@IBOutlet weak var annularSlider: BSAnnularSlider! {
        didSet {
            annularSlider.backgroundColor = UIColor.clearColor()
            annularSlider.thumbImage = UIImage(named: "thumb")

            //optional
            //if the thumb image is too small, you can set this to exten responds area
            annularSlider.extendRespondsDistance = 10
            //cannot set more than maxRadius
            annularSlider.radius = 200

            annularSlider.addTarget(self, action: #selector(ViewController.respondsToSliderValueChanged(_:)), forControlEvents: UIControlEvents.ValueChanged)
            annularSlider.addTarget(self, action: #selector(ViewController.respondsToSliderTouchUp(_:)), forControlEvents: UIControlEvents.TouchUpInside)

        }
    }
@end