Objective -C for iOS application development

1. 1
Introduction to Objective-C
and
iPhone Development

2. 2
Introduction
• Objective-C is implemented as set of extensions
to the C language.
• It's designed to give C a full capability for object-oriented
programming, and to do so in a simple
and straightforward way.
• Its additions to C are few and are mostly based
on Smalltalk, one of the first object-oriented
programming languages.

3. 3
Why Objective C
• Objective-C incorporates C, you get all the benefits of C
when working within Objective-C.
• You can choose when to do something in an object-oriented
way (define a new class, for example) and when
to stick to procedural programming techniques (define a
struct and some functions instead of a class).
• Objective-C is a simple language. Its syntax is small,
unambiguous, and easy to learn
• Objective-C is the most dynamic of the object-oriented
languages based on C. Most decisions are made at run
time.

4. 4
Object-Oriented Programming
• The insight of object-oriented programming is to
combine state and behavior, data and
operations on data, in a high-level unit, an
object, and to give it language support.
• An object is a group of related functions and a
data structure that serves those functions. The
functions are known as the object's methods,
and the fields of its data structure are its
instance variables.

5. 5
The Objective-C Language
• The Objective-C language is fully
compatible with ANSI standard C
• Objective-C can also be used as an
extension to C++.
• Although C++ itself is a Object-Oriented
Language, there are difference in the
dynamic binding from Objective-C

6. 6
Objective-C Language (cont.)
• Objective-C source files have a “.m”
extension
• “.h” file is the interface file
• For example:
– main.m
– List.h (Interface of List class.)
– List.m (Implementation of List class.)

7. 7
ID
• “id” is a data type used by Objective-C to
define a pointer of an object (a pointer to
the object’s data)
• Any type of object, as long as it is an
object, we can use the id data type.
• For example, we can define an object by:
id anObject;
• nil is the reserved word for null object

8. 8
Dynamic Typing
• “id” data type has no information about the
object
• Every object carries with it an isa instance
variable that identifies the object's class,
that is, what kind of object it is.
• Objects are thus dynamically typed at run
time. Whenever it needs to, the run-time
system can find the exact class that an
object belongs to, just by asking the object

9. 9
Messages
• To get an object to do something, you
send it a message telling it to apply a
method. In Objective-C, message
expressions are enclosed in square
brackets
[receiver message]
• The receiver is an object. The message is
simply the name of a method and any
arguments that are passed to it

10. 10
Messages (cont.)
• For example, this message tells the myRect
object to perform its display method, which
causes the rectangle to display itself
[myRect display];
[myRect setOrigin:30.0 :50.0];
• The method setOrigin::, has two colons, one for
each of its arguments. The arguments are
inserted after the colons, breaking the name
apart

11. 11
Polymorphism
• Each object has define its own method but for
different class, they can have the same method
name which has totally different meaning
• The two different object can respond differently
to the same message
• Together with dynamic binding, it permits you to
write code that might apply to any number of
different kinds of objects, without having to
choose at the time you write the code what kinds
of objects they might be

12. 12
Inheritance
• Root class is NSObject
• Inheritance is cumulative.
A Square object has the
methods and instance
variables defined for
Rectangle, Shape,
Graphic, and NSObject,
as well as those defined
specifically for Square

13. 13
Inheritance (cont.)
• Instance Variables: The new object contains not only the
instance variables that were defined for its class, but
also the instance variables defined for its super class, all
the way back to the root class
• Methods: An object has access not only to the methods
that were defined for its class, but also to methods
defined for its super class
• Method Overriding: Implement a new method with the
same name as one defined in a class farther up the
hierarchy. The new method overrides the original;
instances of the new class will perform it rather than the
original

14. Primitive data types from C
• int, short, long
• float,double
• char
14

15. Operators same as C
• +
• -
• *
• /
• ++
• --
15

16. Address and Pointers
• Same as C
• To get address of a variable i
&i
• Pointer
int *addressofi = &I;
16

17. Conditionals and Loops
• Same as C/C++
• if / else if/ else
• for
• while
• break
• ontinue
• do-while
for(int i=0; i< 22; i++) {
NSLog(“Checking i =“%d”, i);
if(i == 12)
{ break;}
}
17

18. 18
for in loop
• Introduced in Objective-C 2.0 (“fast enumeration”)
for(Item_Type *item in Collection_of_Items) {
//do whatever with the item
Nslog(@” Looking now at %@”, item);
}

19. 19
Functions
• Same as C/C++
• return_type functionName(type v1, type v2, ….)
{ //code of function
}
Example
void showMeInfo(int age)
{
printf(“You are %d years old”, age); //or use NSLog()
}

20. 20
Global and static variables
• Same as C/C++
• Global variables defined at top of file
• For static variables use keyword static before it
static in CurrentYear = 2013;

21. Automatic Reference Counting
21
• Objective C uses ‘AUTOMATIC reference
counting' as memory management
• keeps an internal count of how many times
an Object is 'needed'.
• System makes sure that objects that are
needed are not deleted, and when an
object is not needed it is deleted.

