 Class:
 defines the grouping of data and code type of entity 
 Object or Instance:
 a specific instantiation of a class with its own state (class variables values)
 Method:
 a “function/operator” that an object knows how to perform
 Instance Variable:
 this is what we call class variable in other OOP languages

 Strict superset of C
 Mix C with ObjC
Or even C++ with ObjC (usually referred to as ObjC++) 
 A very simple language, but some new syntax
 Single inheritance, classes inherit from one and only one superclass
 Protocols define behavior that cross classes
 Dynamic runtime
 Loosely typed, if you’d like

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•
•
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What’s most confusing about Objective-C?
Most class names start with NS: NSString, NSObject
Parameter lists are not comma delimited and method names are interrupted by parameter names and types.
There are too many brackets and colons. :[
Memory Management.
All these @ symbols confuse me.
Both C and Objective-C methods are allowed? Weird.

Instances/Objects respond to instance methods
 - (id)init;
 - (float)height;
 - (void)walk;
[object walk]
Classes respond to class methods
 + (id)alloc;
 + (id)person;
 + (Person *)sharedPerson; [ClassName person]

void doNothing () {
// nothing
}
} int addThree ( int x ) { return x + 3;
} int multiplyThreeParameters ( int x , int y , int z ) { return x * y * z;
Key return type method name parameter type parameter name
// note methods with multiple parameters are given in a parameter list
// that is delimited by commas .

}
}
- ( void ) doNothing {
// nothing
Key return type method name parameter type parameter name
- ( int ) addThree: ( int ) x { return x + 3;
}
- ( int ) multiplyThis: ( int ) x ByThis: ( int ) y AndThis: ( int ) z { return x * y * z;
NOTE: methods of Objective-C classes with multiple parameters have a to delimit the end of the parameter name and the continuation of the method name.
Actually method name is multiplyThis:ByThis:AndThis

}
- ( int ) multiplyThis: ( int ) x ByThis: ( int ) y AndThis: ( int ) z { return x * y * z;
Method name is

object.
method ( param1 , param2 );
object-> method ( param1 , param2 );
(no objects) method ( param1 , param2 );
[ object method: param1 method: param2 ];
Only a space between no comma

[ object method: param1 method: param2 ];
Example:
If you have a string:
NSString * msg = @"ALL YOUR BASES BELONG TO US" ;
And you want to split the sentence into an array of words:
NSArray * words = [ msg componentsSeparatedByString: @" " ];
// The @ is required for all string literals, and encodes the string using
UTF8

Object o = new Object ();
// Java takes care of garbage collection. In this statement, memory
// is automatically allocated for the new object. Memory is also
// automatically released when the object is no longer in use.
Object * o = ( Object * ) malloc ( sizeof ( Object )); free (o);
Object * o = new Object ; delete ( o );

Object * obj = [[ Object alloc] init];

 Asking other objects to create objects for you



NSString’s - (NSString *)stringByAppendingString:(NSString *)otherString;
NSString’s & NSArray’s - (id)mutableCopy;
NSArray’s - (NSString *)componentsJoinedByString:(NSString *)separator;
 Not all objects handed out by other objects are newly created




NSArray’s - (id)lastObject;
NSArray’s - (id)objectAtIndex:(int)index;
Unless the method has the word “copy” in it, if the object already exists, you get a pointer to it.
If the object does not already exist (like the 3 examples above), then you’re creating.
 Using class methods to create objects




NSString’s + (id)stringWithFormat:(NSString *)format, ...
UIButton’s + (id)buttonWithType:(UIButtonType)buttonType;
NSMutableArray’s + (id)arrayWithCapacity:(int)count;
NSArray’s + (id)arrayWithObject:(id)anObject;

 Allocating and initializing an object from scratch





Doing this is a two step process: allocation, then initialization.
Both steps must happen one right after the other (nested one inside the other, in fact).
Examples:
NSMutableArray *stack = [[NSMutableArray alloc] init];
CalculatorBrain *brain = [[CalculatorBrain alloc] init];
 About Allocating


Heap allocation for a new object is done by the NSObject class method + (id)alloc
It allocates enough space for all the instance variables (e.g., the ones created by
@synthesize).
 About Initializing
 Classes can have multiple, different initializers (with arguments) in addition to plain init.


If a class can’t be fully initialized by plain init, it is supposed to raise an exception in init.
NSObject’s only initializer is init.

