Swift 中是否提供键值观察 (KVO)

在Swift中，是提供键值观察（KVO）的。KVO是一种机制，允许我们监听对象属性的变化，并在属性值发生改变时得到通知。这种机制可以用于实现数据绑定、观察模式等功能，使我们能够更方便地响应对象属性的变化。

swift
class Person: NSObject {
    @objc dynamic var name: String
    
    init(name: String) {
        self.name = name
    }
}
class Observer: NSObject {
    @objc var person: Person
    
    init(person: Person) {
        self.person = person
        super.init()
        
        person.addObserver(self, forKeyPath: #keyPath(Person.name), options: [.old, .new], context: nil)
    }
    
    deinit {
        person.removeObserver(self, forKeyPath: #keyPath(Person.name))
    }
    
    override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey : Any]?, context: UnsafeMutableRawPointer?) {
        if keyPath == #keyPath(Person.name) {
            if let newValue = change?[.newKey] as? String {
                print("Name changed to \(newValue)")
            }
        }
    }
}
let person = Person(name: "John")
let observer = Observer(person: person)
person.name = "Tom" // 输出：Name changed to Tom