var sheet = UIActionSheet(title: nil, delegate: self, cancelButtonTitle: nil, destructiveButtonTitle: nil)
sheet.addButton(withTitle: "按键学习")
sheet.addButton(withTitle: "扫码学习")
sheet.addButton(withTitle: "取消")
sheet.cancelButtonIndex = 2
sheet.show(in: self.view)
实现UIActionSheetDelegate
func actionSheet(_ actionSheet: UIActionSheet, clickedButtonAt buttonIndex: Int) {
print(buttonIndex)
}