随机生成验证码

 

        /// <summary>
        /// 随机生成验证码
        /// </summary>
         protected void CreateSecCode()
        {
            //创建一个包含随机内容的验证码文本   
             System.Random rand = new Random();
            int len = rand.Next(4, 6);//返回一个大于等于4，小于6的整型随机数
            char[] chars = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ".ToCharArray();//定义一个char数组

            //用于追加字符串，效率比string更高效
            System.Text.StringBuilder myStr = new System.Text.StringBuilder();

            for (int iCount = 0; iCount < len; iCount++)
            {
                myStr.Append(chars[rand.Next(chars.Length)]);
            }
            string text = myStr.ToString();//生成的随机内容

            // 保存验证码到 session 中以便其他模块使用   
            this.Session["checkcode"] = text;

            Size ImageSize = Size.Empty;//用于存储验证码图片大小
            Font myFont = new Font("MS Sans Serif", 20);

            // 计算验证码图片大小   
            using (Bitmap bmp = new Bitmap(10, 10))
            {
                using (Graphics g = Graphics.FromImage(bmp))
                {
                    SizeF size = g.MeasureString(text, myFont, 10000);//获取特定字体样式的文本大小
                    ImageSize.Width = (int)size.Width + 8;
                    ImageSize.Height = (int)size.Height + 8;
                }
            }

            // 创建验证码图片   
            using (Bitmap bmp = new Bitmap(ImageSize.Width, ImageSize.Height))
            {
                // 绘制验证码文本   
                using (Graphics g = Graphics.FromImage(bmp))
                {
                    g.Clear(Color.White);
                    using (StringFormat f = new StringFormat())
                    {
                        f.Alignment = StringAlignment.Near;
                        f.LineAlignment = StringAlignment.Center;
                        f.FormatFlags = StringFormatFlags.NoWrap;
                        g.DrawString(
                            text,
                            myFont,
                            Brushes.Red,
                            new RectangleF(
                            0,
                            0,
                            ImageSize.Width,
                            ImageSize.Height),
                            f);
                    }//using   
                }//using   

                // 制造噪声 杂点面积占图片面积的 8%   
                int num = ImageSize.Width * ImageSize.Height * 8 / 100;

                for (int iCount = 0; iCount < num; iCount++)
                {
                    // 在随机的位置使用随机的颜色设置图片的像素   
                    int x = rand.Next(ImageSize.Width);
                    int y = rand.Next(ImageSize.Height);
                    int r = rand.Next(255);
                    int g = rand.Next(255);
                    int b = rand.Next(255);
                    Color c = Color.FromArgb(r, g, b);
                    bmp.SetPixel(x, y, c);
                }//for                

                // 输出图片   
                System.IO.MemoryStream ms = new System.IO.MemoryStream();
                bmp.Save(ms, System.Drawing.Imaging.ImageFormat.Png);
                this.Response.ContentType = "image/png";
                ms.WriteTo(this.Response.OutputStream);
                ms.Close();
            }//using

            myFont.Dispose();
        }