Parte II Objective C

Objective-C
Ing. Paolo Quadrani
paolo.quadrani@gmail.com
www.mitapp.com

Introduction
• Runtime - Obj-C performs many tasks at runtime (object
allocation, method invocation)
→ require also a runtime environment ←
• Objects - An object associate data with operations that can
use or affect the data.
• id - General data type for any kind of object
• Object Messages - To get an object to do something, you
send it a message telling it to apply a method. Messages are
enclosed in brackets (e.g. [receiver message]; ). Methods in
message are called selectors.
• Classes - In Obj-C you define objects by defining their
class. The class definition is a prototype for a kind of object.
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Memory management

• Reference counting (retain, release)
• Manually managed or through the auto-
release pool
• Garbage collector (not used in iPhone
programming, but in Cocoa).


Class Interface
#import "ItsSuperclass.h"

@class anotherClassForwarding;

@interface ClassName : ItsSuperclass
{
// instance variable declarations
float width;
BOOL ﬁlled;
NSString *name;
}
// method declarations
- (void)setWidth:(ﬂoat)width;
+ (id)initWithName:(NSString *)aName;

@end


Class Implementation
@implementation ClassName : ItsSuperclass
{
//instance variable declarations
}

//method definitions
- (void)setWidth:(ﬂoat)width {
...
}

@end


Class Allocation
...

MyClass *obj = [[MyClass alloc] init];
obj->myVar = nil;

...


An Example
The difference between self and super becomes clear in a hierarchy of three

Messages to self and super
that we create an object belonging to a class called Low. Low’s superclass is M
All three classes define a method called negotiate, which they use for a var
Mid defines an ambitious method called makeLastingPeace, which also has n
This is illustrated in Figure 2-2:

Figure 2-2 High, Mid, Low

- reposition superclass

{ High – negotiate

...
[self negotiate];
...
superclass
}
Mid – negotiate
– makeLastingPeace

- reposition
{ superclass
...
Low – negotiate
[super negotiate];
...
}
We now send a message to our Low object to perform the makeLastingPea
makeLastingPeace, in turn, sends a negotiate message to the same Low
object self,

www.MitAPP.com http://paoloquadrani.blogspot.com/
- makeLastingPeace http://twitter.com/MitAPP
{

Class Initialization
• By convention initializer method begins with
init e.g. initWithColor: ...
• The return type should be id.
• You should assign self to the value returned by the
initializer.
• Setting value of member variables, use direct
assignment, not accessors.
• If initializer fails, return nil, otherwise return self.


Initializer Example

- (id)init {
// Assign self to value returned by super's designated initializer
// Designated initializer for NSObject is init
if (self = [super init]) {
creationDate = [[NSDate alloc] init];
}
return self;
}


Combining Allocation
and Initialization
• Some classes combine allocation and
initialization returning a new, initialized
instance of the class. Convenience
constructors
• Examples:+ (id)stringWithFormat:(NSString *)format

+ (id)arrayWithObject:(id)anObject;


Protocols
• Protocols declare methods that can be
implemented in any class.
Useful in:
• Declare methods that others are expected
to implement
• Declare the interface to an object
• Capture similarity among classes that are
not hierarchically related

Declaring Protocol
@protocol ProtocolName
// method declarations
@optional
// optional method declarations
@end

@protocol MyXMLSupport
- initFromXMLRepresentation:(NSXMLElement *)XMLElement;
- (NSXMLElement *)XMLRepresentation;
@end


Adopting a Protocol
@interface ClassName : ItsSuperclass < protocol list >

Ex:
@interface MyClass : NSObject <UITextFieldDelegate, UIAlertViewDelegate> {
...
}


Declared Properties

• Declared properties provides a way to
declare and implement an object’s accessor
methods
• The compiler can synthesize accessor
methods for you


Property declaration
and implementation
@property(attributes) type name;

@interface MyClass : NSObject
{
float value;
}
@property float value; - (float)value;
- (void)setValue:(float)newValue;
@end


Property Attributes
@property(attributes) type name;
• Writability
• readwrite (the default)
• readonly
• Setter Semantics
• assign (the default) - Used for scalar types such as NSInteger
• retain - Used for objects on assignment. The previous value is sent a
release.
• copy - A copy of the object is used for the assignment. The previous
value is sent a release.
• Atomicity
• nonatomic (by default) - The synthesized method provide robust access
in a multi-threading environment.

