Objective C

• Object oriented language, based on C with some elements from Smalltalk. Strongly typed.
• Most of C can still be used in Objective C.
• Used for Mac or iOS apps.
• Current version is 2.0, introduced in 2006.
• All the classes are derived from the same class, id.
• The source code is organized in header files (.h) containing class interfaces, and .m files containing the implementation.
• Instead of #include, header files are imprted with #import that automatically prevents multiple inclusions.

Class Interface

• Header file Tile.h
  

  @interface Tile : NSObject
  {
    list of class attributes
  }
  property declarations
  prototypes of class methods
  @end

Class Implementation

• Source file .Tile.m.
  

  #import .Tile.h.
  @implementation Tile
  synthesize properties
  implementation of class methods
  @end

Forward Class Declaration

• When two classes are inter-dependent.
• Interface A:
  

  #import .B.h.

• Interface B:
  

  @class A;
  @interface class B {...

• Implementation B:
  

  #import .A.h.
  #import .B.h.

Public - Protected - Private

• All class methods are public.
• Attributes are protected by default and can be declared as public/protected/private.
• All class inheritance is public.
• All methods are virtual.

Properties

• The properties are class attributes that Xcode can create set and get functions for you automatically.
• A property declaration specifies the type of attribute: readwrite, readonly, etc.
• @synthesize property; - in the implementation, creates the set/get methods for it.
• retain type of property: the attribute will not be deleted when the object itself is deleted.

Property Types

• readwrite - set/get function
• readonly - get function only
• copy - the setter function makes a copy of the object that is referenced by the property.
• assign - the setter function simply assigns the value without copying it. Used for simple values.
• retain - an additional reference to the property is made so that the referenced object is not destroyed when the object is deleted.

Class Methods

• The prototype starts with a + or a -.
• Class methods are preceded by +. Constructors are class methods and have the word alloc in the name.
• Instance methods are preceded by -.
• The return type precedes the name in parenthesis.
• Parameters are given by : (type) name and if more than one is present, they are preceded by specifiers.
• In the implementation of a method, the pointer to the target object (this in C++) is identified by self.

Calling Methods

• Calling a class method means sending the object a "message".
• Syntax for calling a method:
  [instance/class method];
• If parameters are present, add all their values and the specifiers:
  [instance/class method: arg1 spec: arg2 ...];
• Calling a method from inside a method of the same class requires the use of self:
  [self addX: 2];

Example

@implementation Tile;
- (void) setW: (int) width andH: (int) height
{ ... }
- init // type is (id) if not given
{ ... 
  return self;
}
main.m:
Tile *t = [[Tile alloc] init];
[t setW: 20 andH: 30];

Interface Builder

• Xcode provides a graphical way to build the interface.
• The Interface Builder allows you to put together the GUI elements of your app.
• This information is stored in .xib files.
• It allows you to:
• associate classes with certain interface elements;
• link attributes in the code with GUI elements displaying their values;
• establish callback functions for some events.

Model - View - Controller

• The View is a collection of interface objects, not directly visible in the code.
• The Controller is a class that links the code and the interface.
• It contains one reference to the model and references to interface objects.
• The Model is a class that handles the computations, not directly accessible from the interface.

View - Controller

• In MainMenu.xib you need to declare a generic object of class Controller.
• The View communicates to the controller through actions which are class methods in the Controller class:
  - (IBAction) myAction: (id) sender;
• The Controller communicates to the View through outlets which are attributes in the Controller class:
  IBOutletNSButton* myButton;

Example IB MainMenu.xib

Examples IB