Objective oriented programming

• Class: type; declare state and behavior; defines the grouping of data and code; blueprint to create instances
• State(data): maintained using by instance variables
  • Instance: specific allocation of a class
  • Instance Variable(ivar): a specific piece of data belonging to an object, typically hidden
• Behavior, implemented by methods
  • Method: a function of how to perform

• Encapsulation: keep implementation private and separate from interface
• Polymorphism: different objects, same interface
• Inheritance: hierarchical organization in which a subclass inherits the behavior of a superclass

Objective-C 2.0 Programming language A guideline by Apple Developers

Message syntax

• Instances --
• Classes ++

Person *voter; //assume this exists 
[voter castBallot]; 
int theAge = [voter age]; 
[voter setAge:21];
if ([voter canLegallyVote]) { 
// do something voter-y
} 
[voter registerForState:@"CA" party:@"Independant"]; 
NSString *name = [[voter spouse] name];

• Dot syntax: [person height] equivalent to person.height

Types

• Dynamic/static(*): compile-time type checking, Obj-C always uses dynamic binding
• Null object pointer: =nil;
• BOOL typedef: =YES/NO;
• Selectors SEL: e.g. SEL sel = @selector(start:);

Class introspection

//inquire an object about its class
Class myClass = [myObject class];
NSLog(@"My class is %@", [myObject className]);
 
//testing for general class membership (subclasses included):
if ([myObject isKindOfClass:[UIControl class]]) { 
// something
}
 
//testing for specific class membership (subclasses excluded):
if ([myObject isMemberOfClass:[NSString class]]) { 
// something string specific
}

Objects

• Identity: testing whether the pointer values are the same

if (object1 == object2)

• Equality: testing object attributes

if ([object1 isEqual: object2])

• String object to be preceded by %/@

e.g. [NSString stringWithFormat: @"The answer is: %@", myObject];

Foundation Framework

• NSObject: root class; memory management, introspection, object equality
• NSString: general-purpose Unicode string
  • NSLog: equivalent to printf
  • common methods: (BOOL)isEqualToString: (NSString *)string;, (BOOL)hasPrefix: (NSString *)string;, (int)intValue;, (double)doubleValue;

NSString *aString = @"Hello World!";
if ([aString hasPrefix:@"He"]) {
   // will make it here
}

• NSMutableString
  • Collections: array, dictionary(collection of key-value pairs), set
  • common enumeration mechanism
• NSArray: nil termination

Classes

Class definition

.h public header

.m private implementation

=== e.g. Header:Person.h ===
#import <Foundation/Foundation.h>
 
@interface Person : NSObject 
{
  // instance variables 
  NSString *name; 
  int age;
}
 
// method declarations 
- (NSString *)name; 
- (void)setName:(NSString *)value;
 
- (int)age; 
- (void)setAge:(int)age;
 
- (BOOL)canLegallyVote; 
- (void)castBallot;
@end

=== e.g. Implementation:Person.c ===
#import "Person.h"
 
@implementation Person
 
- (BOOL)canLegallyVote {
  return ([self age] >= 18);
} 
 
- (void)castBallot {
  if ([self canLegallyVote]) {
    // do voting stuff
  } else { 
    NSLog (@“I’m not allowed to vote!”);
  }
} 
@end

• Superclass methods

[super doSomething];

Object

• +alloc allocate memory to store the object
• +init initialize object state

Person *person = nil;
person = [[Person alloc] init];

• Reference counting
  • object alive if retain count > 0
  • +alloc|-copy : retain count = 1
  • -retain: count++
  • -release: count--
  • if retain count=0, -dealloc invoked automatically
  • -autorelease: releases later/after return (in the last stage of handle event cycle)

Person *person = [[Person alloc] init];
// Retain count begins at 1 with +alloc
[person retain];
// Retain count increases to 2 with -retain
[person release];
// Retain count decreases to 1 with -release
[person release];
// Retain count decreases to 0, -dealloc automatically called

• Properties: access to object attributes
  • getter/setter methods implementation
  • specify read-only vs. read-write

@property int age; // read-write by default 
 @property (readonly) BOOL canLegallyVote;
 
// Memory management policies (only for object properties)
@property (assign) NSString *name; // pointer assignment 
@property (retain) NSString *name; // retain called 
@property (copy) NSString *name;	// copy called

• Dot syntax

@implementation Person 
- (void)doSomething {
  name = @“Fred”; 
  self.name = @“Fred”;
}

Controls

• Delegation: control passed to delegate objects to perform application-specific behavior

Anatomy

1. Model = data & state
2. View = UI
3. Controller = intermediary between model & view

Nib files: layout user interface elements, add controller objects, connect controller & UI

Controls and target-action

- (void)actionMethod; 
- (void)actionMethod:(id)sender; 
- (void)actionMethod:(id)sender withEvent:(UIEvent *)event;

• iTunes Connect
• iOS Provisioning Portal
• iOS Dev Center
• Stanford CS193P course site