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2. Cocoa and MVC in iOS

3. What Is Cocoa?
 Cocoa is an application environment for both the OS X
operating system and iOS, the operating system used on
Multi-Touch devices such as iPhone, iPad, and iPod touch.
 It consists of a suite of object-oriented software libraries, a
runtime system, and an integrated development environment.

4. The Cocoa Environment
 Cocoa is a set of object-oriented frameworks that provides a
runtime environment for applications running in OS X and iOS.
 Cocoa is the preeminent application environment for OS X
and the only application environment for iOS.

5. Cont..
 On any system there are many Cocoa frameworks, and Apple
and third-party vendors are releasing more frameworks all the
time.
 In OS X: Foundation and AppKit
 In iOS: Foundation and UIKit
 The Foundation, AppKit, and UIKit frameworks are essential
to Cocoa application development, and all other frameworks
are secondary and elective.

6. Cont..
 You cannot develop a Cocoa application for OS X unless you
use the classes of the AppKit.
 you cannot develop a Cocoa application for iOS unless you
use the classes of UIKit.

7. How Cocoa Fits into iOS

8. The Development Environment
 Cocoa provides the infrastructure for event-driven behavior
and for
 management of applications, windows, and (in the case of OS
X) workspaces. In most cases, you won’t
 have to handle events directly or send any drawing
commands to a rendering library.

9. Properties, Protocols and
Categories in Cocoa

10. Properties
 properties feature provides a simple way to declare and
implement an object’s accessor methods.
 We access an object’s properties in the sense of its
attributes and relationships through a pair of accessor
(getter/setter) methods.
 By using accessor methods,

11. properties address these issues by
providing the following features:
 The property declaration provides a clear, explicit specification
of how the accessor methods behave.
 The compiler can synthesize accessor methods for you,
according to the specification you provide in the declaration.
 Properties are represented syntactically as identifiers and are
scoped, so the compiler can detect use of undeclared
properties.

12.  Property Declaration
@property (attributes) type name;
 Syantax
 @property(nonautomatic,
retain)UITextField *text;

13. Property Declaration Attributes
 You can decorate a property with attributes by using the form
@property(attribute [, attribute2, ...]).
 Like methods, properties are scoped to their enclosing
interface declaration.
 For property declarations that use a comma-delimited list of
variable names, the property attributes apply to all of the
named properties.

14. Accessor Method Names
 The default names for the getter and setter methods
associated with a property are propertyName and
setPropertyName:
 getter=getterName
 setter=setterName

15. Writability
 Readwrite-default property
Indicates that the property should be treated as read/write. This
attribute is the default.
 Readonly:
----Indicates that the property is read-only.

16. Setter Semantics
 Strong
 Weak
 Copy
 assign
 retain

17. Atomicity
 You can use this attribute to specify that accessor methods
are not atomic. (There is no keyword to denote atomic.)
nonatomic
Ex..
@property (nonatomic, weak) IBOutlet NSButton *myButton;

18. Property Implementation
 You can use the @synthesize and @dynamic directives in
@implementation blocks to trigger specific compiler actions.
Ex..
 @synthesize value;
 @synthesize firstName, lastName, age=yearsOld;

19. Categories
 A category allows you to add methods to an existing class—
even to one for which you do not have the source.
 Categories are a powerful feature that allows you to extend
the functionality of existing classes without subclassing.
 Using categories, you can also distribute the implementation
of your own classes among several files.

20. Adding Methods to Classes
 You can add methods to a class by declaring them in an
interface file under a category name and defining them in
an implementation file under the same name.
 The category name indicates that the methods are
additions to a class declared elsewhere, not a new class.
 You cannot, however, use a category to add additional
instance variables to a class.

21. Conti..
 The declaration of a category interface looks very much
like a class interface declaration—except the category
name is listed within parentheses after the class name and
the superclass isn’t mentioned.
#import "ClassName.h“
@interface ClassName ( CategoryName )
// method declarations
@end

22. Protocols
 Protocols declare methods that can be implemented by
any class.
 Protocols are useful in at least three situations:
1.To declare methods that others are expected to
implement.
2. To declare the interface to an object while concealing
its class.
3. To capture similarities among classes that
are not hierarchically related.

