无标题栏窗口的移动

Point  oldpoint =new Point();

private void Form1_MouseMove(object sender, MouseEventArgs e)
        {
            if (e.Button == MouseButtons.Left)
            {
                Point newpoint = Cursor.Position;//鼠标相对于屏幕的坐标位置
                newpoint.Offset(oldpoint.X, oldpoint.Y);
                this.Location = newpoint;
            }
        }
      
        private void Form1_MouseDown(object sender, MouseEventArgs e)
        {
            oldpoint = new Point(-e.X, -e.Y);//鼠标第一次点击时相对于窗口的坐标，加负号，
        }