introduction to objective c

Introduc)on to Objec)ve-‐C

Jussi Pohjolainen Tampere University of Applied Sciences

QUICKSTART

Background

•  Objec)ve-‐C is layered on top of the C – language – Based on SmallTalk-‐80 – Designed in early 1980s

•  NeXT SoLware licensed Objec)ve-‐C in 1988 •  Apple Computer acquired NeXT in 1996 •  Today: na)ve language for developing Mac OS X -‐ and iPhone -‐ apps

Class Declara)on: MyPoint.h

Class Implementa)on: MyPoint.m

Test the Class: main.m

Simple makefile MyPoint : MyPoint.m main.m

clang -fno-objc-arc -framework foundation MyPoint.m main.m -o MyPoint

run :

./MyPoint

clean :

rm MyPoint

Compiling and Running TB308POHJUS-L-2:point pohjus$ ls -al

total 32

drwxr-xr-x 6 pohjus staff 204 18 Tou 15:32 .

drwxr-xr-x 3 pohjus staff 102 18 Tou 14:52 ..

-rw-r--r--@ 1 pohjus staff 196 18 Tou 15:25 MyPoint.h

-rw-r--r--@ 1 pohjus staff 268 18 Tou 15:23 MyPoint.m

-rw-r--r--@ 1 pohjus staff 339 18 Tou 15:25 main.m

-rw-r--r--@ 1 pohjus staff 120 18 Tou 15:14 makefile

TB308POHJUS-L-2:point pohjus$ make

clang -fno-objc-arc -framework foundation MyPoint.m main.m -o MyPoint

TB308POHJUS-L-2:point pohjus$ make run

./MyPoint

2009-05-18 15:32:46.339 MyPoint[8725:807] X = 0 and Y = 0

2009-05-18 15:32:46.341 MyPoint[8725:807] X = 8 and Y = 7

TB308POHJUS-L-2:point pohjus$

Instan)a)ng an Object

// Declare a pointer to the object

MyPoint* point;

// Allocate memory for the object

point = [MyPoint alloc];

// Initialize the object

point = [point init];

Instan)a)ng an Object: One Liner

// Allocate and initialize the object

MyPoint* point1 = [[MyPoint alloc] init];

Messages (Methods)

- (void) setX: (int) n;!

method type: + = class method -‐ = object method

return type selector name

argument type

argument name

Messages, with Two Arguments

Declara=on - (void) setXAndY: (int) x: (int) y Usage [object setXAndY: 5: 6]; Declara=on, be@er way - (void) setX: (int) x andY: (int) y Usage [object setX: 5 andY: 6];

EXERCISES

MEMORY MANAGEMENT AND OBJECT LIFECYCLE

Memory Handling in General

•  When allocate something it must be released – Memory consump)on

•  In Java, garbage collector takes care of the release. Separate thread looking for objects that can be released

•  In Obj-‐C and C/C++, programmer is responsible about the release.

About Pointers

•  int a = 5; – Holds one integer value – The integer is stored in some memory address

•  Where? – You can get the memory address by using & in front of the variable: &a

Example of Memory Address int main(int argc, char *argv[]) { int a = 5; // prints 5 NSLog(@"%i", a); // prints something like 0x7fff5fbff9cc NSLog(@"%p", &a); return 0; }

Pointers

•  Pointer is a variable that stores memory address

•  int a; – holds integer variable

•  int* b; – holds memory address that points to integer value

•  int* b = &a; – Now b has the memory address of a

Example about Pointers #import "MyPoint.h" int main(int argc, char *argv[]) { int a = 5; // Store a's memory address to variable b int *b = &a; // prints 5 NSLog(@"%i", a); // prints something like 0x7fff5fbff9cc NSLog(@"%p", &a); // prints something like 0x7fff5fbff9cc NSLog(@"%p", b); // prints 5 NSLog(@"%i", *b); return 0; }

What is the result now? int main(int argc, char *argv[]) { int a = 5; // Store a's memory address to variable b int *b = &a; if(b == &a) { NSLog(@"Do we go here?"); } if(*b == a) { NSLog(@"What about here?"); } return 0; }

What is the result now? int main(int argc, char *argv[]) { int a = 5; int *b = &a; *b = 10; NSLog(@"%i", a); return 0; }

Memory Areas

•  Memory can be divided into three categories 1.  Global or sta)c 2.  Stack 3.  Heap

Sta)c

•  When something is in sta)c memory, it's there all the )me when app is running

•  So when star)ng the app, the memory is allocated an when the app closes, the memory is deallocated

•  The variable is stored in the same memory address all the )me.

