Objective-C - IEEE UNIPV Student Branchieee.unipv.it/documents/Objective_C.pdf• Objective-C 2.0...

Giuseppe Arici § iOS Bootcamp

Objective-CThe Apple Programming Language

iOS Bootcamp

History

iOS Bootcamp

Once upon a time …

Bells / Xerox / Apple / Xerox / ITT / StepStone / NeXT / Cern / Sun / Apple

1979

1976

1972

1970

1988

1985

1984

1980

1997

1996

1993

1991

2008

2007

2005

2001

iOS Bootcamp

Language

iOS Bootcamp

A strict superset of C

@@"" @( ) @[ ] @{ } @catch @class @defs @dynamic @encode @end @finally @implementation @interface @optional

@private @property @protected @protocol @public @required @selector @synchronized @synthesize @throw @try

SEL IMP nil Nil

BOOL YES NO id typ

edef

self super

hidde

n par

amete

rsin out inout bycopy

byref oneway getter setter

readwrite readonly assign retain

copy nonatomic strong weak av

ailab

le in

parti

cular

cont

exts

iOS Bootcamp

*, &, [ ]

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

Inheritance

Objective-C

MethodClass

Polymorphism

Abstraction

Encapsulation

Message passing

Instance VariableDelegation

SuperclassMethod overriding

Subclass

Dynamic dispatch / binding

Interface / Protocol

iOS Bootcamp

Class

iOS Bootcamp

Class

@implementation

// Person.m !#import "Person.h" !@implementation Person !@end

#import

@interface

// Person.h !!!@interface Person : NSObject !@end

iOS Bootcamp

Class @interface

iOS Bootcamp

Class @interface

#import <Foundation/Foundation.h> !@interface BankAccount : NSObject { NSInteger _balance; } !- (NSInteger) withdraw:(NSInteger)amount; - (void) deposit:(NSInteger)amount; !@end

iOS Bootcamp

Class @interface


base types import

iOS Bootcamp

Class @interface


class definition start

iOS Bootcamp

Class @interface


class name

iOS Bootcamp

Class @interface


parent class

extends

iOS Bootcamp

Class @interface


instance variables

iOS Bootcamp

Class @interface


methods declarations

iOS Bootcamp

Class @interface


class definition end

iOS Bootcamp

Class @interface


iOS Bootcamp

Class @implementation

!!

iOS Bootcamp


#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



interface import

iOS Bootcamp



class implementation start

iOS Bootcamp



methods with bodies

iOS Bootcamp



class implementation end

iOS Bootcamp



iOS Bootcamp

Instance Variable Declaration

@interface MyClass : NSObject { !!!!!!!!!!!!!!!!!!! }

iOS Bootcamp


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

iOS Bootcamp


@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


@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


@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

Bad News

NO namespaces ☹ Use prefix instead !

NSObject, NSString, ... !UIButton, UILabel, ... !ABAddressBook, ABRecord, ... !// Pragma Mark PMDeveloper, PMEvent, ...

Draft Proposal for Namespaces in Objective-C: @namespace @using 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/

iOS Bootcamp

Method & Message

iOS Bootcamp

Method Declaration

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

iOS Bootcamp

Method Declaration


method scope

Can be either:

+ for a class method

- for an instance method

Methods are always public !

“Private” methods defined in implementation

iOS Bootcamp

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)

iOS Bootcamp

Method Declaration


method name

The method name is composed of all labels

Colons precede arguments, but are part of the method name

writeTofile:atomically:

iOS Bootcamp

Method Declaration


argument type

Arguments come after or within the method name

argument name

iOS Bootcamp

[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

Object Life Cycle

iOS Bootcamp

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

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 [auto]release

• When count equals 0, runtime invokes dealloc

dealloc

iOS Bootcamp

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-C http://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

iOS Bootcamp

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

Object Construction

• NSObject defines class method called alloc

• NSObject defines instance method called init

• alloc and init calls are always nested into single line

BankAccount *account = [BankAccount alloc];

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

[account init];

iOS Bootcamp

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

Property

iOS Bootcamp

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

Property Declaration@property(attributes) type name;

