Swift KVC/KVO

Swift支持KVC/KVO的条件

属性所在的类、监听器最终继承自NSObject

@objc dynamic修饰对应的属性

class Observer : NSObject {
    
    override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey : Any]?, context: UnsafeMutableRawPointer?) {
        print("observerValue",change?[.newKey] as Any)
    }
}

class Person : NSObject {
    
    @objc dynamic var age: Int = 0
    var observer : Observer = Observer()
    override init() {
        super.init()
        self.addObserver(observer, forKeyPath: "age", options: .new, context: nil)
    }
    deinit {
        
        self.removeObserver(observer, forKeyPath: "age")
    }
}

var p : Person = Person()
p.age = 20
p.setValue(25, forKey: "age")

打印结果

observerValue Optional(20)
observerValue Optional(25)

block方式的KVO

class Person : NSObject {
    
    @objc dynamic var age:Int = 0
    var observation: NSKeyValueObservation?
    override init() {
        super.init()
        observation = observe(\Person.age, options: .new, changeHandler: { Person, Change in
            print(Change.newValue as Any)
        })
    }
}

这个与第一个的写法不同的是，不用单独在创建一个observe类，而且是以block的方式实现的