 More complicated init methods


If an initialization method has arguments, it should still start with the four letters init
Example: - (id)initWithFrame:(CGRect)aRect; // initializer for UIView
UIView *myView = [[UIView alloc] initWithFrame:thePerfectFrame]; 
 Examples of multiple initializers with different arguments




From NSString:
- (id)initWithCharacters:(const unichar *)characters length:(int)length;
- (id)initWithFormat:(NSString *)format, ...;
- (id)initWithData:(NSData *)data encoding:(NSStringEncoding)encoding;
 Classes must designate an initializer for subclassers
 This is the initializer that subclasses must use to initialize themselves in their designated initializer.
 Static typing of initializers


For subclassing reasons, init methods should be typed to return id (not statically typed)
Callers should statically type though, e.g., MyObject *obj = [[MyObject alloc] init];

 Creating your own initialization method
 Super initializer can return nil if it failed to initialize.
 Example ---.m file
@implementation MyObject
}
{
- (id)init self = [super init]; // call our super’s designated initializer if (self) {
// initialize our subclass here
} return self;
@end

 In Java, students can define and implement a class in a single .java file.
 In C++, students define a class and methods in a .h header file and implement the methods in a .c file.
 In Objective-C, students define a class and its methods in a .h header file and implement the methods in a .m file.
Circle.h
include
Circle.m

Circle.h
@interface Circle : NSObject {
// instance variables double radius = 1.0;
}
// Class methods
+( double ) getPi ;
// Instance methods
-( double ) getArea ;
-( void ) setRadius: ( double ) r;
Key class name superclass return type method name parameter type parameter name
Optional parameter name @end

Circle.m
#import "Circle.h"
@implementation Circle
}
+(double) getPi { return 3.14159265;
}
-(double) getArea { double pi = [Circle getPi]; return pi * radius * radius;
-(void) setRadius:(double) r { radius = r;
}
@end

Main.m
#import "Circle.h"
// Non Objective-C function; program origin int main() {
}
}
@autoreleasepool
{
Circle *mycirc = [[Circle alloc] init];
[mycirc setRadius:3.0]; double area = [mycirc getArea]; double pi = [Circle getPi]; return 0;

 Have both definition file and implementation file : classname.h and classname.m

 When declaring or implementing functions for a class , they must begin with a + or -
 + indicates a “class method” that can only be used by the class itself. In other words, they’re for private functions ---like static functions in other languages.
 indicates “instance methods” to be used by the client program ( public functions) –invoked on objects/instance of class

#import <Cocoa/Cocoa.h>
@interface Node : NSObject {
Node *link; int contents;
}
+(id)new; node.h
Class is Node who’s parent is NSObject
-(void)setLink:(Node*)next;
-(int)getContent;
-(Node*)getLink;
@end
+/- private/public methods of Class
Class variables are private

#import "node.h”
@implementation Node
+(id)new
{ return [Node alloc];}
-(void)setContent:(int)number
{contents = number;}
-(void)setLink:(Node*)next {
[link autorelease]; link = [next retain];
}
-(int)getContent
{return contents;}
-(Node*)getLink
{return link;}
@end node.m
Like your C++
.cpp file
>>just give the methods here

ClassName *object = [[ClassName alloc] init];
OR
ClassName *object= [[ClassName alloc] initWith*];

object = nil;
Like NULL in
C ++
Like null in
Java
The underlying system will take care of removing the object from memory for you automatically.
Note: a lot of programs don’t explicitly set objects to nil but, is an option for you.

if (object == nill) //or if (object)
{ //do whatever }
Actually, in Objective-C if an objects is nil and you send a message (method call) to it does nothing….however, if you are expecting results and try to use them you could get in trouble –so checking in this case is important.

 Class Method call is like a STATIC method – call on the class itself
 Example for class NSDate –has class method “date” that will return pointer to an instance of NSDate associated with current date
NSDate *now = [NSDate date ];
 Instance method is like normal function – call on an object
 Example for class NSDate –has instance method “timeIntervalSince1970 ” that will return seconds of the date object since 1970 double seconds = [now timeIntervalSince1970];

 [receiver message]
 [receiver message:argument]
 [receiver message:arg1 andArg:arg2]
 Example of a Class method to construct and new object
NSDate *now = [NSDate date ];

 Message expression
 [receiver method: argument]
 Message
 [receiver method: argument ]
 Selector
 [receiver method: argument]
 Method
 The code selected by a message

[ Object methodp1:v1 methodp2:v2 methodp3:v3]
What is the actual method name? It is (yes it is odd!) methodp1:methodp2:methodp3
Example
NSCalendar *cal = [NSCalendar currentCalendar];
NSUInteger day = [cal ordinalityOfUnit:NSDayCalendarUnit forDate:now];
What is the name of the method ? It is ordinalityOfUnit:forDate