Example of Sta)c Memory int thisIsStoredInStaticMemory = 5;

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

{

static int thisIsAlsoStoredInStaticMemory = 10;

NSLog(@"My number = %i", thisIsStoredInStaticMemory);

NSLog(@"My number = %i", thisIsAlsoStoredInStaticMemory);

return 0;

}

Stack -‐ Memory

•  Stack – memoryarea is usually small •  If you put too much "stuff" into stack, you might get stack overflow

•  Local variables are stored in stack! •  Variables are released when out of scope

Example of Stack Memory int main(int argc, char *argv[]) { int stack1 = 3; NSLog(@"My number = %i", stack1); if(YES) { int stack2 = 4; NSLog(@"My number = %i", stack2); // stack2 is released from memory now. } // stack1 is released from memory now. return 0; }

Example of Stack Memory int main(int argc, char *argv[]) { if(YES) { int stack2 = 4; } // Does this work? NSLog(@"My number = %i", stack2); return 0; }

Heap -‐ Memory

•  Heap – memory is the large memory area where almost all of the objects go.

•  Programmer is responsible for releasing the objects!

Example of Heap -‐ memory #import "MyPoint.h" int main(int argc, char *argv[]) { MyPoint* point = [MyPoint alloc]; //... [point release]; return 0; }

Crea)ng a Object

•  The crea)on of an object is done in two parts •  1) Alloca)ng memory –  MyPoint* point = [MyPoint alloc];

•  2) Ini)alize object state –  point = [point init];

•  Combined –  MyPoint* point = [[MyPoint alloc] init];

•  ó –  MyPoint* point = [MyPoint new];

What happens in Memory?

•  What happens in here? – MyPoint* p = [MyPoint alloc];

•  Two things! – MyPoint* p; – p = [MyPoint alloc];

•  p is in stack – memory! •  MyPoint object is in heap memory!

Problem? #import "MyPoint.h" int main(int argc, char *argv[]) { if(YES) { MyPoint* point = [MyPoint alloc]; } [point release]; return 0; }

Problem? #import "MyPoint.h" int main(int argc, char *argv[]) { MyPoint* point = [MyPoint alloc]; point = [MyPoint alloc]; [point release]; return 0; }

init-‐method? •  init-‐method is implemented in NSObject •  You can however implement your own init-‐method

- (id) initWithName: (NSString*) aName { if(self = [super init]) { name = aName; } return self; }

Other init-‐methods

•  Like in Java and C++, one can have mul)ple constructors

•  In Obj-‐C, one can have mul)ple init-‐methods -  (id) init -  (id) initWithX: (int) aX; -  (id) initWithX: (int) aX andY: (int) aY

Deallocing Object and Reference Count

•  Rules about reference coun=ng – When object is created its reference count is set to 1 –  Incremen)ng the reference count:

•  [point retain]; –  Decreasing reference count

•  [point release]; – When reference count reaches to 0, dealloca=ng occurs

•  ARC will save you from this!

Reference Count Example #import <Foundation/Foundation.h>

@interface Cat : NSObject

{

}

- (void) printMyRetainCount;

@end

@implementation Cat

- (void) printMyRetainCount

{

NSLog(@"Retain count = %i", [self retainCount]);

}

@end

Reference Count Example int main(int argc, char *argv[])

{

Cat* myCat = [[Cat alloc] init];

[myCat printMyRetainCount]; // Retain count = 1

Cat* reference = myCat;

[reference retain];


[myCat release];


[myCat release]; // Deallocation

return 0;

}

dealloc

•  You can implement a dealloc method

(void) dealloc

{

// Some code

[super dealloc];

}



{

NSString* name;

}

- (void) setName: (NSString *) theName

@end

@implementation Cat


{

name = theName;

}

@end


{

....

Cat* mirri = [[Cat alloc] init];

[mirri setName: someName];

// What happens now?

[someName release];

}

Since reference count is 0, dealloca)on occurs. This means, that the Cat does not have a name

anymore.



