             let location = touch.location(in: self)
             if centerBtn.frame.contains(location) {
                 showPieMenu()
+                touchBeginPt = location
             }
         }
 

    var centerBtn: UIImageView? = nil
    var fullMenuBtn: UIImageView? = nil
    var listener: TouchPieMenuListener? = nil

    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)


        if let touch = touches.first {
            let pt = touch.location(in: self)
            let minMoveLength = TouchPieMenu.size / 4
            let dx = pt.x - touchBeginPt.x
            let dy = pt.y - touchBeginPt.y
            if dx * dx + dy * dy > minMoveLength * minMoveLength {
                if 0 > dx && abs(dx) > abs(dy) {
                    listener?.onBookmark()
                } else if 0 < dx && abs(dx) > abs(dy) {
                    listener?.onShare()
                }
            }
        }

