swift基础学习(06)[必要构造器,可空链式调用,错误处理,类型转换]
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 {
} }
通过设置闭包和函数来设置属性的默认值 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 } } }
3.
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 } 错误处理:用throwing函数传递错误 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 any 可以表示任何类型，包括方法类型 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")) （编辑：李大同） 【声明】本站内容均来自网络，其相关言论仅代表作者个人观点，不代表本站立场。若无意侵犯到您的权利，请及时与联系站长删除相关内容! |