/// <summary>
        /// 獲取控制元件在客戶區的座標,相對於頂級父容器的座標
        /// </summary>
        /// <param name="c">控制元件</param>
        /// <returns>座標點</returns>
        public static Point LocationOnClient(Control c)
        {
            var retval = new Point(0, 0);
            for (; c.Parent != null
 
; c = c.Parent)
            {
                retval.Offset(c.Location);
            }
            return retval;
        }