Example of Property
Declaration
@property (nonatomic, retain) IBOutlet NSButton *myButton;

@property (readonly) NSString *name;

@property (assign) UITextFieldDelegate *delegate;


Property
Implementation
• Provide one of these Implementation
Directives inside the @implementation block:
• @synthesize
• @dynamic
• Direct implement setter and getter
methods


Example using @synthesize

{ .h
NSString *value;
}
@property(copy, readwrite) NSString *value;
@end

@implementation MyClass .m
@synthesize value;
@end


Example using direct implementation
{ .h
NSString *value;
}
@property(copy, readwrite) NSString *value;
@end

@implementation MyClass

- (NSString *)value { .m
return value;
}

- (void)setValue:(NSString *)newValue {
if (newValue != value) {
value = [newValue copy];
}
}
@end


DEMO

• DEMO (10-15’):

Looking real code


Selectors

• In Objective-C selector has two meanings:
• It refers to a name of a method
• It refers to a unique identiﬁer that
replace the name when the code is
compiled


SEL and @selector

• Selectors are assigned to special type SEL
• Valid selectors are never 0
• @selector() directive lets you refer to
compiled selectors


Examples of selectors

SEL setWidthHeight;
setWidthHeight = @selector(setWidth:height:);

setWidthHeight = NSSelectorFromString(aBuffer);

NSString *method;
method = NSStringFromSelector(setWidthHeight);


Using a selector

• NSObject protocol deﬁnes three methods
that use selectors:
• performSelector:
• performSelector:withObject:
• performSelector:withObject:withObject:


Example
[friend performSelector:@selector(gossipAbout:)
withObject:aNeighbor];

is equivalent to:

[friend gossipAbout:aNeighbor];


Varying message at
runtime
• performSelector: and the other two allows
you to varying messages at runtime. Using
variables you can:

id helper = getTheReceiver();
SEL request = getTheSelector();
[helper performSelector:request];


Avoiding Messaging
Errors
• Selectors send a message to an object at
runtime
• An object that doesn’t implement a method
generate an error if someone try to send it
a request to execute a non existent
method
• respondsToSelector: is used to check the
existence of a method


Example

if ( [anObject respondsToSelector:@selector(setOrigin::)] )
[anObject setOrigin:0.0 :0.0];
else
fprintf(stderr, "%s can’t be placedn",
[NSStringFromClass([anObject class]) UTF8String]);


Using C++ with
Objective-C

• C++ can be used inside Objective-C code
• This hybrid is called Objective-C++
• Inheritance of Objective-C classes from C+
+ classes (and vice-versa) are not permitted


Example of mix
#import <Foundation/Foundation.h>
class Hello {
private:
id greeting_text; // holds an NSString
public:
Hello() {
greeting_text = @"Hello, world!";
}
Hello(const char* initial_greeting_text) {
greeting_text = [[NSString alloc]
initWithUTF8String:initial_greeting_text];
}
void say_hello() {
printf("%sn", [greeting_text UTF8String]);
}
};


Example (continue)
@interface Greeting : NSObject {
@private
Hello *hello;
}
- (id)init;
- (void)dealloc;
- (void)sayGreeting;
- (void)sayGreeting:(Hello*)greeting;
@end


Example (continue)
@implementation Greeting
- (id)init {
if (self = [super init]) {
hello = new Hello();
}
return self;
}
- (void)dealloc {
delete hello;
[super dealloc];
}
- (void)sayGreeting {
hello->say_hello();
}
- (void)sayGreeting:(Hello*)greeting {
greeting->say_hello();
}
@end


iPhone
Main UI arguments


Arguments

• Dealing with data: User Defaults, SQLite
• Touch events and Multi-Touch
• Address book
• Image Picker
• Localization

Dealing with data

• Property Lists
• iPhone File System
• Archiving Objects
• SQLite
• Web Services

Property Lists
• Convenient way to store small amount of data
• Array, dictionaries, strings, numbers
• XML or binary format
• NOT use it if
• data is more then few KB, loading is all or nothing
• Complex object graphs
• Custom object types


Reading-Writing
Property Lists
// Writing
- (BOOL)writeToFile:(NSString *)aPath atomically:(BOOL)ﬂag;
- (BOOL)writeToURL:(NSURL *)aURL atomically:(BOOL)ﬂag;

