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A Quick and Dirty Intro to
Objective C and iPhone
Programming
…or how I stopped worrying and learned to love Steve Jobs

What we’re going to cover
• Objective C basics
• iPhone library basics
• Writing an app
• Worshipping Steve Jobs

Objective C
• Another way of doing object oriented C
• Superset of the C language
• Uses the Smalltalk idea of message
passing rather than method invocation
• May look familiar to Vision users

Objective C
• Created in the early ’80s
• Adopted by NeXT in 1988
• Apple bought NeXT in 1996 and adopted
objective C as the language behind Mac
OS X

Message Passing
• Instead of calling a function we send
messages to our object;
Foo *myObject;
...
[myObject doThingsWithArg:argument];
Object Selector Argument

Function Declaration
• More new syntax:
-(void) doThingsWithArg:(int)anArg;
Method
“scope”
Return Type Selector Argument type Argument name

Class Definitions
• Split into two files
.h – header
.m - implementation

Foo.h:
@interface Foo : NSObject {
int anInt;
NSString *aString;
}
@end

Foo.m:
#import “Foo.h”
@implementation Foo
-(void) doThingsWithArg:(int)anArg {
…
}
@end

Constructors
• 2 part construction of objects
– Allocation: Allocation selector is “alloc”
– Initialisation: Initialisation selector is custom,
but always starts with “init” by convention.
• Constructors return ‘id’ type
• Standard construction line looks like:
[[myObject alloc] init];

Foo.h:
int anInt;
NSString *aString;
}
-(id) init;
-(id) initWithArg:(int)arg
andArg:(NSString*)arg2;
@end

Foo.m:
#import “Foo.h”
@implentation Foo
-(id) init {
return self;
}
andArg:(NSString*)arg2
{
anInt=arg;
aString=arg2;
return self;
}
-(void) doThingsWithArg:(int)anArg {…}
@end

Properties
• New in Objective C 2
– Released a couple of years back
• Automatic construction of accessors
• Must be declared in header and
‘synthesised’ in implementation

Foo.h:
int anInt;
NSString *aString;
}
-(id) init;
andArg:(NSString*)arg2;
@property (readwrite,assign) int anInt;
@property (readwrite,copy) NSString *aString;
@end

Foo.m:
#import “Foo.h”
@implentation Foo
@synthesize anInt;
@synthesize aString;
-(id) init {
[super init];
return self;
}
andArg:(NSString*)arg2
{
[super init];
myInstanceVar=arg;
aString=arg2;
return self;
}
-(void) doThingsWithArg:(int)anArg {…}
@end

Using our new object
Foo *myObj1=[[Foo alloc] init];
Foo *myObj2=[[Foo alloc] initWithArg:1
andArg:@”Pie”];
[myObj1 doStuffWithArg:23];
NSLog(@”%d and %@”,myObj2.anInt, myObj2.aString);
//prints out “1 and Pie”
NSLog(@”%d and %@”, [myObj2 getAnInt],
[myObj2 getAString]);
//also prints out “1 and Pie”

What was that assign/copy stuff?
• Objective C has a number of ways of
doing memory management
– Garbage collector
• New and not used everywhere
– Allocation pools
• Baby version of garbage collection
– Reference counting
• Used everywhere, including with pools and
garbage collection

• When you get an object its reference
count is 1
• Use “retain” to add one to the count
• Use “release” to drop one from the count
• When count hits zero the object is
destroyed
– Destructor method is called ‘dealloc’

A quick and dirty intro to objective c

• In properties you get to say how you want
the reference counts done
– Assign is a simple assignment, no reference
counting
– Retain returns the pointer to an object and
ups the reference count by 1 (for non-objects
this just works like assign)
– Copy returns a copy of the object

Reference counting
• This talk is called “quick and dirty”
because that’s all the memory
management I’m mentioning
• I’m still not sure when to retain things as
whether things are copied/retained/etc is
generally based on function naming
conventions.
– Lame

iPhone
• The iPhone uses Objective C and a bunch
of Apple libraries
• For many apps you can just bolt together
library bits with a little bit of extra logic and
data

The Steve says “LETS MAKE AN APP”

Going Further
• THE Cocoa programming book seems to
be:
Cocoa Programming for Mac OS X by Aaron Hillegass

Going Further
• Series of talks by Evan Doll and Alan
Cannistraro up on iTunes U
• Talks done at Stanford University in
Summer 2009 for the 2nd
year of their
iPhone programming course
• Missing some iPhone OS 3 features, but
very good.

Going Further
• Buy a Mac
• Make The Steve pleased
• Wear rollneck sweaters
• Conform
• Conform
• Conform
• Conform
• Conform
• Conform
• Conform

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A quick and dirty intro to objective c

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