Attribute Impacts

readonly / readwrite Mutability

getter / setter API

nonatomic Concurrency

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

iOS Bootcamp


Attribute Impacts


getter / setter API



@property(readonly) NSString *accountNumber;

iOS Bootcamp


Attribute Impacts


getter / setter API



@property(getter=isActive) BOOL active;

iOS Bootcamp


Attribute Impacts


getter / setter API



@property(nonatomic, retain) NSDate *createdAt;

iOS Bootcamp


Attribute Impacts


getter / setter API



@property(readwrite, copy) NSString *accountNumber;

iOS Bootcamp

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

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

Property @implementation

#import "BankAccount.h" !@implementation BankAccount !//... !@synthesize accountNumber = _accountNumber; @synthesize balance = _balance; @synthesize fees = _fees; @synthesize active = _active; !//... !@end

iOS Bootcamp

Property @implementation

#import "BankAccount.h" !@implementation BankAccount !// No more @synthesize statements ! !!!!!!//... !@end

New in Xcode 4.4+

(WWDC 2012)

iOS Bootcamp

Protocol & Category

iOS Bootcamp

Protocol

• List of method declarations

• Define methods that others are expected to implement

• Conformance can be @required or @optional

Java / C# Interface done Objective-C style

iOS Bootcamp

Protocol

• Defining a Protocol

• Adopting a Protocol

@protocol NSCoding !- (void)encodeWithCoder:(NSCoder *)aCoder; - (id)initWithCoder:(NSCoder *)aDecoder; !@end

@interface Person : NSObject<NSCoding> { !} // method & property declarations @end

iOS Bootcamp

Category

• Add new methods to existing classes

• Does not define new instance variables

• Often used in defining “private” methods

Extending Object Features

iOS Bootcamp

#import "NSString+PMAddition.h" // ... NSString *string = @" A string to be trimmed"; NSLog(@"Trimmed string: '%@'", [string trim]);

Category• Defining and using a Category

// File NSString+PMAddition.m @implementation NSString (PMAddition) - (NSString *)trim { NSCharacterSet *s = [NSCharacterSet whitespaceAndNewlineCharacterSet]; return [self stringByTrimmingCharactersInSet:s]; } @end

// File NSString+PMAddition.h @interface NSString (PMAddition) - (NSString *)trim; @end

iOS Bootcamp

Base Types

iOS Bootcamp

Weak and Strong Typing

• Weak-Typed object:

• Strong-Typed object:

• Compile-time and run-time type checking:

• Weak-Typed: call not exiting method => run-time error

• Strong-Typed: call not exiting method => compile-time warning => run-time error

id anObject;

BankAccount *anObject;

iOS Bootcamp

The nil object pointer

• Test for nil explicitly or implicitly:

• Can use in assignments and as arguments if expected

• Sending a message to nil?

if (nil == person) { //

person = nil; [button setTarget:nil];

person = nil; [person talk]; // If it’s nil, do nothing (no error!)

if (!person) { //

iOS Bootcamp

• Root Class

• Implements many basics

• 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

iOS Bootcamp

• NSArray - ordered collection of objects

• NSDictionary - collection of key-value pairs

• NSSet - unordered collection of unique objects

Collections

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

iOS Bootcamp

• Collections can contain only objects

• Wrap primitive types in NSNumber or NSValue

• New literal syntax

Collections

NSArray *a = @[@"42", @42, @"42", @3.14]; !NSDictionary *d = @{ @1: @"black", @2: @"white"};

New in Xcode 4.4+

(WWDC 2012)

iOS Bootcamp

• Objective-C string literals start with @

• General-purpose Unicode string support

• NSString is immutable, NSMutableString is mutable

@”NSString”

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

Summary

iOS Bootcamp

• 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

#pragma mark

iOS Bootcamp

One More Thing !

iOS Bootcamp

\

[email protected]

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

Objective-C - IEEE UNIPV Student Branchieee.unipv.it/documents/Objective_C.pdf• Objective-C 2.0...

Documents

Transcript of Objective-C - IEEE UNIPV Student Branchieee.unipv.it/documents/Objective_C.pdf• Objective-C 2.0...