生成验证码

新建一个专门用来创建验证码图片的页面image.aspx
它的后台cs文件代码如下：
PageLoad
private void Page_Load(object sender, System.EventArgs e)
        {
            string checkCode = CreateRandomCode(4);
             Session["CheckCode"] = checkCode;
             CreateImage(checkCode);
         }
其中CreateRandomCode是自定义的函数，参数代表验证码位数

private string CreateRandomCode(int codeCount)
        {
            string allChar = "0,1,2,3,4,5,6,7,8,9,A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,W,X,Y,Z" ;
            string[] allCharArray = allChar.Split(',');
            string randomCode = "";
            int temp = -1;

             Random rand = new Random();
            for(int i = 0; i < codeCount; i++)
            {
                if(temp != -1)
                {
                     rand = new Random(i*temp*((int)DateTime.Now.Ticks));
                 }
                int t = rand.Next(35);
                if(temp == t)
                {
                    return CreateRandomCode(codeCount);
                 }
                 temp = t;
                 randomCode += allCharArray[t];
             }
            return randomCode;
         }
CreateImage也是一个自定义的函数，用于生成图

private void CreateImage(string checkCode)
        {
            int iwidth = (int)(checkCode.Length * 11.5);
             System.Drawing.Bitmap image = new System.Drawing.Bitmap(iwidth, 20);
             Graphics g = Graphics.FromImage(image);
             Font f = new System.Drawing.Font("Arial", 10, System.Drawing.FontStyle.Bold);
             Brush b = new System.Drawing.SolidBrush(Color.White);
            //g.FillRectangle(new System.Drawing.SolidBrush(Color.Blue),0,0,image.Width, image.Height);
             g.Clear(Color.Blue);
             g.DrawString(checkCode, f, b, 3, 3);

             Pen blackPen = new Pen(Color.Black, 0);
             Random rand = new Random();
            for (int i=0;i<5;i++)
            {
                int y = rand.Next(image.Height);
                 g.DrawLine(blackPen,0,y,image.Width,y);
             }
           
             System.IO.MemoryStream ms = new System.IO.MemoryStream();
             image.Save(ms,System.Drawing.Imaging.ImageFormat.Jpeg);
             Response.ClearContent();
             Response.ContentType = "image/Jpeg";
             Response.BinaryWrite(ms.ToArray());
             g.Dispose();
             image.Dispose();
         }
//g.FillRectangle(new System.Drawing.SolidBrush(Color.Blue),0,0,image.Width, image.Height);
g.Clear(Color.Blue);
这两种方法都可以改变生成图片的背景颜色
下面那个for循环用来生成一些随机的水平线

在需要用到验证码的页面添加一个<asp:Image>控件即可，但是要把ImageUrl指向生成验证码的页面

<asp:Image Runat="server" ID="ImageCheck" ImageUrl="image.aspx"></asp:Image>
image.aspx代码页面

if(Session["CheckCode"]!=null)
    {
     string yzm=Session["CheckCode"].ToString().ToLower();
     if(this.yzm.Value.ToLower() == yzm)
     {
      //操作代码
     }
     else
     {
      Page.Response.Write("<script language=javascript>alert('验证码错误！');this.history.go(-1);</script>");
      Page.Response.End();
     }
    }