GDI+ 所画的线移动时，闪烁问题，高手来

C# code

private void Frm_Report_MouseMove(object sender, MouseEventArgs e)        {            if (isClick)            {                if (count == 1)                {                    if (e.Y >= 10)                    {                        p1.Y = e.Y;                        p2.Y = e.Y;                    }                    else                    {                        p1.Y = 10;                        p2.Y = 10;                    }                    if (e.Y <= Height / 2 - 40)                    {                        p1.Y = e.Y;                        p2.Y = e.Y;                    }                    else                    {                        p1.Y = Height / 2 - 40;                        p2.Y = Height / 2 - 40;                    }                    this.Refresh();                }                if (count == 2)                {                    if (e.Y <= Height - 10)                    {                        p3.Y = e.Y;                        p4.Y = e.Y;                    }                    else                    {                        p3.Y = Height - 10;                        p4.Y = Height - 10;                    }                    if (e.Y >= Height / 2 + 40)                    {                        p3.Y = e.Y;                        p4.Y = e.Y;                    }                    else                    {                        p3.Y = Height / 2 + 40;                        p4.Y = Height / 2 + 40;                    }                    this.Refresh();                }                if (count == 3)                {                    if (e.X >= 10)                    {                        p5.X = e.X;                        p6.X = e.X;                    }                    else                    {                        p5.X = 10;                        p6.X = 10;                    }                    if (e.X <= Width / 2 - 40)                    {                        p5.X = e.X;                        p6.X = e.X;                    }                    else                    {                        p5.X = Width / 2 - 40;                        p6.X = Width / 2 - 40;                    }                    this.Refresh();                }                if (count == 4)                {                    if (e.X <= Width - 10)                    {                        p7.X = e.X;                        p8.X = e.X;                    }                    else                    {                        p7.X = Width - 10;                        p8.X = Width - 10;                    }                    if (e.X >= Width / 2 + 40)                    {                        p7.X = e.X;                        p8.X = e.X;                    }                    else                    {                        p7.X = Width / 2 + 40;                        p8.X = Width / 2 + 40;                    }                    this.Refresh();                }            }        }

效果图片暂时不懂的怎么插入，求高手指教，用GDI画了四条虚线，当移动一条虚线时，移动过程中界面闪烁的厉害，如何修改以上代码，改变界面闪烁状态

[解决办法]
初始化时 this.DoubleBuffered = true;
MouseMove中调用this.Invalidate()重绘，绘图代码写到OnPaint中