Swift协议Protocol介绍

目录

  • 协议(Protocol)
    • 协议中的属性
    • static、class
    • mutating
    • init
    • init、init?、init!
    • 协议的继承
    • 协议组合
    • CaseIterable
    • CustomStringConvertible

协议(Protocol) 1、协议可以用来定义方法、属性、下标的声明,协议可以被枚举、结构体、类遵守(多个协议之间用逗号隔开)
protocol Drawable {func draw()var x: Int { get set }var y: Int { get }subscript(index: Int) -> Int { get set }}

2、协议中定义方法时不能有默认参数值
3、默认情况下,协议中定义的内容必须全部都实现

协议中的属性
1、协议中定义属性时必须用var关键字
2、实现协议时属性权限要不小于协议中定义的属性权限
协议定义get、set,用var存储属性或get、set计算属性去实现
协议定义get,用任何属性都可以实现
class Person: Drawable {var x: Int = 0let y: Int = 0func draw() {print("Person draw")}subscript(index: Int) -> Int {set {}get { index }}}

class Person: Drawable {var x: Int {get { 0 }set {}}var y: Int {get { 0 }}func draw() {print("Person draw")}subscript(index: Int) -> Int {set {}get { index }}}


static、class
1、为了保证通用,协议中必须用static定义类型方法、类型属性、类型下标
protocol Drawable {static func draw()}class Person1: Drawable {class func draw() {print("Person1 draw")}}class Person2: Drawable {static func draw() {print("Person2 draw")}}


mutating
1、只有将协议中的实例方法标记为mutating
才允许结构体、枚举的具体实现修改自身内存
类在实现方法时不用加mutating,枚举、结构体才需要加mutating
protocol Drawable {mutating func draw()}class Size: Drawable {var width: Int = 0func draw() {width = 10}}static Point: Drawable {var x: Int = 0mutating func draw() {x = 10}}


init
1、协议里面还可以定义初始化器init
非final类实现时必须加上required
protocol Drawable {init(x: Int, y: Int)}class Point: Drawable {required init(x: Int, y: Int) {}}final class Size: Drawable {init(x: Int, y: Int) {}}

2、如果从协议实现的初始化器,刚好是重写了父类的指定初始化器
那么这个初始化必须同时加required、override
protocol Liveable {init(age: Int)}class Person {init(age: Int) {}}class Student: Person, Liveable {required override init(age: Int) {super.init(age: age)}}


init、init?、init!
1、协议中定义的init?、init!,可以用init、init?、init!去实现
2、协议中定义的init,可以用init、init!去实现
protocol Liveable {init()init?(age: Int)init!(no: Int)}class Person: Liveable {required init() {}//required init!() {}required init?(age: Int) {}//required init!(age: Int) {}//required init(age: Int) {}required init!(no: Int) {}//required init?(no: Int) {}//required init(no: Int) {}}


协议的继承
1、一个协议可以继承其他协议

协议组合
1、协议组合,可以包含1个类类型(最多1个)
protocol Livable {}protocol Runnable {}class Person {}//接收Person或者其子类的实例func fn0(obj: Person) {}//接收遵守Livable协议的实例func fn1(obj: Livable) {}//接收同时遵守Livable和Runnable协议的实例func fn2(obj: Livable & Runnable) {}//接收同时遵守Livable、Runnable协议,并且是Person或者其子类的实例func fn3(obj: Person & Livable & Runnable) {}

typealias RealPerson = Person & Livable & Runnablefunc fn4(obj: RealPerson) {}


CaseIterable
1、让枚举遵守CaseIterable协议,可以实现遍历枚举值
enum Season: CaseIterable {case spring, summer, autumn, winter}let seasons = Season.allCasesprint(seasons.count) // 4for season in seasons {print(season)}


CustomStringConvertible
1、遵守CustomStringConvertible协议,可以自定义实例的打印字符串
class Person: CustomStringConvertible {var age: Intvar name: Stringinit(age: Int, name: String) {self.age = ageself.name = name}var description: String {"age = \(age), name = \(name)"}}var p = Person(age: 10, name: "Jack")print(p) // age = 10, name = Jack

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