[[ Object method1] method 2] method 1 executed first and on the results method 2 is executed
Example without nesting
NSCalendar *cal = [NSCalendar currentCalendar];
NSUInteger day = [cal ordinalityOfUnit:NSDayCalendarUnit forDate:now];
Example WITH nesting
NSUInteger day = [[NSCalendar currentCalendar] ordinalityOfUnit:NSDayCalendarUnit forDate:now]

Person *voter; //assume this exists
[voter castBallot]; int theAge = [voter age];
[voter setAge:21]; if ([voter canLegallyVote]) {
}
// do something voter-y
[voter registerForState:@"CA“ party:@"Independant"];
NSString *name = [[voter spouse] name];

 Two kinds: setter methods and getter methods -
- used to set and get instance variables.
Example Person.h
@interface Person : NSObject
{
//two instance variables float heightInMeters; int weightInKilos;
}
- (void) setHeightInMeters :(float)h; //setter instance method
- (void) setWeightInKilos :(int)w; //setter instance method
- (void) weightInKilos ; //getter instance method
- (void) heightInMeters ; //getter insance method
NOTE: the convention of naming the setter methods as setVariableName
- (float) bodyMassIndex; //instance method
@end
NOTE: the convention of naming the getter methods same as the variable they access

Example Person.m
@implementation Person
- (float) heightInMeters
{ return heightInMeters; }
- (int) weightInKilos
{ return weightInKilos; }
- (void) setHeightInMeters:(float)h
{ heightInMeters = h; }
- (void) setWeightInKilos:(int)w
{ weightInKilos = w;}
- (float) bodyMassIndex
{ return weightInKilos / (heightInMeters * heightInMeters); }
@end

Example main.m
Int main(int argc, const char * argv[])
{
@autoreleasepool {
//Create an instance of Person
Person *person = [[Person alloc] init];
//Give instance variables some values
[person setWeightInKilos:96];
[person setHeightInMeters:1.8];
//Call bodyMassIndex method float bmi = [person bodyMassIndex];
NOTE: %f mean insert float value,
%d is an integer value --- same as you see in printf for C
//print out
NSLog(@”person (%d, %f) has a BMI of %f”,
[person weightInKilos], [person heightInMeters], bmi);

 Declare in one line the getter and setter methods for a variable
In Person.h add
Example -- new Person.h
@property
@interface Person : NSObject
{
//two instance variables float heightInMeters; int weightInKilos;
}
@property float heightInMeters ; //will create setter and getter method for this var
@property float weightInKilos ; //will create setter and getter method for this var
- (float) bodyMassIndex; //instance method
@end

 Declare in one line the getter and setter methods for a variable
Example -- new Person.h
@interface Person : NSObject
{
//don’t need to declare the variables here
// ---they are done with @property
}
@property float heightInMeters ; //will create setter and getter method for this var
@property float weightInKilos ; //will create setter and getter method for this var
- (float) bodyMassIndex; //instance method
@end

 Use @synthisize annotation new Person.m
#import “Person.h”
@implementation Person
@synthesize heightInMeters, weightInKilos;
Now in .m file must add
@synthesize annotation
- (float) bodyMassIndex
{ return weightInKilos / (heightInMeters * heightInMeters); }
Do not need to create the methods

 @property (a1,a2,*) var
Example
@property (nonatomic, readonly, strong) NSString *itemName;
 nonatomic / atomic = dealing with threading

 nonatomic = (YOU USE THIS FOR IOS), not thread-safe

NOTE: no problem if this is UI code because all UI code happens on the main thread of the application.
atomic = (don’t do this for iOS), thread safe, default
 readwrite/readonly

 readwrite= default value, declares both a setter and a getter.
readonly =means only create setter method.
 weak/strong/assign = dealing with memory management


 strong= strong reference to object stored in variable –see ARC weak = weak reference to object stored in variable –see ARC assign = default for variables that are primitive data types


//some code inside a method of a class float h = [self heightInMeters]; //method calss to getter for the variable heightInMeters
//another example a method in a class that adds itself (object) to an array that is passed
-(void) addYourselfToArray  NSMutableArray *) theArray
{ [theArray addObject:self]; }

 In .h file
}
{
@interface ClassName : ParentClass
//class variables
//methods
@end

 Create class Employee that has Person as parent and adds class variable of an employee id
Employee.h file
#import “Person.h”
{
@interface Employee : Person int employeeID;
}
@property int employeeID; //remember short cut to declare accessor methods
// for employeeID class variable
@end

