Swift as an OOP Language

SWIFT AS AN OOP LANGUAGE
iOS Development using Swift
Ahmed Ali

TODAY TOPICS
• Classes and Structures
• Properties
• Methods
• Access Control
• Inheritance
• Initialization
• Deinitialization
• Protocols
• Transitions and View Controller Lifecycle Demo
Ahmed Ali

CLASSES AND STRUCTURES
• Both can:
• Define properties to store values
• Define methods to provide functionality
• Define subscripts
• Define initializers
• Can be extended (not subclassed, only a class can have a subclass)
• Conform to protocols
Ahmed Ali
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CLASSES AND STRUCTURES (CONT)
• Only classes can:
• Inherit from another class
• Define deinit method
• Type casted
Ahmed Ali

CLASSES AND STRUCTURES (CONT)
• Class vs Structure
• Definition Syntax:
• Classes passed by reference,
while structures are passed by
value. Structures called value
types for that reason.
• Create instance:
class SomeClass
{
}
struct SomeStruct
{
}
let someClass = SomeClass()
let someStruct = SomeStruct()
Ahmed Ali

PROPERTIES
• Properties associate values with particular type’s instances.
• Properties can be a variable or a constant
• There are two main types of properties:
• Stored Properties
• Computed Properties
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• Stored properties just store the values,
while computed properties compute
their values.
• Example of stored properties:
• No initial value for non optional?
struct Point
{
var x : Float
var y : Float
}
struct Size
{
var width : Float
var height : Float
}
PROPERTIES (CONT)
Ahmed Ali

PROPERTIES (CONT)
• Example of computed properties:
struct Rect
{
var origin = Point(x: 0, y: 0), size = Size(width: 50, height: 50)
var center : Point{
get{
return Point(x: origin.x + (size.width * 0.5), y: origin.y + (size.height * 0.5))
}
set{
origin.x = newValue.x - (size.width * 0.5)
origin.y = newValue.y - (size.height * 0.5)
}
}
}
Ahmed Ali

PROPERTIES (CONT)
• Both types of properties are accessible and modifiable in the same manner, using the dot
syntax.
• Computed properties calculated every time you access them.
//If a structure reference is defined as a constant, we will not be able to change
any of its properties
var rect = Rect()
let centerPoint = rect.center
let origin = rect.origin
//modifying their values
rect.origin.x = 50
rect.center = Point(x: 100, y: 100)
Ahmed Ali

PROPERTIES (CONT)
• Property observers:
• didSet, willSet
• Syntax:
struct Point
{
var x : Float{
didSet{
println("The value of x has been changed from (oldValue) to (x)")
}
willSet{
println("The value of x has been changed from (x) to (newValue)")
}
}
var y : Float
}
Ahmed Ali

METHODS
• Methods are used to provide functionality associated with a specific type.
• Methods can have:
• One or more parameter.
• A return value of any type.
• Can have external parameter names, for better readability.
• Definition Syntax:
class SomeClass{
func methodName(param1 : String) -> Int?
{
//countElements is a global function that returns the string length
return countElements(param1)
}
}
Ahmed Ali

METHODS (CONT)
• External parameter name, promising better readability for your method users.
• Method call without external parameter names:
let view = View()
Animator.moveView(view, Point(0, 0), Point(50, 50))
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METHODS (CONT)
• Method call with external parameter names:
let view = View()
Animator.moveView(view, fromPoint: Point(x:0, y:0), toPoint: Point(x: 50, y: 50))
Ahmed Ali

METHODS (CONT)
• Defining parameter external name:
struct Math
{
static func powerOfNumber(baseNumber: Int, toPower power: UInt) -> Int
{
var total = 0
for i in 2 ... power
{
total += (baseNumber * baseNumber)
}
return total
}
}
let value = Math.powerOfNumber(2, toPower: 3)
Ahmed Ali

METHODS (CONT)
• You can override this external name behavior if it does not make sense:
struct Math
{
static func powerOfNumber(baseNumber: Int, _ power: UInt) -> Int
{
var total = 0
for i in 2 ... power
{
total += (baseNumber * baseNumber)
}
return total
}
}
let value = Math.powerOfNumber(2, 3)
Ahmed Ali

METHODS (CONT)
• You can create static methods which can be access without the need to create an
instance.
• Example:
struct Math
{
static func add(x : Int, _ y : Int) ->Int
{
return x + y
}
}
println("5 + 6 = (Math.add(5, 6))")
Ahmed Ali

METHODS (CONT)
• For value types, you can not change any property inside any method.
• If a method will change any property value, it must be marked as a mutating method.
• Mutating method can not be called on any constant reference.
• Example:
struct SomeStruct{
var property : String
mutating func changeProperty(newValue : String)
{
property = newValue
}
}
let s = SomeStruct(property: "value")
//invalid because s is a constant
s.changeProperty("new value")
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ACCESS CONTROL
Modules vs Source Files
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ACCESS CONTROL (CONT)
• Access Levels
• Public: Accessible everywhere.
• Internal: Accessible for any source code file in defining module.
• Private: Accessible only in the same source code file.
• Internal is the default access level.
Ahmed Ali

ACCESS CONTROL (CONT)
• Syntax:
public class SomeClass
{
private var myVar = "My Var Value"
internal var myInt = 5
public func calc() -> String
{
return "(myVar) => (myInt)"
}
}
Ahmed Ali

INHERITANCE
• No universal base class that all other classes inherit from.
• Any class who has no super class, is known to be a base class.
• You can override super class methods and computed properties using the override
keyword.
• You can not override stored properties of super class, but you can observe them.
Ahmed Ali

