1. An Objective‐C Primer
Babul Mirdha
Founder, Meetnar.com
www.meetnar.com

3. Overview
•Objective‐C
–a reflective,
fl i
–object‐oriented programming language
–follows ANSI C style coding
–that adds Smalltalk‐style messaging
that adds Smalltalk style messaging
–other C programming language.
Objective C
• Objective‐C
–a thin layer on top of C, and moreover is a strict
superset of C;
p
• it is possible
–to compile any C program with an Objective‐C
compiler,
–and to freely include C code within an Objective‐C
class.
class

4. • There is no formal written standard
– Relies mostly on libraries written by others
• Flexible almost everything is done at runtime.
– Dynamic Binding
Dynamic Binding
– Dynamic Typing
– Dynamic Linking

5. Inventors
• Objective‐C was invented by two men, Brad
j
y
,
Cox and Tom Love.
• Both were introduced to Smalltalk at ITT in
1981
• Cox thought something like Smalltalk would
be very useful to application developers
be very useful to application developers
• Cox modified a C compiler and by 1983 he had
a working Object oriented extension to C
a working Object‐oriented extension to C
called OOPC.

6. Development
• Tom Love acquired a commercial copy of
Tom Love acquired a commercial copy of
Smalltalk‐80 while working for Schlumberger
Research
• With direct access Smalltalk, Love added more
to OOPC making the final product, Objective‐
to OOPC making the final product Objective
C.
• I 1986 they release Objective‐C through their
In 1986 h
l
Obj i C h
h h i
company “Stepstone”

7. NeXT and NeXTSTEP
NeXT and NeXTSTEP
• In 1988 Steve Jobs acquires Objective‐C
q
j
license for NeXT
• Used Objective‐C to build the NeXTSTEP
Operating System
• Objective‐C made interface design for
NeXTSTEP much easier
much easier
• NeXTSTEP was derived from BSD Unix
• In 1995 NeXT gets full rights to Objective C
In 1995 NeXT gets full rights to Objective‐C
from Stepstone

8. OPENSTEP API
OPENSTEP API
• Developed in 1993 by NeXT and Sun
p
y
• An effort to make NeXTSTEP‐like Objective‐C
implementation available to other platforms.
• In order to be OS independent
– Removed dependency on Mach Kernel
– Made low‐level data into classes
• Paved the way for Mac OS X, GNUstep

9. Apple and Mac OS X
Apple and Mac OS X
• NeXT is taken over by Apple in 1996 and put
y pp
p
Steve Jobs and his Objective‐C libraries to
work
• Redesigned Mac OS to use objective‐C similar
d
d
b
l
to that of NeXTSTEP
• Developed a collection of libraries named
Developed a collection of libraries named
“Cocoa” to aid GUI development
Release Mac OS X (ten), which was radically
• Release Mac OS X (ten) which was radically
different than OS 9, in March 2001

10. The Cocoa API
The Cocoa API
• Primarily the most frequently used frameworks
Primarily the most frequently used frameworks
nowadays.
• Developed by Apple from NeXTSTEP and OPENSTEP
p
y pp
• Has a set of predefined classes and types such as
NSnumber, NSstring, Nsdate, etc.
g
• NS stands for NeXT‐sun
j
,
• Includes a root class NSObject where words like alloc,
retain, and release come from

11. Dynamic Language
Dynamic Language
•
•
•
•
Almost everything is done at runtime
Almost everything is done at runtime
Uses dynamic typing, linking, and binding
This allows for greater flexibility
hi ll
f
fl ibili
Minimizes RAM and CPU usage

12. Objective‐C Primer, Part 1

13. C++/C#/Java and Objective‐C
Terminology Comparison
Terminology Comparison

14. A brief introduction
A brief introduction
– Object model
Object model
– Square brackets
– Naming conventions
Naming conventions
– Importing
– Class definition and implementation
Class definition and implementation
– Exception handling
– Nil objects
Nil objects
– Memory management

15. Object Model
Object Model
• provides messaging‐style syntax that involves
provides messaging style syntax that involves
passing messages to object instances, rather
than calling methods on objects.
than calling methods on objects

16. Square Brackets and Methods
• The object model is based around the concept
The object model is based around the concept
that objects are sent messages in order to
invoke a method.
• The square brackets indicate that you are
The square brackets indicate that you are
sending a message to an object.
• Example:
[ diesel start];
[ diesel start];

17. Methods and Messaging
This declaration is preceded by a minus (-) sign, which indicates
that this is an instance method.
[myArray insertObject:anObject atIndex:0];

18. Calling a Method
// Create reference to an object of type Engine class called diesel.
Engine* diesel;
*
// Create an instance of the Engine object and point the diesel reference at it
diesel = [[ Engine alloc] init];
diesel [[ Engine alloc] init];
// Call the start method by passing the Engine object the start message
[ diesel start];
[ diesel start];
The same code in C++ (without the comments) would look as follows:
Engine diesel;
g
;
diesel = new Engine();
diesel.start();

19. Passing and Retrieving
• Passing:
[diesel start: gas];
• return such a value:
currentRevs = [ diesel revs ];

20. Naming Conventions
• much like other languages
much like other languages,
– using PascalCase for classes
– and camelCase for methods and properties
and camelCase for methods and properties.

