1.在类的构造器前添加required修饰符表明所有该类的子类都必须实现该构造器
必要构造器实现的代码
class SomeClass {
required init(){
}
}
子类重写父类的必要构造器方法实现的代码不需要添加override
class SomeSubClass: SomeClass {
}
}
struct Checkerboard {
let boardColors: [Bool] = {
var temporaryBoard = [Bool]()
var isBlack = false
for i in 1...10 {
for j in 1...10 {
temporaryBoard.append(isBlack)
isBlack = !isBlack
}
isBlack = !isBlack
}
return temporaryBoard
}()
func squareIsBlackAtRow(row: Int,column: Int) -> Bool {
return boardColors[(row * 10) + column]
}
}
let board = Checkerboard()
print(board.squareIsBlackAtRow(0,column: 1))
2. 可空链式调用是一种可以请求和调用属性、方法及下标的过程，它的可控件体现于请求或调用的目标当前可能为空,如果可空的目标有值，那么调用就会成功,如果选择的目标为空,那么这种调用将返回空,多个连续调用可以背链接在一起形成一个调用链,如果其中任何一个节点为空将导致整个链调用失败
class Person {
var residence:Residence?
}
class Residence {
var rooms = [Room]()
var numberOfRooms: Int {
return rooms.count
}
subscript(i: Int) -> Room {
get {
return rooms[i]
}
set {
rooms[i] = newValue
} }
func printNumberOfRooms() {
print("The number of rooms is \(numberOfRooms)")
}
var address: Address?
}
class Room {
let name: String
init(name: String) { self.name = name }
}
class Address {
var buildingName: String?
var buildingNumber: String?
var street: String?
func buildingIdentifier() -> String? {
if buildingName != nil {
return buildingName
} else if buildingNumber != nil {
return buildingNumber
} else {
return nil
} }
}
错误处理:是响应错误以及从错误中恢复的过程。swift提供了在运行对可恢复错误抛出,捕获传送和操作的高级支持
表示并抛出错误:在Swift中,错误用遵循 ErrorType 协议类型的值来表示
enum VendingMachineError:ErrorType {
case InvalidSelection//选择无效
case InsufficientFunds(coinsNeed:Int)//金额不足
case OutOfStock//缺货
}
用do-catch处理错误
4.
类型转换
class MediaItem {
var name: String
init(name:String){
self.name = name
}
}
class Movie:MediaItem {
var director:String
init(name:String,director:String){
self.director = director
super.init(name: name)
}
}
class Song: MediaItem {
var artist:String
init(name:String,artist:String){
self.artist = artist
super.init(name: name)
}
}
给一个数组常量
let library = [ Movie(name: "Casablanca",director: "Michael Curtiz"),
Song(name: "Blue Suede Shoes",artist: "Elvis Presley"),
Movie(name: "Citizen Kane",director: "Orson Welles"),
Song(name: "The One And Only",artist: "Chesney Hawkes"),
Song(name: "Never Gonna Give You Up",artist: "Rick Astley")
]
//检查类型:用类型检查操作符( is )来检查一个实例是否属于特定子类型
var movieCount = 0
var songCount = 0
for item in library {
if item is Movie {
++movieCount
} else if item is Song {
++songCount
}
}
print(movieCount,songCount)
向下转型:某类型的一个常量或变量可能在幕后实际上属于一个子类。当确定是这种情况时,你可以尝试向下转到它的子类型,用类型转换操作符(as? 或 as!)
for item in library {
if let movie = item as? Movie {
print("Movie:'\(movie.name)',dir.\(movie.director)")
} else if let song = item as? Song {
print("Song:'\(song.name)',by \(song.artist)")
}
}
any 和anyobject的类型转换
swift为不确定类型提供了特殊类型别名
anyobject 可以代表任何class类型的实例
let someObjects: [AnyObject] = [
Movie(name: "2001: A Space Odyssey",director: "Stanley Kubrick"),
Movie(name: "Moon",director: "Duncan Jones"),
Movie(name: "Alien",director: "Ridley Scott")
]
for object in someObjects {
let movie = object as! Movie
print("Movie: '\(movie.name)',dir. \(movie.director)")
}
any类型
var things = [Any]()
things.append(0)
things.append(0.0)
things.append(42)
things.append(3.1415126)
things.append("hello")
things.append(Movie(name:"lihuan",director: "hello"))
