Introduction to iOS and Objective-C

TECNOLOGIAS EMERGENTES EM JOGOS

Engenharia em Desenvolvimento de Jogos Digitais - 2013/2014

February 18, 2014

Daniela da Cruz

AGENDA
1. The iOS architecture

2

AGENDA
2. Objective-C
2.1

History

2.2

Objective-C primitives

2.3

Foundation Framework Data Types (Part I)

2.4

Pointers

2.5

Classes

2.6

Namespaces

2.7

Utilities

2

THE IOS ARCHITECTURE
→

iOS is the operating system that runs on iPad, iPhone, and
iPod touch devices.

→

At the highest level, iOS acts as an intermediary between the
underlying hardware and the apps we create.

→

Apps do not talk to the underlying hardware directly. Instead,
they communicate with the hardware through a set of
well-dened system interfaces.

→

These interfaces make it easy to write apps that work
consistently on devices having dierent hardware capabilities.

4

The implementation of iOS technologies can be viewed as a set of
layers.

5


→

Lower layers contain fundamental services and technologies.

→

Higher-level layers build upon the lower layers and provide
more sophisticated services and technologies.

6

THE IOS ARCHITECTURE CORE OS

The Core OS layer contains the low-level features that most other
technologies are built upon.

7

THE IOS ARCHITECTURE CORE OS
The layer provides a variety of services including:

→

low level networking;

→

access to external accessories;

→

and the usual fundamental operating system services such as
memory management, le system handling and threads.

8

THE IOS ARCHITECTURE CORE SERVICES

The iOS Core Services layer provides much of the foundation on
which the other layers are built.

9

THE IOS ARCHITECTURE CORE SERVICES

Key among these services are the Core Foundation and Foundation
frameworks, which dene the basic types that all apps use.
This layer also contains individual technologies to support features
such as location, iCloud, social media, and networking.

10

THE IOS ARCHITECTURE MEDIA

The Media layer contains the graphics, audio, and video
technologies you use to implement multimedia experiences in our
apps.
The technologies in this layer make easier to build apps that look
and sound great.

11

THE IOS ARCHITECTURE COCOA

The Cocoa Touch layer contains key frameworks for building iOS
apps.
These frameworks dene the appearance of your app.
They also provide the basic app infrastructure and support for key
technologies such as multitasking, touch-based input, push
notications, and many high-level system services.

12


2. Objective-C
2.1

History

2.2


2.3


2.4

Pointers

2.5

Classes

2.6

Namespaces

2.7

Utilities

14

HISTORICAL CONTEXT
→ 1972

→ 1980

→ 1983

→ 1986

C programming language
SmallTalk (rst OO language)
C++ (C extension with OO support)
Objective-C (C extension with concepts from

SmallTalk)

15

WHY OBJECTIVE-C?
→

Was chosen as the main language in NeXT company founded
by Steve Jobs to develop the operating System NeXTStep

→

In 1996, Apple buys NeXT and starting the development of
Mac OS X (2001) using Objective-C

Objective-C is the native programming language for Apple's iOS
and OS X operating systems.

16

OBJECTIVE-C
It's a compiled, general-purpose language capable of building
everything from command line utilities to animated GUIs to
domain-specic libraries.

17

OBJECTIVE-C
Objective-C is a strict superset of C, which means that it's possible
to seamlessly combine both languages in the same source le.
In fact, Objective-C relies on C for most of its core language

t's important to have at least a basic
foundation in C before tackling the higher-level aspects of the

constructs, so i
language.

18

OBJECTIVE-C
Like C++, Objective-C was designed to add object-oriented
features to C, but the two languages accomplished this using
fundamentally distinct philosophies.

→

Objective-C is more dynamic, deferring most of its decisions to
run-time rather than compile-time.

→

Objective-C is also known for its verbose naming conventions.

19

OBJECTIVE-C
C++
1

john-drive(Corvette, Mary's House)

Objective-C
1

[john driveCar:@Corvette toDestination:@Mary's House]

Objective-C method calls read more like a human language
than a computer one.

20

OBJECTIVE-C
As with plain old C programs, the

main()

function serves as the

root of an Objective-C application.

An autoreleasepool implements simple garbage collection for reference-counted objects. It temporarily
takes ownwership of reference-counted objects that nobody else wants to take ownership of and releases
them at a later, appropriate point in time.

