SnappingStepper 介绍
SnappingStepper 是用 Swift 写成的一个 UIStepper 的优雅的替代品，有拇指滑块，可更加灵活地控制数值更新。
使用示例：
let stepper = SnappingStepper(frame: CGRectMake(0, 0, 100, 40))
override func viewDidLoad() {
super.viewDidLoad()
// Configure the stepper like any other UIStepper. For example:
//
// stepper.continuous = true
// stepper.autorepeat = true
// stepper.wraps = false
// stepper.minimumValue = 0
// stepper.maximumValue = 100
// stepper.stepValue = 1
stepper.font = UIFont(name: "TrebuchetMS-Bold", size: 20)
stepper.fontColor = UIColor.blackColor()
stepper.backgroundColor = UIColor.redColor()
stepper.thumbColor = UIColor.orangeColor()
stepper.addTarget(self, action: "valueChanged:", forControlEvents: .ValueChanged)
// If you don't want using the traditional `addTarget:action:` pattern you can use
// the `valueChangedBlock`
// snappingStepper.valueChangeBlock = { (value: Double) in
// println("value: \(value)")
// }
view.addSubview(stepper)
}
func valueChanged(sender: AnyObject) {
// Retrieve the value: stepper.value
}
