C# winform 拖拽效果

        //是否在拖拽
        bool isDrag = false;
        //鼠标相对于button控件左上角的坐标
        Point contextbtnPoint = Point.Empty;
        private void button1_MouseDown(object sender, MouseEventArgs e)
        {
            isDrag = true;
            if (e.Button == MouseButtons.Left)
            {
                contextbtnPoint = button1.PointToClient(Control.MousePosition);  //鼠标相对于button左上角的坐标
            }
        }
        private void button1_MouseMove(object sender, MouseEventArgs e)
        {
            if (isDrag)
            {
                Point formPoint = this.PointToClient(Control.MousePosition);//鼠标相对于窗体左上角的坐标
                int x = formPoint.X - contextbtnPoint.X;
                int y = formPoint.Y - contextbtnPoint.Y;
                button1.Location = new Point(x, y);
            }
        }
        private void button1_MouseUp(object sender, MouseEventArgs e)
        {
            if (isDrag)
            {
                isDrag = false;
            }
        }