c#遍历控件绘制

       private void dropShadow(object sender, PaintEventArgs e)
        {
            Panel panel = (Panel)sender;
            Color[] shadow = new Color[3];
            shadow[0] = Color.FromArgb(181, 181, 181);
            shadow[1] = Color.FromArgb(195, 195, 195);
            shadow[2] = Color.FromArgb(211, 211, 211);
            Pen pen = new Pen(shadow[0]);
            LogUtil.writeLog("dropShadow call:");
            using (pen)
            {
                foreach (Control p in panel.Controls.OfType())
                {
                    LogUtil.writeLog("绘制控件:"+p.GetType());
                    Point pt = p.Location;
                    pt.Y += p.Height;
                    for (var sp = 0; sp < 3; sp++)
                    {
                        pen.Color = shadow[sp];
                        e.Graphics.DrawLine(pen, pt.X, pt.Y, pt.X + p.Width - 1, pt.Y);
                        pt.Y++;
                    }
                }
            }
        }
        private void Form1_Load(object sender, EventArgs e)
        {
            panel_keyboard_head.Paint += dropShadow;

然而并没有达到什么效果