Objective-C @ ITIS

Giuseppe Arici § iOS Bootcamp @ ITIS

Objective-CThe Apple Programming Language

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History

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1976

Steve Jobs & Steve Wozniak @

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1979

Apple Team @ Xerox PARC

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1985

Steve Jobs ⚔ John Sculley

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1986

NeXT Computer (∡28°)

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1980

Brad Cox & Tom Love @ ITT

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1986

OOP An Evolutionary Approach

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1988

NeXT ® Objective-C ⚐ StepStone

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1991

WWW & Doom & Mathematica

☢ NeXTcube

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

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1996

NeXT ⊆ Apple

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2001

Mac OS X v10.0

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2007

The iPhone

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2008

The iPhone SDK

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Language

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The Commandments

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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

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A strict superset of C

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Requirements

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*, &, [ ]

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[])

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Inheritance

Objective-C

MethodClass

Polymorphism

Abstraction

Encapsulation

Message passing

Instance VariableDelegation

SuperclassMethod overriding

Subclass

Dynamic dispatch / binding

Interface / Protocol

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Class

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Class

@implementation

// Person.m

#import "Person.h"

@implementation Person

@end

#import

@interface

// Person.h

@interface Person : NSObject

@end

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Class @interface

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Class @interface

#import <Foundation/Foundation.h>

@interface BankAccount : NSObject{ NSInteger _balance;}

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

@end

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Class @interface




@end

base types import

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Class @interface




@end

class definition start

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Class @interface




@end

class name

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Class @interface




@end

parent class

extends

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Class @interface




@end

instancevariables

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Class @interface




@endmethods

declarations

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Class @interface




@end

class definition end

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Class @interface




@end

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Class @implementation

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#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

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interfaceimport

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class implementation start

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methods with bodies

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class implementation end

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Instance Variable Declaration

@interface MyClass : NSObject {

}

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

}

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@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;

}

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@package // 64-bit only // Can be accessed by any object in the framework in which MyClass is defined NSInteger _packageIvar1; NSString *_packageIvar2;

}

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@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; }

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@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

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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/

http://www.optshiftk.com/2012/04/draft-proposal-for-namespaces-in-objective-c/

http://www.optshiftk.com/2012/04/draft-proposal-for-namespaces-in-objective-c/

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Method & Message

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Method Declaration

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

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Method Declaration


method scope

Can be either:

+ for a class method

- for an instance method

Methods are always public !

“Private” methods defined in implementation

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Method Declaration


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)

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Method Declaration


method name

The method name is composed of all labels

Colons precede arguments, but are part of the method name

writeTofile:atomically:

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Method Declaration


argument type

Arguments come after or within the method name

argument name

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[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];

[ [ ] [ ] [ [ ] ] ]

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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];}

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Object Life Cycle

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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];

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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];}

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Memory Management

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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

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Memory Management

Reference Count

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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

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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];

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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

http://www.mikeash.com/pyblog/friday-qa-2011-09-02-lets-build-nsautoreleasepool.html

http://www.mikeash.com/pyblog/friday-qa-2011-09-02-lets-build-nsautoreleasepool.html

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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

https://encrypted.google.com/url?sa=t&rct=j&q=from%20objective%20c%20c%2B%2B&source=web&cd=2&ved=0CFwQFjAB&url=http%3A%2F%2Fpierre.chachatelier.fr%2Fprogrammation%2Ffichiers%2Fcpp-objc-en.pdf&ei=k3X0T5XmGsei-gax3ZHaBg&usg=AFQjCNEhpLjpUUJ5e_vWoj9VdMShNotFRQ&cad=rja

https://encrypted.google.com/url?sa=t&rct=j&q=from%20objective%20c%20c%2B%2B&source=web&cd=2&ved=0CFwQFjAB&url=http%3A%2F%2Fpierre.chachatelier.fr%2Fprogrammation%2Ffichiers%2Fcpp-objc-en.pdf&ei=k3X0T5XmGsei-gax3ZHaBg&usg=AFQjCNEhpLjpUUJ5e_vWoj9VdMShNotFRQ&cad=rja

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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)

http://developer.apple.com/technologies/ios5

http://developer.apple.com/technologies/ios5

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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

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Property

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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;

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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

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Property Declaration@property(attributes) type name;

Attribute Impacts

readonly / readwrite Mutability

setter / getter API

nonatomic Concurrency

assign / retain / copy weak / strong (* in ARC) Storage

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Attribute Impacts


getter / setter API



@property(readonly) NSString *accountNumber;

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Attribute Impacts


setter / getter API



@property(getter=isActive) BOOL active;

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Attribute Impacts


getter / setter API



@property(nonatomic, retain) NSDate *createdAt;

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Attribute Impacts


getter / setter API



@property(readwrite, copy) NSString *accountNumber;

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Property @interface


@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

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Property @interface


@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+

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Property @implementation



//...

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

//...

@end

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Property @implementation



// No more @synthesize statements !

//...

@end

New in Xcode 4.4+

(WWDC 2012)

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Protocol

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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

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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

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Base Types

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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;

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• 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];

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• 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];

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• 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.

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Summary

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• 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

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Questions

?

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One More Thing !

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NSLog(@”Thank you!”);

[email protected]

mailto:[email protected]?subject=%5BiOS%20Bootcamp%20@%20ITIS%5D%20

mailto:[email protected]?subject=%5BiOS%20Bootcamp%20@%20ITIS%5D%20

Objective-C @ ITIS

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