Giuseppe Arici § iOS Bootcamp @ ITIS

Objective-CThe Apple Programming Language

iOS Bootcamp @ ITIS

History

iOS Bootcamp @ ITIS

1976

Steve Jobs & Steve Wozniak @

iOS Bootcamp @ ITIS

1979

Apple Team @ Xerox PARC

iOS Bootcamp @ ITIS

1985

Steve Jobs ⚔ John Sculley

iOS Bootcamp @ ITIS

1986

NeXT Computer (∡28°)

iOS Bootcamp @ ITIS

1980

Brad Cox & Tom Love @ ITT

iOS Bootcamp @ ITIS

1986

OOP An Evolutionary Approach

iOS Bootcamp @ ITIS

1988

NeXT ® Objective-C ⚐ StepStone

iOS Bootcamp @ ITIS

1991

WWW & Doom & Mathematica

☢ NeXTcube

This machine is a server. DO NOT POWER DOWN !!

iOS Bootcamp @ ITIS

1996

NeXT ⊆ Apple

iOS Bootcamp @ ITIS

2001

Mac OS X v10.0

iOS Bootcamp @ ITIS

2007

The iPhone

iOS Bootcamp @ ITIS

2008

The iPhone SDK

iOS Bootcamp @ ITIS

Language

iOS Bootcamp @ ITIS

The Commandments

iOS Bootcamp @ ITIS

A strict superset of C

• Objective-C is a strict superset of the C language

• Objective-C is not inspired by C language like Java or C#

• 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 @ ITIS

A strict superset of C

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iOS Bootcamp @ ITIS

Requirements

iOS Bootcamp @ ITIS

*, &, [ ]

Objective-C

function

Struct

void, char, int, long, float

for, do, whileif, else, switch, case

typedef, enum, union

c "string"

const, auto, static, extern

member selection . ->

# preprocessor

c {array}

C Standard Library

sizeof

(type)casting

break, continue, goto

signed, unsigned

function pointer

malloc, free

format specifiers %d %s stack vs heap

int main(int argc, const char * argv[])

iOS Bootcamp @ ITIS

Inheritance

Objective-C

MethodClass

Polymorphism

Abstraction

Encapsulation

Message passing

Instance VariableDelegation

SuperclassMethod overriding

Subclass

Dynamic dispatch / binding

Interface / Protocol

iOS Bootcamp @ ITIS

Class

iOS Bootcamp @ ITIS

Class

@implementation

// Person.m

#import "Person.h"

@implementation Person

@end

#import

@interface

// Person.h

@interface Person : NSObject

@end

iOS Bootcamp @ ITIS

Class @interface

iOS Bootcamp @ ITIS

Class @interface

#import <Foundation/Foundation.h>

@interface BankAccount : NSObject{ NSInteger _balance;}

- (NSInteger) withdraw:(NSInteger)amount;- (void) deposit:(NSInteger)amount;

@end

iOS Bootcamp @ ITIS

Class @interface

#import <Foundation/Foundation.h>

@interface BankAccount : NSObject{ NSInteger _balance;}

- (NSInteger) withdraw:(NSInteger)amount;- (void) deposit:(NSInteger)amount;

@end

base types import

iOS Bootcamp @ ITIS

Class @interface

#import <Foundation/Foundation.h>

@interface BankAccount : NSObject{ NSInteger _balance;}

- (NSInteger) withdraw:(NSInteger)amount;- (void) deposit:(NSInteger)amount;

@end

class definition start

iOS Bootcamp @ ITIS

Class @interface

#import <Foundation/Foundation.h>

@interface BankAccount : NSObject{ NSInteger _balance;}

- (NSInteger) withdraw:(NSInteger)amount;- (void) deposit:(NSInteger)amount;

@end

class name

iOS Bootcamp @ ITIS

Class @interface

#import <Foundation/Foundation.h>

@interface BankAccount : NSObject{ NSInteger _balance;}

- (NSInteger) withdraw:(NSInteger)amount;- (void) deposit:(NSInteger)amount;

@end

parent class

extends

iOS Bootcamp @ ITIS

Class @interface

#import <Foundation/Foundation.h>

@interface BankAccount : NSObject{ NSInteger _balance;}

- (NSInteger) withdraw:(NSInteger)amount;- (void) deposit:(NSInteger)amount;

@end

instancevariables

iOS Bootcamp @ ITIS

Class @interface

#import <Foundation/Foundation.h>

@interface BankAccount : NSObject{ NSInteger _balance;}

- (NSInteger) withdraw:(NSInteger)amount;- (void) deposit:(NSInteger)amount;

@endmethods

declarations

iOS Bootcamp @ ITIS

Class @interface

#import <Foundation/Foundation.h>

@interface BankAccount : NSObject{ NSInteger _balance;}

- (NSInteger) withdraw:(NSInteger)amount;- (void) deposit:(NSInteger)amount;

@end

class definition end

iOS Bootcamp @ ITIS

Class @interface

#import <Foundation/Foundation.h>

@interface BankAccount : NSObject{ NSInteger _balance;}

- (NSInteger) withdraw:(NSInteger)amount;- (void) deposit:(NSInteger)amount;