 Can access Parent’s methods and variables
 Overriding methods
//Employee .m file
//override the
#import “Employee.h”
@implementation Employee
@synthesize employeeID; //remember this genearteds the setemployeeID() and employeeID() methods
- (float) bodyMassIndex //overridden method of previous Person parent class
{ return 19.0; }
@end
 super = keyword to mean parent class
- (float) bodyMassIndex //overridden method of previous Person parent class
{ float normalBMI = [super bodyMassIndex] ; //first call Person’s bodyMassIndex method return normalBMI*0.9;
}

 Primitive data types

 int age; float number;
 Object-type attributes


NSString myName;
NSNumber
 To-one relationship = point to a single “complex” object


Employee top_Employee;
Person spouse;
 To-many relationships = these are collections (objects or data)


NSMutableArray *friends;
NSArray *emails;

#import “Person.h”
Employee.h
{
@interface Employee : Person int employeeID; //primitive data
NSString *lastName; //object type
Person *spouse; //To-one more complex object
NSMutableArray *children; //To-many collections
}
//method declarations *****
@end
IMPORTANT
Have you noticed that object instance variables are always
Pointers to objects.

 Objects don’t live inside other objects.
 You only points from one object to another
 MePerson -> spouse (another Person)
 Result: you end up with a lot of distinct objects in your program’s memory
 Luckily we have Automatic Reference Counting for our iOS programs to take care of memory leaking and getting rid of no longer needed objects!!! Yes!

Suppose have Vehicle class and child Ship class
@interface Vehicle
- (void)move;
@end
@interface Ship : Vehicle
- (void)shoot;
@end
Ship *s = [[Ship alloc] init];
[s shoot];
[s move];
Vehicle *v = s;
[v shoot]; //THIS CAUSES a COMPILER WARNING –but not a runtime error

Suppose have Vehicle class and child Ship class id obj = ...;
[obj shoot]; //This is NOT a compiler warning
The compiler knows that the method shoot exists,
•possible that obj might respond to it --- NO compiler warning
•not typed obj enough for the compiler to be sure it’s wrong.
Will crash at runtime if obj is not a Ship
(unless is an object of some other class that implements a shoot method).

Suppose have Vehicle class and child Ship class id obj = ...;
[obj someMethodNameThatNoObjectAnywhereRespondsTo]; has never heard of this method.
COMPILER WARNING

Suppose have Vehicle class and child Ship class
NSString *hello = @”hello”;
[hello shoot];
The compiler knows that NSString objects do not respond to shoot.
crash at runtime .
COMPILER WARNING

Suppose have Vehicle class and child Ship class
NSString *hello = @”hello”;
Ship *helloShip = (Ship *)hello;
[helloShip shoot];
We are “casting” here.
The compiler thinks we know what we’re doing.
No compiler error as helloShip is thought to be a ship.. HOWEVER, it is not so, RUNTIME ERROR

 Base class for pretty much every object in the iOS SDK
 Methods
- (NSString *)description
 is a useful method to override (it’s %@ in NSLog()).
- (id)copy
 not all objects implement mechanism (raises exception if not)
- (id)mutableCopy
 not all objects implement mechanism (raises exception if not)

linkList.m
#import "linkList.h"
@implementation linkList
+(id)new
{return [linkList alloc];}
-(void)insert:(int)value { id temp = [Node new];
[temp setContent:value];
[temp setLink:head]; head = [temp retain];
[temp release];
}
Class linkList is child of previous Node class
-(void)append:(int)value { id last = [head getLink]; while ([last getLink] != nil)
{last = [last getLink];} id temp = [Node new];
[temp setContent:value];
[last setLink:temp];
[temp release];
}
-(void)remove { id temp = head; head = [head getLink];
[temp release];
}
-(int)getValue { return [head getContent];}
@end

Remember alloc creates the object in memory
#import "linkList.h”
#import "stack.h”
{}
+(id)new;
-(void)push:(int)value;
-(int)pop;
@end
+(id)new
{return [Stack alloc];}
-(void)push:(int)value
{[ self insert:value];} stack.h
-(int)pop { int ret = [ self getValue]; //getValue method of parent linkList
[ self remove]; //remove method of parent linkList return ret;
} stack.m
@end
Self is like the C++/Java word this.

#import "stack.h” new is the same as in C++/Java int main(){
Stack *s = [Stack new ];
[s push:1];
[s push:2]; printf("%d\t", [s pop]);
[s push:3]; printf("%d\t", [s pop]); printf("%d\t", [s pop]);
[s release]; return 0;
} main.c
$ gcc -x objective-c node.m linkList.m stack.m main.c -framework Cocoa -o stackTest
$./stackTest
2 3 1
Note only need to import “stack.h” because stack imports LinkList.h which imports Node.h which imports cocoa.h