swift中KVO简单使用，监听属性值改变

直接上代码

import UIKitclass ViewController: UIViewController {    let per = Person()    override func viewDidLoad() {        super.viewDidLoad()        /// 添加观察者        per.addObserver(self, forKeyPath: "name", options: [.new,.old], context: nil)    }    // 点击屏幕通过kvc给Person里面的name赋值    override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {        let num = Int(arc4random()%10000) + 1        per.setValue("\(num)", forKey: "name")    }    /// KVO监听属性    ///    /// - Parameters:    ///   - keyPath: 被监听的属性名    ///   - object:    ///   - change:    ///   - context:    override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey : Any]?, context: UnsafeMutableRawPointer?) {        print(keyPath ?? "")        print("完成回调 -- \(String(describing: per.value(forKey: keyPath!)))")    }}

import UIKitclass Person: NSObject {    var name:String?}