void formsample_mousewheel(object sender, MouseEventArgs e)

         {

             //获取光标位置

             Point mousepoint = new Point(e.X, e.Y);

             //换算成相对本窗体的位置

             mousepoint.Offset(this.Location.X, this.Location.Y);

             //判断是否在panel内

             if (pl_message.RectangleToScreen(pl_message.DisplayRectangle).Contains(mousepoint))

             {

                 //滚动

                 pl_message.AutoScrollPosition = new Point(, pl_message.VerticalScroll.Value - e.Delta);

             }

         }

  this.MouseWheel += formsample_mousewheel;