Swift之KVO机制

KVO（Key-Value-Observer）机制属于观察者模式。在对象属性变化时发送消息给观察者对象。

自定义观察者类：

//NSObject类实现了NSKeyValueOberving协议，只需继承NSObject类即可
class MyObserver: NSObject {
    
    //观察属性值
    override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey : Any]?, context: UnsafeMutableRawPointer?) {
        
        NSLog("\(keyPath!)--\(change![NSKeyValueChangeKey.newKey] as! String)")
    }
}

 启动KVO机制：

class ViewController: UIViewController {

    //我们想要观察的属性
    @objc dynamic var controllerStatus:NSString!
    //观察者
    var oberver: MyObserver!
    
    override func viewDidLoad() {
        super.viewDidLoad()
        //创建观察者对象
        self.oberver = MyObserver()
        //开始观察controllerStatus属性变化
        self.addObserver(oberver, forKeyPath: "controllerStatus", options: [NSKeyValueObservingOptions.new,NSKeyValueObservingOptions.old], context: nil)
        
        self.controllerStatus = "viewDidLoad"
        
    }
    
    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)
        self.controllerStatus = "viewDidAppear"
    }

    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)
        self.controllerStatus = "viewWillAppear"
    }
    
    override func viewDidLayoutSubviews() {
        super.viewDidLayoutSubviews()
        self.controllerStatus = "viewDidLayoutSubviews"
    }
    
    override func viewWillDisappear(_ animated: Bool) {
        super.viewWillDisappear(animated)
        self.controllerStatus = "viewWillDisappear"
    }
    
    override func viewDidDisappear(_ animated: Bool) {
        super.viewDidDisappear(animated)
        self.controllerStatus = "viewDidDisappear"
    }

}