（一）UI 篇之 Button

let btn1 = UIButton.buttonWithType(.System) as UIButton
btn1.backgroundColor = UIColor.redColor()
btn1.setTitle("Button1", forState: UIControlState.Normal)
btn1.frame = CGRect(x: 10, y: 80, width: 300, height: 30)
btn1.tag = 100
self.view.addSubview(btn1)
        
let btn2 = UIButton.buttonWithType(.System) as UIButton
btn2.backgroundColor = UIColor.blueColor()
btn2.setTitle("Button2", forState: UIControlState.Normal)
btn2.setTitleColor(UIColor.redColor(), forState: .Normal)
// set round corner
btn2.layer.cornerRadius = 10.0
btn2.frame = CGRect(x: 10, y: 120, width: 300, height: 30)
btn2.tag = 101
self.view.addSubview(btn2)
        
let btn3 = UIButton.buttonWithType(.System) as UIButton
btn3.setTitle("Button3", forState: UIControlState.Normal)
btn3.layer.cornerRadius = 10.0
// set border
btn3.layer.borderWidth = 1
btn3.layer.borderColor = UIColor.blueColor().CGColor
btn3.frame = CGRect(x: 10, y: 160, width: 300, height: 30)
btn3.tag = 102
self.view.addSubview(btn3)
        
// set listeners
// Selector is a struct it convert a string to C pointer
btn1.addTarget(self, action: Selector("onBtnClick:"), forControlEvents: UIControlEvents.TouchUpInside)
btn2.addTarget(self, action: Selector("onBtnClick:"), forControlEvents: UIControlEvents.TouchUpInside)
btn3.addTarget(self, action: Selector("onBtnClick:"), forControlEvents: UIControlEvents.TouchUpInside)

func onBtnClick(btn:UIButton){
    var msg = ""
    
    switch btn.tag{
    case 100:
        msg = "you clicked button1"
    case 101:
        msg = "you clicked button2"
    case 102:
        msg = "you clicked button3"
    default:
        println("default")
    }
    
    // In IOS8 the UIAlertView is deprecated
    // now we use UIAlertController
    var alert = UIAlertController(title: "Alert", message: msg, preferredStyle: UIAlertControllerStyle.Alert)
    var ok = UIAlertAction(title: "OK", style: UIAlertActionStyle.Default, handler:{
        (action) in
            println("you clicked ok")
        })
    alert.addAction(ok)
    self.presentViewController(alert, animated: true)
}