Memory Management• Manual Reference Counting • Higher level abstraction than malloc / free • Straightforward approach, but must adhere to conventions and rules• Automatic Reference Counting (ARC) • Makes memory management the job of the compiler (and runtime) • Available for: partially iOS 4+ or OS X 10.6+ / fully iOS 5+ or OS X 10.7+• Garbage Collection • Only available for OS X 10.5+ • Not available on iOS due to performance concerns iOS Bootcamp
  83. 83. Manual Reference Counting(Only) objective-C objects are reference counted: • Objects start with retain count of 1 • Increased with retain • Decreased with release, autorelease • When count equals 0, runtime invokes dealloc 1 2 1 0 alloc retain release release dealloc iOS Bootcamp
  84. 84. Objects you create For objects you create with [[SomeClass alloc] init] or [myInstance copy] (without autoreleasing):• Retain should not need to be called• Release when you are done using it in the {code block}- (void)someMethod { NSArray *someArray = [[NSArray alloc] init]; _myInstanceVariable = someArray;}- (void)dealloc { [_myInstanceVariable release]; [super dealloc];} iOS Bootcamp
  85. 85. Objects you don’t create For objects you don’t create (e.g. get from methods):• Retain only when saving to instance (or static) variable• Release only if you retained it by saving it (as in above case)- (void)someMethod { id anObject = [someArray objectAtIndex:0]; _myInstanceVariable = [anObject retain];}- (void)dealloc { [_myInstanceVariable release]; [super dealloc];} iOS Bootcamp
  86. 86. AutoreleaseWhat if you create an object and you are returning it from amethod, how would you be able to release it?- (NSArray *)objects { NSArray *myArray = [[NSArray alloc] init]; ✇} return myArray; Leak ! ☠- (NSArray *)objects { NSArray *myArray = [[NSArray alloc] init]; return [myArray release];} Crash !- (NSArray *)objects { NSArray *myArray = [[NSArray alloc] init]; ☺ return [myArray autorelease];} Right ! iOS Bootcamp
  87. 87. Autorelease• Instead of explicitly releasing something, you mark it for a later release• An object called autorelease pool manages a set of objects to release when the pool is released• Add an object to the release pool by calling autorelease@autoreleasepool { // code goes here}NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];// code goes here[pool release]; iOS Bootcamp
  88. 88. Autorelease• Autorelease is NOT a Garbage Collector ! It is deterministic ⌚• Objects returned from methods are understood to be autoreleased if name is not in implicit retained set (alloc, new, init or copy)• If you spawn your own thread, you’ll have to create your own NSAutoreleasePool• Stack based: autorelease pools can be nested Friday Q&A 2011-09-02: Lets Build NSAutoreleasePool http://www.mikeash.com/pyblog/friday-qa-2011-09-02-lets-build-nsautoreleasepool.html iOS Bootcamp
  89. 89. Memory Management RuleEverything that increases the retain count withalloc, [mutable]copy[WithZone:] or retain is in charge of the corresponding [auto]release. From C++ to Objective-C http://pierre.chachatelier.fr/programmation/objective-c.php iOS Bootcamp
  90. 90. Automatic Reference Counting “Automatic Reference Counting (ARC) in Objective-C makes memory management the job of the compiler. By enabling ARC with the new Apple LLVM compiler, you will never need to type retain or release again, dramatically simplifying the development process, while reducing crashes and memory leaks. The compiler has a complete understanding of your objects, and releases each object the instant it is no longer used, so apps run as fast as ever, with predictable, smooth performance.” (Apple, “iOS 5 for developers” – http://developer.apple.com/technologies/ios5) iOS Bootcamp
  91. 91. Automatic Reference Counting• The Rule is still valid, but it is managed by the compiler• No more retain, release, autorelease nor dealloc• New lifetime qualifiers for objects, which includes zeroing weak references (only available on iOS 5+ & OS X 10.7+)• Apple provides a migration tool which is build into Xcode iOS Bootcamp
  92. 92. Automatic Reference Counting * Messaggio Auto-Promozionale: http://www.whymca.org/intervento/automatic-reference-counting iOS Bootcamp
  93. 93. Property iOS Bootcamp