// Reading
- (id)initWithContentsOfFile:(NSString *)aPath;
- (id)initWithContentsOfURL:(NSURL *)aURL;


iPhone File System

• Each Application
• Has its own sand-box
• Has its own set of directories
• Can read-write within its own directory


File Paths in Your App
// Basic Directories
NSString *homePath = NSHomeDirectory();
NSString *tmpPath = NSTemporaryDirectory();

// Documents directories
NSArray *paths =
NSSearchPathForDirectoriesInDomain(NSDocumentDirectory,
NSUserDomainMask,YES);
NSString *documentsPath = [paths objectAtIndex:0];

// <Application Home>/Documents/foo.plist
NSString *fooPath =
[documentsPath stringByAppendingPathComponent:@”foo.plist”];


Include Writable Files in
Your Application
• Build it as part of your app bundle
• You can’t modify the content of your app
bundle, so:
• On ﬁrst launch, copy the writable to
your Documents directory


Archiving Objects
• Used for serialization of custom object types

• Used by Interface Builder for NIBs

• Archivable objects has to conform to the
<NSCoding> protocol

• Implement the two protocol methods:
- (void)encodeWithCoder:(NSCoder *)coder;
- (void)initWithCoder:(NSCoder *)coder;


Example Coder
// Encode an object for an archive
- (void)encodeWithCoder:(NSCoder *)coder {
[super encodeWithCoder:coder];
[coder encodeObject: name forKey:@”Name”];
[coder encodeIntger: numberOfSides forKey:@”Sides”];
}

// Decode an object from an archive
- (id)initWithCoder: (NSCoder *)coder {
self = [super initWithCoder: coder];
name = [[coder decodeObjectForKey: @”Name”] retain];
numberOfSides = [coder decodeIntegerForKey: @”Side”];
}


SQLite

• Complete SQL database in an ordinary ﬁle
• Simple, compact, fast, reliable
• No server is needed
• Great for embedded devices
• Included on the iPhone platform

When not to use
SQLite

• Multi-gigabyte database
• High concurrency (multiple writers)
• Client-server application


SQLite C API basic
• Open the DB
int sqlite3_open(const char *ﬁlename, sqlite3 **db);

• Execute a SQL statement
int sqlite3_exec(sqlite3 *db, const char *sql,
int (*callback)(void*, int, char **, char **),
void *context, char **error);

// Your callback
int callback(void *context, int count,
char **values, char **columns);

• Close the DB
int sqlite3_close(sqlite3 *db);


SQLITE 3
• DEMO (10-15’):

Real application with Sqlite3


Core Data
• Object graph management and persistence
framework
• Make it easy to save and load model objects
• Higher-level abstraction then SQLite or
property lists
• Available on the MAC OSX desktop
• Available only on iPhone OS 3.x and later


Integrating with Web Services
• Many are exposed via RESTful interface with XML
or JSON
• Options for Parsing XML are:
• libxml2 - C library
• NSXMLParser - simpler but less powerful
than the previous one
• JavaScript Object Notation
• More lightweight then XML
• Looks like a property list
• open source json-framework wrapper for Obj-C

JSON & XML PARSER
• DEMO (10-15’):

Real application with Json (Flickr API) & XML parser


Single Touch Sequence

• UITouch represent a single ﬁnger

• There are three phases in touch:

• touchBegan

• touchMoved

• touchEnded


UIEvent: Collection of UITouch

• UIEvent is a container for UITouch
• Can give information on:
• all touches
• all touches in a window
• all touches in a view

Receiving touches
• UIResponder is the base class of touches
‘listener’

• Methods called are:
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event;

- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event;

- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event;

- (void)touchesCancelled:(NSSet *)touches withEvent:(UIEvent *)event;


Multiple Touches

• Same events are generated then Single
Touch

• You must enable it to make it works
BOOL multipleTouchEnabled;


Address Book basics

• Create a person and set
some properties

• Create a
ABPersonViewController

• Push the view controller
onto the navigation stack


Get people from the
Address Book

ABAddressBookRef ab = ABAddressBookCreate();
CFArrayRef people = ABAddressBookCopyPeopleWithName(ab, name);


Person
• ABRecordRef
• A collection of properties
• First and last name
• Image
• Phone numbers, emails, etc...


Properties
• Properties can have different types

• String

• Date

• Dictionary, Data...

• Some properties may have multiple values

• Telephone: home, work, mobile...

