asp.Net 一些常用的方法和类(2)

        Random rd = new Random(); 
        for (int i = 0; i < num; i++) 
        { 
            code += source[rd.Next(0, source.Length)]; 
        } 
        Session["ValidateCode"] = code;//将字符串保存到Session中，以便需要时进行验证   
        return code; 
 
    } 
 
 
    #region    验证码 
 
    /// <summary> 
    /// 生成验证码 
    /// </summary> 
    /// <param name="checkCode"></param> 
    private void GetCheckCodeImage(string checkCode) 
    { 
        if (checkCode == null || checkCode.Trim() == String.Empty) return; 
 
        System.Drawing.Bitmap image = new System.Drawing.Bitmap((int)Math.Ceiling((checkCode.Length * 12.5)),25); 
        Graphics g = Graphics.FromImage(image); 
        try 
        { 
            Random random = new Random();     //生成随机生成器  
            g.Clear(Color.White);            //清空图片背景色 www.2cto.com
            for (int i = 0; i < 5; i++)     //画图片的背景噪音线 
            { 
                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.Silver), x1, y1, x2, y2); 
            } 
            Font font = new System.Drawing.Font("Arial", 12, (System.Drawing.FontStyle.Bold | System.Drawing.FontStyle.Italic));