  94. 94. Property• Objective-C 2.0 introduced new syntax for defining accessor code: • Much less verbose, less error prone • Highly configurable • Automatically generates accessor code• Complementary to existing conventions and technologies: • Key-Value Coding (KVC) • Key-Value Observing (KVO) • Cocoa Bindings • Core Data Simplifying Accessors iOS Bootcamp
  95. 95. Property Declaration@property(attributes) type name; Attribute Impacts readonly / readwrite Mutability setter / getter API nonatomic Concurrency assign / retain / copy weak / strong (* in ARC) Storage iOS Bootcamp
  96. 96. Property Declaration@property(attributes) type name; Attribute Impacts readonly / readwrite Mutability getter / setter API nonatomic Concurrency assign / retain / copy weak / strong (* in ARC) Storage@property(readonly) NSString *accountNumber; iOS Bootcamp
  97. 97. Property Declaration@property(attributes) type name; Attribute Impacts readonly / readwrite Mutability setter / getter API nonatomic Concurrency assign / retain / copy weak / strong (* in ARC) Storage@property(getter=isActive) BOOL active; iOS Bootcamp
  98. 98. Property Declaration@property(attributes) type name; Attribute Impacts readonly / readwrite Mutability getter / setter API nonatomic Concurrency assign / retain / copy weak / strong (* in ARC) Storage@property(nonatomic, retain) NSDate *createdAt; iOS Bootcamp
  99. 99. Property Declaration@property(attributes) type name; Attribute Impacts readonly / readwrite Mutability getter / setter API nonatomic Concurrency assign / retain / copy weak / strong (* in ARC) Storage@property(readwrite, copy) NSString *accountNumber; iOS Bootcamp
  100. 100. Retain CyclesParent Child retain1 1 retain iOS Bootcamp
  101. 101. Retain CyclesParent Child retain0 1 assign iOS Bootcamp
  102. 102. Retain Cycles assign X unsafe_unretainednil release X weak Controller ☺nil View as View Delegate New with ARC in iOS 5+ & OS X 10.7+ iOS Bootcamp
  103. 103. Property @interface#import <Foundation/Foundation.h>@interface BankAccount : NSObject { NSString *_accountNumber; NSDecimalNumber *_balance; NSDecimalNumber *_fees; BOOL _active;}@property(readwrite, copy) NSString *accountNumber;@property(readwrite, retain) NSDecimalNumber *balance;@property(readonly) NSDecimalNumber *fees;@property(getter=isActive) BOOL active;@end iOS Bootcamp
  104. 104. Property @interface#import <Foundation/Foundation.h>@interface BankAccount : NSObject { // No more instance variable declarations ! New in} iOS 4+ & OS X 10.6+@property(readwrite, copy) NSString *accountNumber;@property(readwrite, retain) NSDecimalNumber *balance;@property(readonly) NSDecimalNumber *fees;@property(getter=isActive) BOOL active;@end iOS Bootcamp
  105. 105. Property @implementation#import "BankAccount.h"@implementation BankAccount//...@synthesize accountNumber = _accountNumber;@synthesize balance = _balance;@synthesize fees = _fees;@synthesize active = _active;//...@end iOS Bootcamp
  106. 106. Property @implementation#import "BankAccount.h"@implementation BankAccount// No more @synthesize statements ! New in Xcode 4.4+ (WWDC 2012)//...@end iOS Bootcamp
  107. 107. Property Access• Generated properties are standard methods• Accessed through normal messaging syntax id value = [object property]; [object setProperty:newValue];• Objective-C 2.0 property access via dot syntax id value = object.property; object.property = newValue;• Dot notation is just syntactic sugar. Still uses accessor methods. Doesnt get/set values directly iOS Bootcamp
  108. 108. Protocol iOS Bootcamp
  109. 109. Protocol• List of method declarations • Not associated with a particular class • Conformance, not class, is important• Useful in defining • Methods that others are expected to implement • Declaring an interface while hiding its particular class • Capturing similarities among classes that arent hierarchically related Java / C# Interface done Objective-C style iOS Bootcamp
  110. 110. Protocol• Defining a Protocol@protocol NSCoding- (void)encodeWithCoder:(NSCoder *)aCoder;- (id)initWithCoder:(NSCoder *)aDecoder;@end• Adopting a Protocol@interface Person : NSObject<NSCoding> { NSString *_name;}// method & property declarations@end iOS Bootcamp