{

NSString* name;

}


@end

@implementation Cat


{

[name release];

name = theName;

[name retain];

}

@end


{

....

Cat* mirri = [[Cat alloc] init];

[mirri setName: someName];

// What happens now?

[someName release];

}

Since reference count is 1, dealloca)on does not occur and the Cat s)ll

has it's name.

Copying a Object

- (void)setName:(NSString *)theName

}

[name release];

name = [theName copy];

}

Autorelease Pool

•  Every Founda)on program must set up autorelease pool for the Founda)on objects

•  Pool keeps track of your objects for later release –  NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];

–  ... –  [pool drain];

Method Names

•  If method name includes alloc or copy, it returns a object that must be released –  // Must be released –  NSObject* object = [[NSObject alloc] init]; –  // Must be released –  NSObject* copy = [object copy]; –  // Do not have to release –  NSMutableString* string = [NSMutableString string];

•  The above string is released in Autorelease Pool!

Problem // Programmer A code

[[someObject giveCat] eat];

// Programmer B code

- (Cat*) giveCat

{

// Must be released!


// But where? Should the programmer who calls this method be

// responsible for deallocation of the Cat? How does the programmer

// know this?

return myCat;

}

..

Solu)on // Programmer A code [[someObject giveCat] eat]; // Programmer B code - (Cat*) giveCat {

// Must be released! Cat* myCat = [[Cat alloc] init]; // But where? When autopool is drained! [myCat autorelease]; return myCat; }

Delayed Release

•  Autorelease means "send release message later".

•  Release message is sent when Autorelease Pool is released

•  Autorelease Pool is created and released in UIKit programs automa=cally! – Pool is created at the beginning of an event cycle – Pool is released at the end of an event cycle

Autorelease Pools

App Loaded Wait for Event Handle event Exit app

Event loop

Pool created

Pool released

Autorelease Pool Usage // Method

- (Cat*) giveCat

{

// Must be released!


// But where? When autopool is drained!

[myCat autorelease];

return myCat;

}

// Usage

Cat* someCat = [object giveCat];

// someCat will be released in some time, so if you want to hold it, use

// retain

[someCat retain];

Rules

•  If method name contains "alloc", "new" or "copy", you must remember to use release or autorelease – Example: alloc, newObject, mutableCopy

•  If you retain something, you must use release or autorelease

•  Instance Variables: retain or copy •  autorelease means "send release later"

Cat.h #import <Foundation/Foundation.h> @interface Cat : NSObject { @private NSString* name; } - (id) initWithName: (NSString*) aName; - (void) setName: (NSString*) aName; - (NSString*) getName; - (void) dealloc; @end

Cat.m #import "Cat.h" @implementation Cat - (id) initWithName: (NSString*) aName { if(self = [super init]) { [self setName: aName]; } return self; } - (NSString*) getName { return name; }

- (void) setName: (NSString*) aName { if(aName != name) { [name release]; name = aName; [name retain]; } } - (void) dealloc { [name release]; [super dealloc]; } @end

main.m #import "Cat.h" int main(int argc, char *argv[]) { NSAutoreleasePool *pool =

[[NSAutoreleasePool alloc] init]; // Create the string NSString* catName = [[NSString

alloc] initWithString: @"Jack"]; // Create cat with the string Cat* cat = [[Cat alloc]

initWithName: catName]; // Just testing. This does not

deallocate catName! [catName release];

// Get the name NSString* name = [cat getName]; // Print the name NSLog(name); // Release name and cat [cat release]; [pool drain]; return 0; }

MANAGING MEMORY WITH ARC ARC to the rescue!

ARC?

•  ARC (Automa=c Reference Coun=ng) – Compiler does automa/c reference coun/ng by examining the source code and then add the retain and release messages to objects

•  Not garbage collec)on, no background process of dealloca)on of objects!

