基本类型的监听 包括String、Int、数组等等
Person为被监听的对象，name被监听的属性
class Person: NSObject {
@objc dynamic var name: String
init(name: String) {
self.name = name
}
}
KVO是基于KVC(Key-Value Coding)以及动态派发技术实现，所以class要继承NSObject，需要监听属性的对象要标记为@objc dynamic
ViewController为监听者，需要监听Person中name的变化
class ViewController: UIViewController {
var person: Person!
var observation: NSKeyValueObservation?
override func viewDidLoad() {
super.viewDidLoad()
person = Person(name: "name")
observation = person.observe(\Person.name, options: [.new,.old], changeHandler: { (p, change) in
if let name = change.oldValue {
print("旧名字：" + name)
}
if let name = change.newValue {
print("新名字：" + name)
}
})
}
@IBAction func tap(_ sender: UIButton) {
person.name = "shao"
}
}
// 打印结果
旧名字：name
新名字：shao
Enum类型
需要做个转换
class ViewModel: NSObject {
enum AnEnumType : String {
case enumA = "A"
case enumB = "B"
}
// 监听类型为
@objc dynamic private(set) var anEnumRaw : String = ""
var anEnumType : AnEnumType? {
didSet {
anEnumRaw = anEnumType?.rawValue ?? "none"
}
}
}