  111. 111. Protocol• Conforming to a Protocol@implementation Person// Partial implementation of conforming Person class- (id)initWithCoder:(NSCoder *)coder { if (self = [super init]) { _name = [coder decodeObjectForKey:@"name"]; [_name retain]; } return self;}- (void)encodeWithCoder:(NSCoder *)coder { [coder encodeObject:_name forKey:@"name"];}@end iOS Bootcamp
  112. 112. @required & @optional• Protocols methods are required by default• Can be relaxed with @optional directive@protocol SomeProtocol- (void)requiredMethod;@optional- (void)anOptionalMethod;- (void)anotherOptionalMethod;@required- (void)anotherRequiredMethod;@end iOS Bootcamp
  113. 113. Category & Extension iOS Bootcamp
  114. 114. Category• Add new methods to existing classes • Alternative to subclassing • Defines new methods and can override existing • Does not define new instance variables (* in case use Associative References) • Becomes part of the class definition (Inherited by subclasses)• Can be used as organizational tool• Often used in defining “private” methods Extending Object Features iOS Bootcamp
  115. 115. Category• Defining and using a Category// File NSString+PMAddition.h@interface NSString (PMAddition)- (NSString *)trim;@end// File NSString+PMAddition.m@implementation NSString (PMAddition)- (NSString *)trim { NSCharacterSet *cs; cs = [NSCharacterSet whitespaceAndNewlineCharacterSet]; return [self stringByTrimmingCharactersInSet:charSet];}@end#import "NSString+PMAddition.h"// ...NSString *string = @" A string to be trimmed";NSLog(@"Trimmed string: %@", [string trim]); iOS Bootcamp
  116. 116. Class Extension• Objective-C 2.0 adds ability to define anonymous categories • Class extension is unnamed • Treated as class interface continuations• Useful for implementing required “private” API• Compiler enforces methods are implemented Unnamed Categories iOS Bootcamp
  117. 117. Class Extension• Interface@interface Person : NSObject { NSUInteger _age;}- (NSUInteger)age;@end iOS Bootcamp
  118. 118. Class Extension• Implementation + “Private” Method@interface Person ()- (void)setAge:(NSUInteger)age;@end@implementation Person- (NSUInteger)age { return _age;}- (void)setAge:(NSUInteger)age { _age = age;}@end iOS Bootcamp
  119. 119. Exception & Block iOS Bootcamp
  120. 120. Exception • Very few uses for @try, @catch, @throw, and @finally • Reserve the use of exceptions for programming or unexpected runtime errors (very different from Java / C#) • NSError and the Cocoa error-delivery mechanism are the recommended way to communicate expected errors @try { // do something } @catch (NSException *e) { // handle exception } @finally { // close resources }- (BOOL)removeItemAtPath:(NSString *)path error:(NSError **)error; iOS Bootcamp
  121. 121. Block• Similar to standard C functions but, in addition to executable code, blocks may also contain variable bindings• Also called closures (or lambdas), because they close around variables in their scope New in• A nonstandard extension to C iOS 4+ & OS X 10.6+• Used as anonymous functionsint (^myBlock)(int) = ^(int num) { return num * multipier; };[objects sortUsingComparator:^(id firstObject, id secondObject) { return [firstObject compare:secondObject]; }]; iOS Bootcamp
  122. 122. Base Type iOS Bootcamp
  123. 123. Dynamic and Static Typing• Dynamically-typed object: id anObject; • Just id • Not id * (unless you really, really mean it: pointer to pointer)• Statically-typed object: BankAccount *anObject;• Objective-C provides compile-time type checking• Objective-C always uses dynamic binding iOS Bootcamp
  124. 124. The nil object pointer• Test for nil explicitly: if (nil == person) return; // Yoda Syntax <(-_-)>• Or implicitly: if (!person) return;• Can use in assignments and as arguments if expected person = nil; [button setTarget: nil];• Sending a message to nil? NO Problem ! person = nil; [person talk]; iOS Bootcamp
  125. 125. The BOOL typedef• When Objective-C was developed, C had no boolean type (C99 introduced one)• Objective-C uses a typedef to define BOOL as a type BOOL flag = NO;• Macro included for initialization and comparison: YES and NO if (flag) { // ... if (!flag) { // ... if (YES == flag) { // ... use !!flag if (NO == flag) { // ... flag = YES; flag = 1; iOS Bootcamp