•  Inserts retain and release statements based on some fixed rules

•  OS X 10.7 and iOS 5 for all features

Object lose owners // Scenario 1 Person* jack = [[Person alloc] init]; jack = [[Person alloc] init]; // Scenario 2 Person* tina = [[Person alloc] init]; tina = nil;

// Scenario 3 if(yes) { Person* dave = [[Person alloc] init]; }

Some Fixed rules

•  If object is allocated and local to method, release statement is added near the end of that method

•  If allocated object is class a@ribute, release is added to dealloc

•  If the object is return value, it gets an autorelease statement

Guidelines

•  Don’t call! – retain, release, retainCount, autorelease or dealloc

•  You must use @autoreleasepool syntax •  You must enable ARC – clang -fobjc-arc -framework foundation Car.m Motor.m main.m -o App

makefile MyPoint : Car.m Motor.m main.m

clang -fobjc-arc -framework foundation Car.m Motor.m main.m -o App

run :

./App

clean :

rm App

main.m

motor.h

motor.m

PROPERTIES

Objec)ve-‐C 2.0: @property

Objec)ve-‐C 2.0: @synthesize

Objec)ve-‐C 2.0: Dot Syntax

Autosynthesize

Property Declara)on Aoributes: Writability

•  You can decorate a property with aoributes, example: – @property (readonly) int x;

•  readwrite –  Indicates that the property is read/write. Default

•  readonly – Only read – Generates only geoer method

Seoer Seman)cs •  assign –  Simple seoer. Default.

•  weak – Non-‐owning rela)onship with an object –  If object is deallocated, the property is set to nil

•  strong – Owning rela)onship with an object

•  copy –  Specifies that a copy of the object should be used for assignment

Seoer Seman)cs Examples // assign

property = newValue;

// copy

if (property != newValue)

{

[property release];

property = [newValue copy];

}

Atomicity

•  nonatomic – Specifies that accessor are non-‐atomic.

•  Proper)es are atomic by default: – [_internal lock]; – id result = [[value retain] autorelease]; – [_internal unlock]; – return id;

Motor.h

Main.m

Change! Car.h

STRINGS

About Strings

•  C String – char * // Array of characters

•  NSString – Object, that holds array of Unicode characters –  Is immutable, contents cannot be changed aLerwards!

•  NSMutableString – String that can be modified aLerwards

Crea)ng Strings // Simple way

NSString *temp1 = @"Hello World!";

// Appending, notice that this produces new string

NSString *beginning = @"beginning";

NSString *alphaAndOmega = [beginning stringByAppendingString:@" and end"];

Formapng

•  Formapng –  NSString *string1 = [NSString stringWithFormat:@"A

string: %@, a float: %1.2f", @"string", 31415.9265];

–  // string1 is "A string: string, a float: 31415.93"

•  Format Specifiers? – http://developer.apple.com/iphone/library/documentation/Cocoa/Conceptual/Strings/Articles/formatSpecifiers.html#//apple_ref/doc/uid/TP40004265-SW1

NSString methods

•  See: – http://developer.apple.com/documentation/Cocoa/Reference/Foundation/Classes/NSString_Class/Reference/NSString.html

NSMutableString methods

•  NSMutableString inherites NSString •  With NSMutableString you can modify the string with these methods

– appendFormat:

– appendString:

– deleteCharactersInRange:

– insertString:atIndex:

– replaceCharactersInRange:withString:

– replaceOccurrencesOfString:withString:options:range:

– setString:

PROTOCOLS

Protocols?

•  Compared to Java, protocols are interfaces •  You define methods that some object must implement

Using Protocols // MyProtocolName.h

// Notice that the protocol inherites NSObject

// protocol!

@protocol MyProtocolName <NSObject> //Method declarations go here

@end

// MyObject

@interface Class: NSObject <MyProtocolName>

Protocol as Variable •  In Java –  MyInterface object = new MyObject();

•  In Obj-‐C –  id<MyProtocolName> object = [[MyObject alloc] init];

•  As a method argument –  (void) doSomethingWithThisObject: (id<MyProtocolName>) aObject

•  ID is a predefined pointer type for an arbitrary object

FOUNDATION CLASSES

NSObject

•  NSObject is the root class of Most Obj-‐C classes

•  Crea)ng, copying, dealloca)ng objects

Collec)ons

•  Array: Ordered Collec/ons •  Dic)onary: Collec/ons of Keys and Values •  Set: Unordered Collec/ons of Objects •  Counted Sets: Unordered Collec/on of Indis/nct Objects

•  Enumera)on: Traversing a Collec/on's Elements

•  Mutable and immutable versions!

Other Classes

•  NSNumber, wrapper for standard number types

•  NSDate, NSCalendarDate

introduction to objective c

Technology

reference

framework

framework

reference

store

prints

memory address

char argv