@end

iOS Bootcamp @ ITIS

Class @implementation

iOS Bootcamp @ ITIS

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 @ ITIS

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

interfaceimport

iOS Bootcamp @ ITIS

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

class implementation start

iOS Bootcamp @ ITIS

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

methods with bodies

iOS Bootcamp @ ITIS

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

class implementation end

iOS Bootcamp @ ITIS

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 @ ITIS

Instance Variable Declaration

@interface MyClass : NSObject {

}

iOS Bootcamp @ ITIS

Instance Variable Declaration

@interface MyClass : NSObject { @private // Can only be accessed by instances of MyClass NSInteger _privateIvar1; NSString *_privateIvar2;

}

iOS Bootcamp @ ITIS

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 MyClass's subclasses NSInteger _protectedIvar1; NSString *_protectedIvar2;

}

iOS Bootcamp @ ITIS

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 MyClass's 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;

}

iOS Bootcamp @ ITIS

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 MyClass's 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 NSInteger _publicVar1; NSString *_publicVar2; }

iOS Bootcamp @ ITIS

@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.m#import "Rectangle.h"

#import "Point.h"

@implementation Rectangle

- (Point *)center { // ...}@end

// Rectangle.h#import "Shape.h"

@class Point;

@interface Rectangle : Shape

- (Point *)center;

@end

iOS Bootcamp @ ITIS

Bad News

NO namespaces :(Use prefix instead !

NSObject, NSString, ...

UIButton, UILabel, ...

ABAddressBook, ABRecord, ...

// Pragma MarkPMDeveloper, PMEvent, ...

Draft Proposal for Namespaces in Objective-C: @namespace @usinghttp://www.optshiftk.com/2012/04/draft-proposal-for-namespaces-in-objective-c/

iOS Bootcamp @ ITIS

Method & Message

iOS Bootcamp @ ITIS

Method Declaration

- (BOOL) writeToFile:(NSString *)path atomically:(BOOL)flag;

iOS Bootcamp @ ITIS

Method Declaration

- (BOOL) writeToFile:(NSString *)path atomically:(BOOL)flag;

method scope

Can be either:

+ for a class method

- for an instance method

Methods are always public !

“Private” methods defined in implementation

iOS Bootcamp @ ITIS

Method Declaration

- (BOOL) writeToFile:(NSString *)path atomically:(BOOL)flag;

return type

Can 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 @ ITIS

Method Declaration

- (BOOL) writeToFile:(NSString *)path atomically:(BOOL)flag;

method name

The method name is composed of all labels

Colons precede arguments, but are part of the method name

writeTofile:atomically:

iOS Bootcamp @ ITIS

Method Declaration

- (BOOL) writeToFile:(NSString *)path atomically:(BOOL)flag;

argument type

Arguments come after or within the method name

argument name

iOS Bootcamp @ ITIS

[data writeToFile:@"/tmp/data.txt" atomically:YES];

Message Passing

Nested Message Passing:

square brackets syntax

[[store data] writeToFile:[@"/tmp/data.txt" lowercaseString] atomically:[[PMOption sharedOption] writeMode] encoding:NSUTF8StringEncoding error:&error];

[ [ ] [ ] [ [ ] ] ]

iOS Bootcamp @ ITIS

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 @ ITIS

Object Life Cycle

iOS Bootcamp @ ITIS

Object Construction• NSObject defines class method called alloc

• Dynamically allocates memory for object on the heap

• Returns new instance of receiving class

• 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)

• alloc and init calls are always nested into single line

BankAccount *account = [BankAccount alloc];

BankAccount *account = [[BankAccount alloc] init];

[account init];

iOS Bootcamp @ ITIS

Object Destructiondealloc

• Never call explicitly

• Release all retained or copied instance variables (* if not ARC)

• Calls [super dealloc] (* if not ARC)

- (void)saveThis:(id)object { if (_instanceVariable != object ) { [_instanceVariable release]; _instanceVariable = [object retain]; } }

- (void)dealloc { [_instanceVariable release]; [super dealloc];}

iOS Bootcamp @ ITIS

Memory Management

iOS Bootcamp @ ITIS

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+, but depracated from 10.8+

• Not available on iOS due to performance concerns

iOS Bootcamp @ ITIS

Memory Management

Reference Count

iOS Bootcamp @ ITIS

Manual Reference Counting

retain

2

alloc

1

release

1

release

0

(Only) Objective-C objects are reference counted:

• Objects start with retain count of 1 when created

• Increased with retain

• Decreased with release, autorelease

• When count equals 0, runtime invokes dealloc

dealloc

iOS Bootcamp @ ITIS

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 @ ITIS

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: Let's Build NSAutoreleasePoolhttp://www.mikeash.com/pyblog/friday-qa-2011-09-02-lets-build-nsautoreleasepool.html

iOS Bootcamp @ ITIS

The Memory Management Rule

Everything that increases the reference count with alloc, copy, new or retain is in charge of

the corresponding [auto]release.

