尽管swift作为一门新语言，但还保留了许多ＯＣ的机制，使得swift和OC更好的融合在一起。如果没有ＯＣ基础的先ＧＯＯＧＬＥ一下。

如：ＫＶＯ，ＤＥＬＥＧＡＴＥ，ＮＯＴＩＦＩＣＡＴＩＯＮ。

详见ＤＥＭＯ。

import Foundation

@objc   // 需要打开objc标识，否则@optional编译出错

protocol kvoDemoDelegate {
func willDoSomething()
@optional  func didDoSomething()  //可选实现,
}

let ntfname = "test_notification"

class kvoDemo : NSObject //不写NSObject默认就是从NSObject来的
{
    var delegate: kvoDemoDelegate!
    
    var presult : Double = 0.0
    
    var result : Double {
        get{
            return presult;
        }
    
        set{
          self.presult = newValue
        }
    }
    
    init()
    {
        
    }
    
    func doSomething()
    {
        if let yet = self.delegate?
        {
            delegate!.willDoSomething()
        }
        
        for _ in 1..5
        {
            println("i‘m doing now,don‘t touch me,please.")
        }
        
        if let yet = self.delegate?
        {
            delegate!.didDoSomething!()
        }
    }
    
    func notificationPost()
    {
        let ntf = NSNotificationCenter.defaultCenter()
        ntf.postNotificationName(ntfname, object :nil, userInfo:nil)
    }
    
    deinit
    {
        
    }
}

class ViewController: UIViewController,kvoDemoDelegate {
    
    //KVO
    override func observeValueForKeyPath(keyPath: String?, ofObject: AnyObject?, change: NSDictionary?, context: CMutableVoidPointer)
    {
        if keyPath == "result"
        {
            var newvalue : AnyObject? = change?.objectForKey("new");
            println("the new value is \(newvalue)")
        }
    }
    
    //delegate
    func willDoSomething()
    {
        println("i will do it.")
    }
    
    func didDoSomething()
    {
        println("i had do it.")
    }
    
    //notification
    func onRecviceNotification(notification:NSNotification)
    {
        println("Recevice notification \(notification)")
    }

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
        
        var kvo = kvoDemo()
        kvo.addObserver(self, forKeyPath: "result", options: NSKeyValueObservingOptions.New | NSKeyValueObservingOptions.Old, context: nil)

        kvo.result = 280.0
        
        kvo.removeObserver(self,forKeyPath:"result",context: nil)
        
        kvo.delegate = self
        kvo.doSomething()
        
        let ntf = NSNotificationCenter.defaultCenter()
        ntf.addObserver(self, selector:"onRecviceNotification:", name :ntfname, object : nil)
        kvo.notificationPost()
        ntf.removeObserver(self)
    }
}

the new value is 280
i will do it.
i‘m doing now,don‘t touch me,please.
i‘m doing now,don‘t touch me,please.
i‘m doing now,don‘t touch me,please.
i‘m doing now,don‘t touch me,please.
i had do it.
Recevice notification NSConcreteNotification 0x10be60930 {name = test_notification}