• Person properties in ABPerson.h

Retrieve and Set Single
Value Properties

// Retrieve the ﬁrst name of a person
CFStringRef ﬁrst = ABRecordCopyValue(person, kABPersonFirstNameProperty);

// Update or Set the birthday of a person
CFDateRef date = CFDateCreate( ... );
ABRecordSetValue(person, kABPersonBirthdayProperty, date, &error);


Retrieve Multi Value
Properties (ABMultiValueRef)
// Getting multiplicity
CFIndex count = ABMultiValueGetCount(multiValue);

// and getting the value
CFTypeRef value = ABMultiValueCopyValueAtIndex(mv, index);

// and getting the lable
CFStringRef label = ABMultiValueCopyLabelAtIndex(mv, index);


Update Multi Value
Properties
// Get the multi value reference
ABMultiValueRef urls = ABRecordCopyValue(person, kABPersonURLProperty);

// Create the multi value mutable copy
ABMutableMultiValueRef urlCopy = ABMultiValueCreateMutableCopy(urls);

// Add the new value
ABMultiValueAddValueAndLabel(urlCopy, “the url”, “url label”, NULL);
ABRecordSetValue(person, urlCopy, kABPersonURLProperty);

// Save the Address Book
ABAddressBookSave(ab, &error);


Person View Controller
• ABPersonViewController
• displayedPerson
• displayedProperties
• allowsEditing


Image Picker Interface

• UIImagePickerController class
• Handles all user and device interactions
• Built on top of UIViewController
• UIImagePickerControllerDelegate protocol
• Implemented by your delegate object

Displaying the Image
Picker

• Check the source available
• Assign a delegate object
• Present the controller modality


Example Code

if([UIImagePickerController isSourceTypeAvailable:
UIImagePickerControllerSourceTypeCamera]) {
UIImagePickerController *picker =
[[UIImagePickerController alloc] init];
picker.sourceType = UIImagePickerControllerSourceTypeCamera;
picker.delegate = self;

[self presentModalViewController:picker animated:YES];
}


UIImagePickerController
delegate methods

• Two methods:
- (void)imagePickerController:(UIImagePickerController*)picker
didFinishPickingMediaWithInfo:(NSDictionary *)info;

- (void)imagePickerControllerDidCancel:
(UIImagePickerController*)picker;


Deﬁne your delegate
object
- (void)imagePickerController:(UIImagePickerController*)picker
didFinishPickingMediaWithInfo:(NSDictionary *)info {

// Save or use the image picked here.
UIImage *image = [info
objectForKey: UIImagePickerControllerOriginalImage];

// Dismiss the image picker.
[self dismissModalViewControllerAnimated:YES];
[picker release];
}


Deﬁne your delegate
object

- (void)imagePickerControllerDidCancel:
(UIImagePickerController*)picker {

// Dismiss the image picker.
[self dismissModalViewControllerAnimated:YES];
[picker release];
}


Manipulating the
returned Image

• If allowsImageEditing property is YES:
• User allowed to crop the returned image
• Image metadata returned in “info”
NSDictionary


Localizing an
Application
• Multiple Languages and locales in a single
built application
• Keep localized resources separate from
everything else
• Strings
• Images
• User Interfaces

Where do localized
resources do?
• MyApp.app/
• MyApp
• English.lproj/
• Localizable.strings
• MyView.nib
• Italian,lproj/
• Localizable.strings
• MyView.nib


Localized Strings
• For user-visible strings in application code
• Map from an non localized key to a
localized string
• Stored in .strings ﬁles
• Key-value pairs
• Use UTF-16 for encoding

Example of .strings

• en.lproj/Greetings.strings
“Hello” = “Hello”;
“Welcome to %@” = “Welcome to%@”;
• it.lproj/Greetings.strings
“Hello” = “Ciao”;
“Welcome to %@” = “Benvenuto a %@”;


Accessing localized
strings
// By default, uses Localizable.strings
NSLocalizedString(@”Hello”, @”Greeting for welcome screen”);

// Specify a table, uses Greetings.strings
NSLocalizedStringFromTable(@”Hello”, @”Greetings”,
@”Greeting for welcome screen”);


genstrings

• Tool to scan your code and produce
a .strings ﬁle
• Inserts comments found in code as clues to
localizer
• Run the tool over your *.m ﬁles


Localizing XIBs

• Xcode allows you to
generate localized
version of your User
Interface


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Parte II Objective C