23. Types of Protocol
- Formal
- Informal
Formal protocol
- The Objective-C language provides a way to formally
declare a list of methods (including declared properties) as
a protocol.
- Formal protocols are supported by the language and the
runtime system.
- For example, the compiler can check for types based on
protocols, and objects can introspect at runtime to report
whether or not they conform to a protocol.

24. Declaring
You declare formal protocols with the @protocol
directive:
@protocol ProtocolName
//method declarations
@end
Ex.
@protocol MyXMLSupport
- initFromXMLRepresentation:(NSXMLElement
*)XMLElement;
(NSXMLElement *)XMLRepresentation; @end

25. Informal Protocols
 informal protocol by grouping the methods in a category
declaration:
 Ex.
interface NSObject ( MyXMLSupport )
-initFromXMLRepresentation: (NSXMLElement
*)XMLElement;
-- (NSXMLElement *)XMLRepresentation;
@end

26. Important Cocoa classes
◦ There are several important Cocoa classes that you will
often use in your iPhone application.
NSObject
◦ This is the base class of most Cocoa classes. An object is
not considered a Cocoa object if it is not an instance
of NSObject or any class that inherits from NSObject.
◦ This class defines the runtime methods required for
allocating and deallocating objects.

27. Cont..
NSString
 This is the main class representing strings in Cocoa.
 Using this class, you can store an arbitrary text.
 However, once you store a value in an object of this type, you
cannot change it.
 This kind of class is referred to as immutableTo be able to
change a string’s value you need the mutable string class
NSMutableString.
 You can create a constant string using the “@” sign.

28. Cont..
NSArray
 Instances of this class represents Cocoa array objects. The
mutable version of this class is NSMutableArray.
NSSet
 Instances of this class represents Cocoa set objects.
 The mutable version is NSMutableSet.

29. Understanding MVC architecture

30. Model-View-Controller
 The Model-View-Controller (MVC) design pattern assigns
objects in an application one of three roles: model, view, or
controller.
 The pattern defines not only the roles objects play in the
application, it defines the way objects communicate with each
other.
 Each of the three types of objects is separated from the
others by abstract boundaries and communicates with
objects of the other types across those boundaries..

31. Cont..
 MVC is central to a good design for a Cocoa application.
 The benefits of adopting this pattern are numerous.
 Many objects in these applications tend to be more
reusable, and their interfaces tend to be better defined.
 Applications having an MVC design are also more easily
extensible than other applications.
 Many Cocoa technologies and architectures are based on
MVC and require that your custom objects play one of the
MVC roles.

32. Architecture of MVC

33. MVC

34. MVC

35. Model Objects
 What your application is (but not how it is displayed) .
 Model objects encapsulate the data specific to an application
and define the logic and computation that manipulate and
process that data.
 a model object should have no explicit connection to the view
objects that present its data and allow users to edit that
data—it should not be concerned with user-interface and
presentation issues.

36. View Objects
 A view object is an object in an application that users can
see.
 A view object knows how to draw itself and can respond to
user actions.
 A major purpose of view objects is to display data from the
application’s model objects and to enable the editing of that
data.
 Despite this, view objects are typically decoupled from model
objects in an MVC application.

37. Controller Objects
 How your Model is presented to the user (UI logic).
 A controller object acts as an intermediary between one or
more of an application’s view objects and one or more of its
model objects.
 Controller objects are thus a conduit through which view
objects learn about changes in model objects and vice versa.
 Controller objects can also perform setup and coordinating
tasks for an application and manage the life cycles of other
objects.

38. Cont..
 Communication:
 A controller object interprets user actions made in view
objects and communicates new or changed data to the
model layer.
 When model objects change, a controller object
communicates that new model data to the view objects so
that they can display it.

39. Thank You