How to grab and save an image from a default UIButton

GrabSaveImageUIButton

    override func viewDidLoad() {
        let fileName = "infoLight.png"
        let b = UIButton.buttonWithType(UIButtonType.InfoLight) as! UIButton
        let img = b.imageForState(.Normal)
        
        let paths = NSSearchPathForDirectoriesInDomains(.DocumentDirectory, .UserDomainMask, true)
        let dir = (paths[0] as! String)+"/"+fileName

        UIImagePNGRepresentation(img).writeToFile(dir, atomically: true)
        
        println(dir)
    }