c#生成验证码

在做登录时通常是要带验证码，在aspx页面调用：

//切换调用

function GetSessionImg(objthis) {
    $("#txtCode").val("");
    $(objthis).attr("src", "*/load_img/ajax-loader_05.gif");//加载缩略图
    $(objthis).attr("src", "*/CheckCode.aspx?id=" + Math.random());
    $("#txtCode").focus();
}

</script>

在CheckCode.aspx后置代码：

引用命名空间：using System.Drawing;

//加载调用

protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            this.CreateCheckCodeImage(GenerateCheckCode());
        }
    }

    /// <summary>
    /// 生成4位数的验证码
    /// </summary>
    private string GenerateCheckCode()
    {
        int number;
        char code;
        string ChkCode= String.Empty;
        System.Random random = new Random();
        for (int i = 0; i < 4; i++)
        {   //随机生成
            number = random.Next();
            if (number % 2 == 0)
                code = (char)('0' + (char)(number % 10));//除以10取余数（随机数的各位如876的话就是6）00-09并强制转换
            else
                code = (char)('a' + (char)number % 26);//除以26取余数得到的结果数再以a开头往后数就是所得的值如number=28,即code=c
            ChkCode+= code.ToString();
        }
        if (checkCode.Trim().Equals("") || checkCode.Trim().Length != 4)
        {
            GenerateCheckCode();//不够四位进行生成
        }
        else
        {
            Session["User_code"] =ChkCode;//存入会话用于验证登录是否匹配
        }
        return ChkCode;
    }

/// <summary>

/// 输出验证码

/// </summary>

private void CreateCheckCodeImage(string checkCode)

{

if (checkCode == null || checkCode.Trim() == String.Empty)

{

return;

}

System.Drawing.Bitmap image = new Bitmap((int)Math.Ceiling((checkCode.Length * 12.5)), 22); //返回大于或等于指定数字的最小整数。

Graphics g = Graphics.FromImage(image);//创建图像对象

try {

Random random = new Random();

g.Clear(Color.White);

for (int i = 0; i < 25; i++)

{

int x1 = random.Next(image.Width);

int x2 = random.Next(image.Width);

int y1 = random.Next(image.Height);

int y2 = random.Next(image.Height);

g.DrawLine(new Pen(Color.GreenYellow), x1, y1, x2, y2); // 绘制一条连接由坐标对指定的两个点的线条

}

//字体

Font font = new System.Drawing.Font("Verdana", 12, (System.Drawing.FontStyle.Bold | System.Drawing.FontStyle.Italic));

//笔刷

System.Drawing.Drawing2D.LinearGradientBrush brush = new System.Drawing.Drawing2D.LinearGradientBrush(new Rectangle

(0, 0, image.Width, image.Height), Color.Blue, Color.DarkRed, 1.2f, true);

g.DrawString(checkCode, font, brush, 2, 2);

//画图片的前景噪音点

for (int i = 0; i < 80; i++)

{

int x = random.Next(image.Width);

int y = random.Next(image.Height);

image.SetPixel(x, y, Color.FromArgb(random.Next())); //一句坐标画出颜色的点

}

//画图片的边框线

g.DrawRectangle(new Pen(Color.Bisque), 0, 0, image.Width - 1, image.Height - 1);

System.IO.MemoryStream ms = new System.IO.MemoryStream();

image.Save(ms, System.Drawing.Imaging.ImageFormat.Gif);

Response.ClearContent();

Response.ContentType = "image/Gif";

Response.BinaryWrite(ms.ToArray());//将一个二进制字符串写入 HTTP 输出流

} catch (Exception ex) {

Console.Write(ex.Message);

} finally {

//关闭或释放由实现此接口的类的实例保持的文件、流和句柄等非托管资源

g.Dispose();

image.Dispose();

}