Swift_初始化
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初始化结构体
//初始化结构体
func testInitStruct() {
//结构体 类中默认方法
struct Size {
//宽
var width = 0.0
//高
var height = 0.0
}
//默认初始化 使用的是init()构造方法
var size = Size()
//结构体自带根据成员初始化结构体的功能
size = Size(width: 10, height: 10)
print(size)
struct Point {
var x = 0.0, y = 0.0
//默认初始化
init() {
}
//通过成员初始化结构体
init(x:Double, y:Double) {
self.x = x
self.y = y
}
}
//自定义初始化
var point = Point() //调用inin()方法
point = Point(x: 10, y: 10) //调用init(x: Double, y:Double)方法
print(point)
/* print
(Size #1)(width: 10.0, height: 10.0)
(Point #1)(x: 10.0, y: 10.0)
*/
}
初始化枚举
//初始化枚举
func testInitEnum() {
enum CompassPoint:String {
case North, South, East, West
init(symbol: String) {
switch symbol {
case "North":
self = .North
case "South":
self = .South
case "East":
self = .East
default:
self = .West
}
}
}
//直接取值
var compassPoint = CompassPoint.West
print(compassPoint)
//通过原始值初始化
compassPoint = CompassPoint(rawValue: "North")!
print(compassPoint)
//通过自定义的初始化方法
compassPoint = CompassPoint(symbol: "North")
print(compassPoint)
/* print
West
North
North
*/
}
初始化类
//初始化类
func testInitClass() {
class BaseClass {
var name: String? //可选属性类型 可能为String或nil
init() {
print("Food:init()")
}
convenience init(name: String) {
self.init()
self.name = name
}
//省略外部参数
convenience init(_ subName: String) {
self.init(name: subName)
}
}
class SubClass: BaseClass {
override init() {
super.init() //实现父类的init()方法
}
}
//默认初始化
var user = SubClass()
//通过属性初始化
user = SubClass(name: "XuBaoAiChiYu")
//使用init(_ name: String)初始化
user = SubClass("XuBaoAiChiYu")
// var name = ""
// name = user.name //因为name可以为nil。此处会报错，
if let name = user.name {
print(name)
}
/* print
Food:init()
Food:init()
Food:init()
XuBaoAiChiYu
*/
}
结构体初始化失败
//结构体初始化失败
func testFailableInitStruct() {
struct Animal {
let species: String
init?(species: String) {
if species.isEmpty { return nil }
self.species = species
}
}
let someCreature = Animal(species: "Giraffe")
//someCreature is of type Animal?, not Animal
if let giraffe = someCreature {
print("\(giraffe.species)")
}
/* print
Giraffe
*/
}
枚举初始化失败
//枚举初始化失败
func testFailableInitEnum() {
enum TemperatureUnit:Character {
case kelvin = "K", celsius = "C", fahrenheit = "F"
init?(symbol: Character) {
switch symbol {
case "K":
self = .kelvin
case "C":
self = .celsius
case "F":
self = .fahrenheit
default:
return nil
}
}
}
//通过自定义方法初始化
var unit = TemperatureUnit(symbol: "F")
print(unit!) //Fahrenheit
unit = TemperatureUnit(symbol: "X")
print(unit) //nil
//通过原始值初始化
unit = TemperatureUnit(rawValue: "F")
print(unit!) //Fahrenheit
unit = TemperatureUnit(rawValue: "X")
print(unit) //nil
/*
fahrenheit
nil
fahrenheit
nil
*/
}
类初始化失败
//类初始化失败
func testFailableInitClass() {
class Product {
var name: String?
init() {}
init?(name: String) {
self.name = name
if name.isEmpty {
return nil
}
}
}
//可选链操作 当bowTie为真时 执行内部代码
if let qq = Product(name: "1045214799") {
print(qq.name!)
}
/*
Optional("1045214799")
*/
}
必须初始化
//必须初始化
func testRequiredInit() {
class SomeClass {
required init() {
//子类要调用此方法，必须继承实现
}
}
class SomeSubclass: SomeClass {
required init() {
}
init(required:String) {
super.init()
//这里调用父类的init()方法 当前类必须实现init()方法
}
}
}
使用闭包或函数设置默认属性
//使用闭包或函数设置默认属性
func testSettingDefaultPropertyValueWithClosureOrFunction() {
class SomeClass {
let someProperty: String = {
//create a default value for someProperty inside this closure
//someValue must be of the same type as SomeType
return "someValue"
}()
}
let c = SomeClass()
print(c.someProperty)
/* print
someValue
*/
}
