SwiftUI-Day8-9 结构体

吐槽

Xcode升级，什么appdelegate都没有了，现在全是swiftUI。。。
下面的代码是playground的代码，不是swiftUI View。
参考资料：
https://www.hackingwithswift.com/100/swiftui/8
https://www.hackingwithswift.com/100/swiftui/9
时间：10 October, 2020

结果

运行快捷键：shift+command+回车
删除当前行：option+D

简单的结构体

struct Sport {
    var name: String
}
var tennis = Sport(name: "Tennis")
print(tennis.name)
tennis.name = "Lawn tennis"

计算属性 - Computed Properties

struct Sport {
    var name: String
    var isOlympicSport: Bool
	
	//下面这个属性是计算之后的属性
    var olympicStatus: String {
        if isOlympicSport {
            return "\(name) is an Olympic sport"
        } else {
            return "\(name) is not an Olympic sport"
        }
    }
}
let chessBoxing = Sport(name: "Chessboxing", isOlympicSport: false)
print(chessBoxing.olympicStatus)

属性观察

每次给amount赋值都执行didSet的内容，其实就是上面的计算过的属性

struct Progress {
    var task: String
    var amount: Int {
        didSet {
            print("\(task) is now \(amount)% complete")
        }
    }
}

var progress = Progress(task: "Loading data", amount: 0)
progress.amount = 30
progress.amount = 80
progress.amount = 100

方法 - Methods

struct City {
    var population: Int

    func collectTaxes() -> Int {
        return population * 1000
    }
}
let london = City(population: 9_000_000)
london.collectTaxes()

修改属性的方法

swift的结构体默认不让在方法里修改属性值，如果要修改需要添加mutating关键字，且实例对象是变量

struct Person {
    var name: String

    mutating func makeAnonymous() {
        name = "Anonymous"
    }
}
var person = Person(name: "Ed")
person.makeAnonymous()

字符串类型的属性和方法

let string = "Do or do not, there is no try."

print(string.count)//字符串长度
print(string.hasPrefix("Do"))//判断起始字符
print(string.uppercased())//大写
print(string.sorted())//排序

数组类型的属性和方法

var toys = ["Woody"]
print(toys.count)
toys.append("Buzz")
toys.firstIndex(of: "Buzz")
print(toys.sorted())
toys.remove(at: 0)

init - 初始化函数

不重载初始化函数

struct User {
    var username: String
}
var user = User(username: "twostraws")

重载初始化函数之后，初始化函数没有参数，所以

struct User {
    var username: String

    init() {
        username = "Anonymous"
        print("Creating a new user!")
    }
}
var user = User()
user.username = "twostraws"

self关键字 - 指向当前实例

struct Person {
    var name: String

    init(name: String) {
        print("\(name) was born!")
        self.name = name
    }
}

lazy关键字

正常情况每次都会执行FamilyTree

struct FamilyTree {
    init() {
        print("Creating family tree!")
    }
}

struct Person {
    var name: String
    var familyTree = FamilyTree()

    init(name: String) {
        self.name = name
    }
}

var ed = Person(name: "Ed")

添加lazy关键字之后，第一次调用的时候才会创建该属性

struct Person {
    var name: String
    lazy var familyTree = FamilyTree()

    init(name: String) {
        self.name = name
    }
}

var ed = Person(name: "Ed")
ed.familyTree

static关键字 - 静态属性和方法

静态属性属于结构体而不是该结构体的实例，所以调用时语法：
结构体.静态属性名

struct Student {
    static var classSize = 0
    var name: String

    init(name: String) {
        self.name = name
        Student.classSize += 1
    }
}
let ed = Student(name: "Ed")
let taylor = Student(name: "Taylor")
print(Student.classSize)

private关键字 - 私有属性

struct Person {
    private var id: String

    init(id: String) {
        self.id = id
    }

    func identify() -> String {
        return "My social security number is \(id)"
    }
}
let ed = Person(id: "12345")
ed.identify()