22. 22
Defining a Class
• In Objective-C, classes are defined in two
parts:
– An interface that declares the methods and
instance variables of the class and names its
super class
– An implementation that actually defines the
class (contains the code that implements its
methods)

23. 23
The Interface
• The declaration of a class interface begins
with the compiler directive @interface and
ends with the directive @end
@interface ClassName : ItsSuperclass
{
instance variable declarations
}
method declarations
@end

24. 24
Declaration
• Instance Variables
float width;
float height;
BOOL filled;
NSColor *fillColor;
• Methods:
• names of methods that can be used by class objects,
class methods, are preceded by a plus sign
+ alloc
• methods that instances of a class can use, instance
methods, are marked with a minus sign:
- (void) display;

25. 25
Declaration (cont.)
• Importing the Interface: The interface is
usually included with the #import directive
#import "Rectangle.h"
• To reflect the fact that a class definition builds on
the definitions of inherited classes, an interface
file begins by importing the interface for its super
class
• Referring to Other Classes: If the interface
mentions classes not in this hierarchy, it must
declare them with the @class directive:
@class Rectangle, Circle;

26. 26
Creating class instances
ClassName *object = [[ClassName alloc] init];
ClassName *object = [[ClassName alloc] initWith* ];
– NSString* myString = [[NSString alloc] init];
– Nested method call. The first is the alloc method called on NSString itself.
This is a relatively low-level call which reserves memory and instantiates
an object. The second is a call to init on the new object. The init
implementation usually does basic setup, such as creating instance
variables. The details of that are unknown to you as a client of the class.
In some cases, you may use a different version of init which takes input:
ClassName *object = [ClassName method_to_create];
– NSString* myString = [NSString string];
– Some classes may define a special method that will in essence call alloc followed by
some kind of init

27. 27
Example: Hello World
#import <Foundation/Foundation.h>
int main (int argc, const char * argv[]) {
NSAutoreleasePool * pool =
[[NSAutoreleasePool alloc] init];
// insert code here...
NSLog(@"Hello, World!");
[pool drain];
return 0;
}
NSLog() is equivalent to a C printf()
Very similar to C
C programs are valid in Objective-C

28. 28
Intro to HelloWorld
• Objective-C uses a string class similar to the
std::string or Java string. It is called NSString.
• Constant NSStrings are preceded by @ for
example: @”Hello World”
• You will notice that NSLog() also outputs time
and date and various extra information.
• NSAutoreleasePool* pool =[[NSAutoreleasePool
• alloc] init]; allocates a lump of memory
• Memory must be freed with [pool drain];

29. 29
Some things to note
• No line break needed at end of NSLog
statements.
• NSString constants use C-style variables.
• Test this program to see results.

30. 30
@interface
@interface ClassName : ParentClassName
{
declare member variable here;
declare another member variable here;
}
declare method functions here;
@end
• Equivalent to C class declaration
• Goes in header (.h) file
• Functions outside curly braces
• Don’t forget the @end tag

31. 31
@implementation
#import <Foundation/Foundation.h>
#include "ComputerScience.h“
@implementation ClassName
define method function here;
define another method function here;
define yet another method function here;
@end
● Equivalent to C class function definitions
● Goes in source (.m) file
● Don't forget the @end tag

32. 32
Some things to note
• NSObject is the “root” object in Objective-C
• No direct access to instance variables so we write
some get/set “instance methods”
• Instance methods (affect internal state of class)
are preceded with a minus sign
• “Class methods” (higher level functions) are
preceded with a plus sign e.g. create new class
• Method return type in parentheses
• Semicolon before list of parameters
• Parameter type in parenthesis, followed by name

33. 33
Data Structures
• Objective-C arrays are similar to C arrays, but
you can initialize whole array in a list.
• Or just a few indices of the array. The rest are
set to 0.
• Or mix and match; the example will create an
array of size [8].
int values[3] = { 3, 4, 2 };
char letters[3] = { 'a', 'c', 'x' };
float grades[100] = {10.0,11.2,1.1};
int array[] = {[3]=11,[2]=1,[7]=0};

34. 34
Multi-dimensional Arrays
• Can be initialized by using subset notation with
braces. Note no comma after second subset.
• Subset braces are optional, the compiler will fill
in blanks where it can as with 1D arrays.
int array[2][3] = {
{ 0, 3, 4},
{ 1, 1, 1}
};
int array[2][3] = {0, 3, 4, 1, 1, 1};

35. 35
Frameworks
• UIKit.framework for developing standard iOS GUIs
(buttons etc.)
• UITextField (user-entered text that brings up the
keyboard)
• UIFont
• UIView
• UITableView
• UIImageView
• UIImage
• UIButton (a click-able button)
• UILabel (a string of text on-screen)
• UIWindow (main Window on iPhone)