Author: kpark

https://developer.apple.com/library/prerelease/ios/documentation/iPhone/Conceptual/iPhoneOSProgrammingGuide/StrategiesforHandlingAppStateTransitions/StrategiesforHandlingAppStateTransitions.html

When your app is launched (either into the foreground or background), use your app delegate’s application:willFinishLaunchingWithOptions: and application:didFinishLaunchingWithOptions: methods.

At launch time, the system automatically loads your app’s main storyboard file and loads the initial view controller. For apps that support state restoration, the state restoration machinery restores your interface to its previous state between calls to the application:willFinishLaunchingWithOptions: and application:didFinishLaunchingWithOptions: methods.

 

extension String {

func toFloat() -> Float {

if let unwrappedNum = Float(self) {

return unwrappedNum

}

else {

print(“Error converting \”” + self + “\” to Float”)

return 0.0

}

}

}

 

//  Double to String with Format

var text = String.localizedStringWithFormat(“%.2f”, doubleValue)

// String to Float/Double

var floatValue = text.toFloat()

Understanding Value and Reference Types in Swift

http://alejandromp.com/blog/2014/8/30/understanding-value-and-reference-types-in-swift/

DataStructureTest.playground

// Enumeration & Class & Structure: Playground – noun: a place where people can play
// 2015.09.21 Kyoung Shin Park @ Dankook University

import Cocoa

func sayHello(personName: String = “World”) -> String {
let greeting = “Hello, ” + personName + “!”
return greeting
}
print(sayHello())
print(sayHello(“Anna”))

// Enumeration
enum Gender {
case Female
case Male
init() { // initialization
self = .Female
}
init(_ name: String)
{
switch name {
case “Female”, “여자”: self = .Female
case “Male”, “남자”: self = .Male
default: self = .Female
}
}
var description: String {
switch self {
case .Female: return “FEMALE~”
case .Male: return “MALE~”
}
}
}
var gender = Gender()
print(gender.description)
gender = Gender(“남자”)
print(gender.description)
gender = Gender.Female
gender = .Male
print(Gender.Male.description)

switch gender {
case .Female: print(“FEMALE!!”)
case .Male: print(“MALE!!”)
}

// Enum, multiple member values can appear on a single line, separated by commas
// Enum rawValue
enum Planet: Int {
case Mercury=1, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune
}
let earthID = Planet.Earth.rawValue
let somePlanet = Planet.Earth
switch somePlanet {
case .Earth:
print(“Mostly harmless”)
default:
print(“Not a safe place for humans”)
}
let aPlanet = Planet(rawValue: 7)
switch aPlanet! {
case .Earth:
print(“Mostly harmless”)
default:
print(“Not a safe place for humans”)
}
if let possiblePlanet = Planet(rawValue: 9) {
switch possiblePlanet {
case .Earth:
print(“Mostly harmless”)
default:
print(“Not a safe place for humans”)
}
} else {
print(“There isn’t a planet at position 9”)
}

// Enum associated values
enum TrainStatus {
case OnTime
case Delayed(Int)
}
var status:TrainStatus = .Delayed(5)
status = .OnTime
switch status {
case .OnTime:
print(“Train is on time”)
case .Delayed(let minutes):
print(“Train is delayed by \(minutes) minutes”)
}
// class
class Vehicle {
// stored properties
var numberOfPassengers: Int = 2
var numberOfWheels: Int = 4

// computed properties
var NumberOfWheels: Int {
get { return numberOfWheels }
set { numberOfWheels = newValue }
}
var description: String {
return “\(numberOfWheels) number of wheels”
}
}

class Bicycle: Vehicle {
override init() {
super.init()
numberOfPassengers = 1
numberOfWheels = 2
}
}

class Car: Vehicle {
// stored properties
var minVelocity: Int = 30
var accelVelocity: Int = 10
// computed properties
var speed: Int {
get {
return minVelocity + accelVelocity
}
set(newVelocity) {
accelVelocity = newVelocity – minVelocity
}
}
override init() {
super.init()
numberOfWheels = 5
}
override var description: String {
return “\(numberOfWheels) number of wheels with \(speed) speeds”
}
}
let aVehicle = Vehicle()
print(aVehicle.description)
aVehicle.numberOfWheels = 6
print(aVehicle.description)
let aBike = Bicycle()
print(aBike.description)
let aCar = Car()
print(aCar.description)
// structure
struct Frame {
var x: Int, y: Int // stored properties
var width: Int, height: Int // stored properties
var area: Int { // computed properties (getter)
return width * height
}
mutating func addWidth (width: Int) {
self.width += width // mutating modifies the value of a stored property in struct
}
}

let f = Frame(x:5, y:10, width:100, height:100)
print(f.width)
//f.width = 250 // invalid (due to let)

var g = Frame(x:5, y:10, width:100, height:100)
g.addWidth(15) // use mutating func to modify the value of a stored property in struct
print(g.width)

let h = Frame(x:5, y:10, width:100, height:100)
//h.addWidth(15) // compiler error (can’t call mutating func of struct stored in a let)
print(h.width)