21


2. Objective-C
2.1

History

2.2


2.3


2.4

Pointers

2.5

Classes

2.6

Namespaces

2.7

Utilities

22

ID TYPE
The

id

type is the generic type for all Objective-C objects. You can

think of it as the object-oriented version of C's void pointer
(void*).
And, like a void pointer, it can store a reference to any type of
object.

id mysteryObject = @An NSString object;

23

CLASS TYPE
Objective-C classes are represented as objects themselves, using a
special data type called

Class.

This lets you, for example, dynamically check an object's type at
runtime (introspection for later discussion).

Class targetClass = [NSString class];
id mysteryObject = @An NSString object;
if ([mysteryObject isKindOfClass:targetClass]) {
NSLog(@Yup! That's an instance of the target class);
}

24

SEL TYPE
The

SEL

data type is used to store selectors, which are

Objective-C's internal representation of a method name.
For example, the following snippet stores a method called

sayHello

in the

someMethod

variable. This variable could be used

to dynamically call a method at runtime.

SEL someMethod = @selector(sayHello);

25


2. Objective-C
2.1

History

2.2


2.3


2.4

Pointers

2.5

Classes

2.6

Namespaces

2.7

Utilities

26

FOUNDATION FRAMEWORK DATA TYPES (PART I)

NSObject

is the root class of most Objective-C class hierarchies.

Is the base class for pretty much every object in the iOS SDK.

27

FOUNDATION FRAMEWORK DATA TYPES
BOOL used for representing Boolean (YES or NO are BOOL
types allowed).

BOOL myBOOLyes = YES;
BOOL myBOOLno = NO;

28

NSString used for representing a string instead of C language's
char*
→
→

type.

An NSString instance

immutable.

can not be modied! They are

Tons of utility functions available (case conversion, URLs,
substrings, type conversions, etc.).

NSString* hi = @Hi;

29

NSMutableString Mutable version of NSString. (Somewhat
rarely used.)

NSMutableString * str1 = [NSMutableString
stringWithString:@Hello World];

30

NSNumber Object wrapper around primitive types like int,

float, double, BOOL,

etc.

NSNumber *num = [NSNumber numberWithInt:36];
float f = [num floatValue]; // would return 36 as a float
// (i.e. will convert types)

31

NSValue Generic object wrapper for other non-object data
types.

// CGPoint is a C struct
CGPoint point = CGPointMake(25.0, 15.0);
NSValue *pointObject = [NSValue valueWithCGPoint:point];

32

NSDate Used to nd out the time right now or to store past or
future times/dates.
An

NSDate

object represents a specic point in time, independent

of any particular calendrical system, time zone, or locale.
Internally, it just records the number of seconds from an arbitrary
reference point (January 1st, 2001 GMT).

NSDate *now = [NSDate date];

33


2. Objective-C
2.1

History

2.2


2.3


2.4

Pointers

2.5

Classes

2.6

Namespaces

2.7

Utilities

34

POINTERS

All Objective-C objects are referenced as pointers.
An NSString object must be stored as a pointer, not a normal
variable:

NSString *model = @Honda;

35

POINTERS
There is a slight dierence between C and Objective-C.
Whereas C uses

NULL,

Objective-C denes its own macro,

nil,

as

its null object.

NSString *anObject;
anObject = NULL;
anObject = nil;

// An Objective-C object
// This will work
// But this is preferred

int *aPointer;
aPointer = nil;
aPointer = NULL;

// A plain old C pointer
// Don't do this
// Do this instead

36

NIL VERSUS NULL

Objective-C's

nill

keyword is similar to

NULL

in other languages

like C and Java.
The dierence is that it is perfectly safe to call methods on
If any method that returns an object is called on
receive a

nil

nill,

nil.

we will

back.

37


2. Objective-C
2.1

History

2.2


2.3


2.4

Pointers

2.5

Classes

2.6

Namespaces

2.7

Utilities

38

CLASSES
When we dene a class, we dene a

blueprint for a data type.

This doesn't actually dene any data, but it does dene what the
class name means, that is:

→

what an object of the class will consist of; and

→

what operations can be performed on such an object.

39

CLASSES INTERFACE
An interface declares the public properties and methods of a class.

@interface Photo : NSObject
{
// Protected instance variables (not recommended)
}
// Properties and Methods
@end
Protected variables can be dened inside of the curly braces, but
most developers treat instance variables as implementation details
and prefer to store them in the

.m

le instead of the interface.

