C# 中自定义控件pictureBox 自定义方法

Question

自定义的方法怎么才能在父窗口中调用。由于OnPaint函数总会被自动调用，需要将如下方法的功能重新写一个方法。但是
不知道怎么调用啊～～～
        protected override void OnPaint(PaintEventArgs e)
        {
            if (size)
            {
                Pen pp = new Pen(Color.Black, 4);
                e.Graphics.DrawRectangle(pp, e.ClipRectangle.X + 1,
                    e.ClipRectangle.Y + 1, e.ClipRectangle.X + e.ClipRectangle.Width - 2,
                    e.ClipRectangle.Y + e.ClipRectangle.Height - 2);                P_X = e.ClipRectangle.X + 1;
                P_Y = e.ClipRectangle.Y + 1;
                PWidth = e.ClipRectangle.X + e.ClipRectangle.Width - 2;
                PHeight = e.ClipRectangle.Y + e.ClipRectangle.Height - 2;
            }
            else
            {
                Pen pp = new Pen(Color.Black, 4);
                e.Graphics.DrawRectangle(pp, P_X,
                    P_Y, PWidth, PHeight
                    );
            }
            size = false;            if (Alarm)
            {
                timer1.Enabled = true;
                timer1.Interval = 500;
                flag = false;
            }
            else
            {
                timer1.Enabled = false;
                if (!flag)
                {
                    Pen pen = new Pen(Color.Black, 4);
                    e.Graphics.DrawRectangle(pen, e.ClipRectangle.X + 1,
                        e.ClipRectangle.Y + 1, e.ClipRectangle.X + e.ClipRectangle.Width - 2,
                        e.ClipRectangle.Y + e.ClipRectangle.Height - 2); ;
                }
            }
            base.OnPaint(e);
        }