  126. 126. Foundation Framework iOS Bootcamp
  127. 127. Framework• Frameworks are functionally similar to shared libraries• A compiled object that can be dynamically loaded into a programs address space at runtime• Frameworks add associated resources, header files, and documentation iOS Bootcamp
  128. 128. Foundation.framework• Values and Strings• Collections• User defaults• Archiving• Notifications• Tasks, timers, threads• File system, I/O, bundles• URL, XML, Scanner iOS Bootcamp
  129. 129. NSObject• Root Class @interface BankAccount : NSObject• Implements many basics • Memory management [anObject retain]; • Introspection if ([anObject isKindOfClass:[Person class]]) { • Object equality if ([obj1 isEqual:obj2]) { // NOT obj1 == obj2 • String representation (description is like toString() in Java or ToString() in C#) NSLog(@"%@", [anObject description]); NSLog(@"%@", anObject); // call description iOS Bootcamp
  130. 130. NSString @• General-purpose Unicode string support• NSString objects are conceptually UTF-16 endianness• Consistently used in Cocoa instead of “const char *”• Objective-C string literals start with @• NSString is immutable, NSMutableString is mutable const char *cString = "Pragma Mark"; // C string NSString *nsString = @"バンザイ"; // NSString @ cString = [nsString UTF8String]; nsString = [NSString stringWithCString:cString encoding:NSUTF8StringEncoding]; iOS Bootcamp
  131. 131. Format Strings• Similar to printf, but with %@ added for objects: NSString *title = @"The Preacher"; NSString *whoami = [NSString stringWithFormat: @"I am %@ !", title]; // whoami would be set to: // I am The Preacher !• Also used for logging with NSLog macro: NSLog(@"I am a %@, I have %d items", [array className], [array count]); // would log something like: // I am a NSArray, I have 42 items iOS Bootcamp
  132. 132. Collections• NSArray - ordered collection of objects• NSDictionary - collection of key-value pairs• NSSet - unordered collection of unique objects• Immutable and mutable versions • Immutable collections can be shared without side effect • Mutable objects typically carry a performance overhead NSDictionary *dic; dic = [[NSDictionary alloc] initWithObjectsAndKeys: @"ga", @"username", @"42", @"password", nil]; //nil to signify end of objects and keys. iOS Bootcamp
  133. 133. Collections• Collections can contain only objects• Wrap primitive types in NSNumber or NSValue• New literal syntax for: New in • array @[ obj, ... ] Xcode 4.4+ • dictionary @{ key : obj, ...} (WWDC 2012) • boxed expressions @( number or c string ) As a shortcut, number literals can be boxed without using the ( ) NSArray *a = @[@"42", @42, @"42", @3.14]; NSDictionary *d = @{ @1 : @"black", @2 : @"white"}; iOS Bootcamp
  134. 134. Fast Enumeration• Added in Objective-C 2.0• for in similar to Java / C# foreach• Use with NSArray, NSDictionary, NSSet or with any object of class that adopt the NSFastEnumeration protocol NSArray *people; // ... // Old school for (int i = 0; i < [people count]; ++i) { Person *person = [people objectAtIndex:i]; } // New school for (Person *person in people) { } iOS Bootcamp
  135. 135. Summary iOS Bootcamp
  136. 136. Objective-C• Fully C, Fully Object-Oriented, Powerful Dynamic Runtime• Objective-C 2.0 added many useful new features: • Garbage Collection for Mac OS X apps • Properties, Improved Categories & Protocols• Objective-C LLVM continues evolution: • Blocks (Closures) • Automatic Reference Counting • Synthesize by default for properties • New literals iOS Bootcamp
  137. 137. Objective-C Reference Books iOS Bootcamp
  138. 138. Are you bored !?The Objective-C Programming LanguageObjective-C Runtime Programming Guide iOS Bootcamp
  139. 139. Questions ? giuseppe.arici@gmail.comthepreacher@pragmamark.org iOS Bootcamp
  140. 140. What’s NeXT !? Objective-C ded Runtimes Delight Me Re y tap ent or loa rog em em Ob ra jec mm nag C: M tive ing -C inMa AR h al D k & atc isp ntr locCo de Ce t ^B W Gen ith er and ou LLV atio Gr All ab M n Never Say Never Again The Objective-C++ iOS Bootcamp
  141. 141. One More Thing ! iOS Bootcamp
  142. 142. Thanks ☺giuseppearici.com pragmamark.org iOS Bootcamp

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