PROPERTIES
最后更新于:2022-04-01 04:44:36
## PROPERTIES
结构体和类(统称为 types)可以拥有自己的变量和常量(统称为 properties)。types 也可拥有方法来处理 properties:
~~~
struct Person {
var clothes: String
var shoes: String
func describe() {
print("I like wearing \(clothes) with \(shoes)")
}
}
let taylor = Person(clothes: "T-shirts", shoes: "sneakers")
let other = Person(clothes: "short skirts", shoes: "high heels")
taylor.describe() //"I like wearing T-shirts with sneakers"
other.describe() //"I like wearing short skirts with high heels"
//调用方法时,不同的对象使用相应的值
~~~
### Property observers
Swift 提供了两个观察者方法,willSet 和 didSet,分别会在属性的值将要改变以及改变后触发(常用于用户界面的更新):
~~~
struct Person {
var clothes: String {
willSet {
updateUI("I'm changing from \(clothes) to \(newValue)")
}
didSet {
updateUI("I just changed from \(oldValue) to \(clothes)")
}
}
}
func updateUI(msg: String) {
print(msg)
}
var taylor = Person(clothes: "T-shirts")
taylor.clothes = "short skirts" //值改变,将会调用观察者方法
~~~
### Computed properties
Computed properties 其实就是自己重写属性的 get/set 方法:
~~~
struct Person {
var age: Int
var ageInDogYears: Int {
get {
return age * 7
}
}
}
var fan = Person(age: 25)
print(fan.ageInDogYears) //输出:25 * 7
~~~
### Static properties and methods
静态属性和方法属于 type(class\struct),而不属于类的实例,这可以更好的组织一个共享的储存数据。通过 static 关键字声明一个静态变量:
~~~
struct TaylorFan {
static var favoriteSong = "Shake it Off"
var name: String
var age: Int
}
let fan = TaylorFan(name: "James", age: 25)
print(TaylorFan.favoriteSong)
//每个 TaylorFan 类型的对象都会有自己的名字和年龄,但他们都有共同喜欢的歌曲:"Shake it Off"
~~~
因为静态属性和方法存在于 类 中,所以静态方法是无法访问非静态属性的。