使用
\访问对象key path
struct Person {
var name:String
}
struct Book {
var title:String
var authors:[Person]
var primaryAuthor:Person {
return authors.first!
}
}
let jobs = Person(name: "Steve Jobs")
let gates = Person(name: "Bill Gates")
let book = Book(title: "Swift 入门到放弃", authors: [jobs,gates])
// 使用 \ 访问key path 也适用于计算属性
book[keyPath: \Book.title]
book[keyPath: \Book.primaryAuthor.name]
let authorKeyPath = \Book.primaryAuthor
type(of: authorKeyPath)
//如果编译器可以推断它，你可以省略类型名
let nameKeyPath = authorKeyPath.appending(path: \.name)
book[keyPath: nameKeyPath]
//也可以通过下标访问
book[keyPath: \Book.authors[0].name]
定义KVO，以及deinit掉监听
import Foundation
class Child: NSObject {
let name:String
//设置KVO 必须用 @objc dynamic 修饰
@objc dynamic var age: Int
init(name: String,age: Int) {
self.name = name
self.age = age
super.init()
}
func celebrateBirthday() {
age += 1
}
}
let mia = Child(name: "mia", age: 5)
//设置KVO
let observation = mia.observe(\.age, options: [.initial,.old]) { (child, change) in
if let oldValue = change.oldValue {
print("\(child.name)'s age is from \(oldValue) to \(child.age)")
}else {
print("\(child.name)'s age is now \(child.age)")
}
}
mia.celebrateBirthday()
//deinit掉监听
observation.invalidate()
//这里不会触发KVO
mia.celebrateBirthday()