21. Importing
•
Two ways of importing, just as with C/C++.
Two ways of importing just as with C/C++
–
–
•
1. Angle Bracker <>
2. Double Quote “”
The difference is that the syntax of
–
–
force the compiler’s preprocessor to look for the file in the system header directory,
Quotes syntax will look in the current directory if you haven’t specified an alternative location.
•
To look in the system header directory, use the following syntax:
•
#import <Foundation/foundation.h>
•
To look for your own header file in the current or specific directory, use the following syntax:
•
#import "myfile.h”

22. Class Definition and Implementation
Class Definition and Implementation
• As with most object‐oriented languages,
– an object is defined by its class,
– and many instances of that object may be created.
• Every class consists of
– an interface, which defines the structure of the class
– and allows its functionality to be implemented.
• Each class
Each class
– has a corresponding implementation
– that actually provides the functionality.

23. Obj‐C
Class with structure & Implementation
l
h
l
• In Obj‐C, these implementations are held in separate files,
with
– the interface code contained in a header file (.h extension)
– and the implementation held in a message file (.m extension).
• .h file:
– describes the Structure or Abstraction
• .m file:
.m file:
– implements details

25. Class in Obj C
Class in Obj‐C
Engine.h
Engine h
@interface Engin
‐ (int) revs;
@end
Engine.m
@implementation Engin
‐ (int) revs (
return revs;
}
‐ (void) start {
// Start the engine at an idle speed of 900 rpm
// – NOTE This is a comment
revs=900;
900
}
@end

26. Nil Objects
Nil Objects
• Methods are
– implemented as messages being passed to objects whose
correct identity is resolved at runtime.
• a mismatch during runtime,
– either an exception will be thrown (best‐case scenario)
– or the object will silently ignore the message (worst‐case
h b
ll l l
h
(
scenario).
• Be extra careful about both
– ensuring messageobject interaction is valid
– and that good exception handling is added throughout
and that good exception handling is added throughout.

27. Exception Handling
•
Similar to those used C++/C#/Java or exception handling in other
languages.
languages
@try
{
// Code to execute and for which you wish to catch the exception
}
@catch ()
{
// Do something after an exception has been caught
}
@finally
{
// Clean up code here
}

28. Memory Management
Memory Management
• A referencecounting system is used by Objective‐C.
•
• This means that
– if you keep track of your references, the runtime will automatically
reclaim any memory used by objects once the reference count returns
l i
d b bj t
th
f
t t
to zero.
• NSString* s = [[NSString alloc] init]; // Ref count is 1
NSString s [[NSString alloc] init]; // Ref count is 1
• [s retain]; // Ref count is 2 ‐ silly
• // to do this after init
• [s release]; // Ref count is back to 1
• [s release]; // Ref count is 0, object is freed

29. ARC
•
•
Now you are free from Reference counting because of ARC
Xcode 4.2 and iOS 5
–
–
offer a new feature called automatic reference counting (ARC),
which simplifies memory management.
• ARC
–
–
–
–
ARC makes memory management much easier,
greatly reducing the chance for your program to have memory leaks.
inserts the appropriate method calls for you at compile time.
The compiler also generates the appropriate dealloc methods to free
up memory that is no longer required.
• Essentially, ARC is a pre‐compilation stage that adds the necessary
code you previously would have had to insert manually.
code you previously would have had to insert manually

30. Objective‐C Primer, Part 2
Obj i C i
2

31. Class Declaration
Class Declaration
.NET C#
Objective‐C
cass AClass : Object
{
int aValue;
void doNothing();
g()
String returnString();
}
@interface AClass : NSObject
{
int aValue;
}
‐ (void)doNothing();
+ (NSString)returnString();
@end

32. Method Declaration
• Two type of Method:
– Class Method
– Instance method
• A class method
– indicated by a plus (+) character.
– associated with the class type.
• An instance method
– indicated by a minus (‐) character
indicated by a minus (‐) character.
– associated with an instance object associated with the
class.

35. Properties

36. Strings

37. Interfaces and Protocols

39. Comments

40. Demo
Hello World!

41. Creating Your First iPhone
Creating Your First iPhone Application
•
•
•
•
•
1. Create your project.
1 Create your project
2. Design your application.
3. Write code.
3
i
d
4. Build and run your app.
5. Test, measure, and tune your app.

42. Q & A

43. Thank You All