Objective-C is an object-oriented programming language that adds Smalltalk-style messaging to C. It allows programmers to define classes and objects that send and receive messages. Key features include classes and objects, memory management through retain counts, categories to add methods to classes, and protocols to define method requirements. Objective-C code uses square brackets [] to send messages between objects and uses dot syntax as a shorthand. Recommended resources for learning more about Objective-C include Apple's documentation and books focused on Cocoa and Objective-C.

1. Objective-C - an introduction
Spencer Pieters
RovingBird

2. RovingBird

3. RovingBird

4. RovingBird

5. RovingBird

6. RovingBird

7. Experience
C# C
Other C++
Objective-C
14%
4% 36%
43% 4%

8. Topics
History
Classes
Objects
Memory Management
OO
Interesting Bits
Recommended Books

9. popularity++;
June 2010, TIOBE index
“Despite the fact that Objective-C only gained
0.08% last month, it has entered the top-10 for
the first time.”

10. popularity++;

11. History
Created by Brad Cox and Tom Love
(StepStone, early 1980)
Licensed by NeXT
Used to build NeXTstep and project builder
Used in Mac OS X
Now: Xcode, Interface Builder, Cocoa

12. What ?
“Objective-C is a reflective, object-oriented programming
language which adds Smalltalk-style messaging to the C
programming language.”

13. Class Definition
@interface Classname: ItsSuperclass
{
instance variable definitions
}
+ (void)someMethod;
- (void)anotherMethod;
@end

14. Class Implementation
@implementation Classname
method definitions
@end

15. Objects
All objects are of type id
Every object has isa instance variable
Used by runtime to find out stuff about objects

16. Make objects do stuff
[receiver message];
Runtime resolves target of the message
Receiving object interprets message

17. Message examples
[myRect display];
[myRect setWidth:20];
[myRect setOriginX:10 y:20];

18. Messaging how-to
[object <keyword>:(type)<argument>]

19. Message examples
if (x.insersectsArc(35, 19, 23, 90, 120))

20. Message examples
if (x.insersectsArc(35, 19, 23, 90, 120))
if ([x intersectsArcWithRadius:35
centeredAtX:19
Y:23
fromAngle:90
toAngle:120])

21. Memory (1/3)
retainCount
new/alloc/copy: retainCount = 1
[object retain]: retainCount increase
[object release]: retainCount decrease

22. Memory (2/3)

23. Memory (2/3)
When retainCount becomes zero, object is free

24. Memory (3/3)
NSArray *cars = [[NSArray alloc] init...];
Car *car = [[Car alloc] init];
[cars addObject:car];
[car release];
car = nil;

25. Categories
Add new methods to existing classes without subclassing
@interface NSString (CategoryName)
- (NSString*)firstChar;
@end

26. Limitations
You can’t add instance variables to classes
Collisions in method names (prefixes)

27. Fast Enumeration
for (Type newVariable in expression)
{
statements
}
Expression conforms to NSFastEnumeration

28. Protocols
List of methods
Make a class conform to a protocol
Aka interfaces
@interface ClassName <ProtocolName>
@required
@optional
@end

29. Interesting bits
In Objective-C it is valid to send a message to nil
Boolean:YES/NO
No abstract/final classes
Exception handling via @try, @catch, @finally
No namespaces. Prefixes are used.

30. dot syntax
car.color = whatever;
[car setColor:whatever];
[car setValue:whatever forKey:@”color”];

31. Recommended Books

32. More recommended
http://developer.apple.com/library/mac/#documentation/
Cocoa/Conceptual/ObjectiveC/ObjC.pdf

33. Interested in Cocoa?
http://www.cocoaheads.be

34. More Info
www.rovingbird.com
spencer@rovingbird.com