From C++ to Objective-Chttp://pierre.chachatelier.fr/programmation/objective-c.php

iOS Bootcamp @ ITIS

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 @ ITIS

Automatic Reference Counting

• The Rule is still valid, but it is managed by the compiler

• No more retain, [auto]release nor dealloc

• ARC is used in all new projects by default

• Apple provides a migration tool which is build into Xcode

iOS Bootcamp @ ITIS

Property

iOS Bootcamp @ ITIS

Property Access

• Generated properties are standard methods

• Accessed through normal messaging syntax

• Objective-C 2.0 property access via dot syntax

• Dot notation is just syntactic sugar. Still uses accessor methods. Doesn't get/set values directly

id value = [object property];[object setProperty:newValue];

id value = object.property;object.property = newValue;

iOS Bootcamp @ ITIS

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 @ ITIS

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 @ ITIS

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 @ ITIS

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 @ ITIS

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 @ ITIS

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 @ ITIS

Property @interface

#import <Foundation/Foundation.h>

@interface BankAccount : NSObject { NSString *_accountNumber; NSDecimalNumber *_balance; NSDecimalNumber *_fees; BOOL _active;}

@property(readwrite, copy) NSString *accountNumber;@property(readwrite, strong) NSDecimalNumber *balance;@property(readonly) NSDecimalNumber *fees;@property(getter=isActive) BOOL active;

@end

iOS Bootcamp @ ITIS

Property @interface

#import <Foundation/Foundation.h>

@interface BankAccount : NSObject { // No more instance variable declarations !

}

@property(readwrite, copy) NSString *accountNumber;@property(readwrite, strong) NSDecimalNumber *balance;@property(readonly) NSDecimalNumber *fees;@property(getter=isActive) BOOL active;

@end

New in iOS 4+ & OS X 10.6+

iOS Bootcamp @ ITIS

Property @implementation

#import "BankAccount.h"

@implementation BankAccount

//...

@synthesize accountNumber = _accountNumber;@synthesize balance = _balance;@synthesize fees = _fees;@synthesize active = _active;

//...

@end

iOS Bootcamp @ ITIS

Property @implementation

#import "BankAccount.h"

@implementation BankAccount

// No more @synthesize statements !

//...

@end

New in Xcode 4.4+

(WWDC 2012)

iOS Bootcamp @ ITIS

Protocol

iOS Bootcamp @ ITIS

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 aren't hierarchically related

Java / C# Interface done Objective-C style

iOS Bootcamp @ ITIS

Protocol

• Defining a Protocol

• Adopting a Protocol

@protocol NSCoding

- (void)encodeWithCoder:(NSCoder *)aCoder;- (id)initWithCoder:(NSCoder *)aDecoder;

@end

@interface Person : NSObject<NSCoding> { NSString *_name;}// method & property declarations@end

iOS Bootcamp @ ITIS

Base Types

iOS Bootcamp @ ITIS

Dynamic and Static Typing

• Dynamically-typed object:

• Just id

• Not id * (unless you really, really mean it: pointer to pointer)

• Statically-typed object:

• Objective-C provides compile-time type checking

id anObject;

BankAccount *anObject;

iOS Bootcamp @ ITIS

• Root Class

• Implements many basics

• Memory management

• Introspection

• Object equality

• String representation (description is like toString() in Java or ToString() in C#)

NSObject@interface BankAccount : NSObject

if ([anObject isKindOfClass:[Person class]]) {

if ([obj1 isEqual:obj2]) { // NOT obj1 == obj2

NSLog(@"%@", [anObject description]);NSLog(@"%@", anObject); // call description

[anObject retain];

iOS Bootcamp @ ITIS

• Objective-C string literals start with @

• Consistently used in Cocoa instead of “const char *”

• General-purpose Unicode string support

• NSString is immutable, NSMutableString is mutable

@”NSString”

const char *cString = "Pragma Mark"; // C stringNSString *nsString = @"バンザイ"; // NSString @

cString = [nsString UTF8String];nsString = [NSString stringWithCString:cString

encoding:NSUTF8StringEncoding];

iOS Bootcamp @ ITIS

• NSArray - ordered collection of objects

• NSDictionary - collection of key-value pairs

• NSSet - unordered collection of unique objects

• Immutable and mutable versions

Collections

NSDictionary *dic;dic = [[NSDictionary alloc] initWithObjectsAndKeys: @"ga", @"username", @"42", @"password", nil]; //nil to signify end of objects and keys.

iOS Bootcamp @ ITIS

Summary

iOS Bootcamp @ ITIS

• Objective-C is Fully C and Fully Object-Oriented

• Objective-C supports both strong and weak typing

• Objective-C is The Apple (only) Programming Language !

Objective-C

iOS Bootcamp @ ITIS

Questions

?

iOS Bootcamp @ ITIS

One More Thing !

iOS Bootcamp @ ITIS

NSLog(@”Thank you!”);

giuseppe.arici@pragmamark.org