40

CLASSES INTERFACE
When declaring a method, ask yourself:

Does the method apply to only one instance or all instances
of the class?
If it applies to all instances, it's usually better as a class method.
Class methods are preceded by a minus (-) symbol.
Instance methods are preceded by a plus (+) symbol.
→

41

CLASSES INTERFACE
Example:

@interface Photo : NSObject
- (NSString*) caption;
- (NSString*) photographer;
- (void) setCaption: (NSString*)input;
- (void) setPhotographer: (NSString*)input;
@end

42

CLASSES IMPLEMENTATION
The

@implementation

directive is similar to

@interface,

except

you don't need to include the super class.

@implementation Photo {
// Private instance variables
}
// Methods
@end
The instance variables are

private and are only accessible inside the

class implementation.

43

Continuation of previous example:

@implementation Photo
{
NSString* caption;
NSString* photographer;
}
- (NSString*) caption { return caption; }
- (NSString*) photographer {
return photographer;
}
@end
44

The getters themselves are very simple. They just return the
instance variable.
A setter's job is to swap the old value with the new one.
Objective-C objects are dierent than an

int

or

float.

assign an object to a variable, it does not get the

reference to the object.

When you

value; it gets a

45


- (void) setCaption: (NSString*) input {
[caption autorelease];
[input retain];
caption = input;
}

46

1.

[caption autorelease]
We no longer need the old NSString object that caption refers
so, so we call autorelease on it.

2.

[input retain]
We call retain on the input object because we are going to
assign it to the instance variable and need it to stay around.

3.

caption = input
Finally we set the caption instance variable to be equal to
input.

47

DO I ALWAYS NEED TO DO THIS?

NO

but only if you choose

Automatic Reference Counting (ARC) to be
used in your project!!!

48

Classes usually have an

init

method to set initial values for its

instance variables or other setup tasks.

- (id) init {
[self setCaption:@Default Caption];
[self setPhotographer:@Daniela da Cruz];
}

return self;

49

1. Instance variables are set to

nil

automatically, so inside the

brackets, we set default values for

2.

photographer.
Any init method

caption

we create has to return

and

self

at the end.

Our implementation calls to the superclass version of

init

and captures the result, so we need to actually return the new
object to whoever requested it.

50

CLASSES INIT
Straight from

Apple's ocial documentation:

There are several critical rules to follow when implementing an

init

method that serves as a class's sole initializer or, if there are

multiple initializers, its

designated initializer:

1. Always invoke the superclass (super) initializer rst.
2. Check the object returned by the superclass. If it is
initialization cannot proceed; return

nil

nil,

then

to the receiver.

3. After setting instance variables to valid initial values, return
self.

51

CLASSES INIT
The basic format of a method to override the initializer looks as
follows:

-(id)init
{
self = [super init];
if (self != nil)
{
// Initialization code here
}
return self;
}

52

CLASSES DESIGNATED INITIALIZER
When working with a class that has more than one initialization
method, it's important that one of the initializers drives the whole
process.
Put another way,

only one of the initializer methods does the

actual work of calling the super class initializer and initializing the
instance variables of the object.
A general rule of thumb (although not always the case) is that the
designated initializer is the initializer with the most parameters.

53

@implementation Photo
// = Designated initializer =
-(id)initWithCaptionAndPhotographer: (NSString *)inCaption
photographer:(NSString *)inPhotographer
{
if (self = [super init])
{
[self setCaption:inCaption];
[self setPhotographer:inPhotographer];
}
return self;
}

54

-(id)initWithCaption: (NSString *)inCaption
{
return [self initWithCaptionAndPhotographer:inCaption
photographer:nil];
}
-(id)init
{
return [self initWithCaption:nil];
}
@end

55

CLASSES
Some notes:

→

All classes are derived from the base class called

→ NSObject
→

NSObject.

it is the superclass of all Objective-C classes.

It provides basic methods like memory allocation and
initialization.

→

Getters usually don't include the get keyword in method
name.

→

Init always return self at the end.

56


2. Objective-C
2.1

History

2.2


2.3


2.4

Pointers

2.5

Classes

2.6

Namespaces

2.7

Utilities

57

NAMESPACES

Objective-C does

not support namespaces, which is why the Cocoa

functions require prexes like NS, CA, AV, etc to avoid naming
collisions.
The recommended convention is to use a three-letter prex for your
application-specic classes (e.g., XYZCar).

58


2. Objective-C
2.1

History

2.2


2.3


2.4

Pointers

2.5

Classes

2.6

Namespaces

2.7

Utilities

59

UTILITIES NSLOG
NSLog is used for printing a statement.
It will be printed in device logs and debug console in release and
debug modes respectively.

Format Speciers:
→ %i, %d
→ %u
→ %f

→ %@

signed integer

unsigned integer
oat
object

60

Introduction to iOS and Objective-C

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