INHERITANCE (CONT)
• Base class example:
class BaseClass
{
var computedProperty : String{
get{ return ”BaseClass property” } set{
println(newValue)
}
}
func printClassName()
{
println("BaseClass")
}
}
Ahmed Ali

INHERITANCE (CONT)
• Inheritance example:
class Subclass : BaseClass
{
}
Ahmed Ali

INHERITANCE (CONT)
• Overriding computed property example:
{
override var computedProperty : String
{
get{
return "Subclass property"
}
set{
println("Setting the property in the subclass")
}
}
}
Ahmed Ali

INHERITANCE (CONT)
• Overriding a method example:
{
override func printClassName()
{
//you can also call the original method
//which were defined in the super class
super.printClassName()
println("Subclass")
}
}
Ahmed Ali

INITIALIZATION
• Initialization is the process of creating a new instance.
• Mainly used to set non-optional properties’ values and any initial setup.
• The initialization process can not be completed while any non-optional properties still
have no value.
• Implementation is done through special methods called initializers.
Ahmed Ali

INITIALIZATION - INITIALIZERS
• An initializer is a normal method, with little different syntax.
• Initializer method is always called “init”
• You don’t write the “func” keyword before the initializer.
• Initializers always return nothing.
• Can take zero or more parameters.
• Class can have zero or more initializers.
• An initializer is required if any of your non-optional properties have no default value.
Ahmed Ali

INITIALIZATION – INITIALIZERS (CONT)
• Initializer example:
class SomeClass
{
//because we do not provide the property's initial value here
//we must provide its value in the initializer
var strProperty : String
init()
{
//If you have any property observers, they will not be called during the initial value
assignment
strProperty = "Initial value"
}
}
Ahmed Ali

• You can create custom initializer that takes one or more parameter.
• Unlike methods, all initializer’s parameters have external names by default.
• Example:
class SomeClass
{
var strProperty : String
init(strProperty: String)
{
self.strProperty = strProperty
}
}
Ahmed Ali

• Default initializer (that takes no parameters) is automatically available if and only if:
1. All your non-optional properties have default values and you did not create any
initializers at all.
• Constant property value can be modified in any initializer. However, you can not modify
super class’s constant property in a subclass initializer.
Ahmed Ali

• Create an instance the default initializer:
let someClass = SomeClass()
• Create an instance with custom initializer:
let someClass = SomeClass(strProperty: "String value")
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• In structure types, if you have not defined any initializer, a member -wise initializer is
automatically created for you.
• Example:
struct Point
{
var x : Float
var y : Float
}
Now you can create instances of the Point type using its auto-created member-wise initializer
as follows:
let point = Point(x: 15, y: 20)
Ahmed Ali

Designated Convenience
• Provides a more convenience
initializer.
• Must end up calling a designated
initializer.
• Syntax - add “conveniece” keyword
before “init”. Example:
convenience init()
{
}
• All non-optional properties’ values are
assigned before it is finished.
• For classes, it must call the super
class designated initializer if defined in
a subclass.
• Syntax - any initializer you defined
before with “init” is a designated
initializer.
Ahmed Ali
Types of initializers: designated and convenience.

class BaseClass
{
var str : String
var str2 : String
init(str : String, str2: String)
{
self.str = str
self.str2 = str2
}
convenience init(str: String)
{
self.init(str: str, str2: "String 2")
}
}
{
var substr : String
init(substr : String)
{
self.substr = substr
super.init(str:substr, str2: "none")
}
}
Ahmed Ali
Example:

DEINITIALIZATION
• Deinitlization is the process of making any final clean-up before removing a class’s
instance from the memory.
• You just need to implement a special method called deinit which takes no parameters and
returns nothing.
• Example:
deinit{
//Your clean up code goes here
}
Ahmed Ali

PROTOCOLS
• A protocol defines set of properties and methods, not their implementation.
• Any class, structure or enumeration can conform to any number of protocols.
• When a type is said to be conforming to a protocol, it means: this type provides the actual
implementation for that protocol.
• Definition syntax:
protocol SomeProtocol
{
//read and write property
var neededProperty : String {get set}
//read-only property
var anotherProperty : String {get}
func requiredMethod() -> (String, String)
}
Ahmed Ali

PROTOCOLS
• Syntax for defining a type which conforms to a protocol:
struct SomeStruct : SomeProtocol{
var neededProperty : String
var anotherProperty : String
func requiredMethod() -> (String, String) {
return ("V1", "V2")
}
}
Ahmed Ali

PROTOCOLS
• If the type is a class, and it also subclass another class, the super class name comes first
in the list.
• Example:
class Subclass : BaseClass, SomeProtocol, AnotherProtocol{
var neededProperty : String
var anotherProperty : String
func requiredMethod() -> (String, String) {
return ("V1", "V2")
}
}
Ahmed Ali

PROTOCOLS
• Protocols can be used as a type. That is, you can define any reference with the type of a
protocol instead of a concrete type.
• Example:
struct SomeStruct
{
var property : SomeProtocol
func method(param1 : AnotherProtocol)
{
}
}
Ahmed Ali

PROTOCOLS
• You can also define a reference to be any type that conforms to more than one protocol
• Example:
struct SomeStruct{
var property : protocol<SomeProtocol, AnotherProtocol>
}
Ahmed Ali

Ahmed Ali
Transitions and View Controller Lifecycle Demo

Swift as an OOP Language

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