Asp. NET generates random verification code

: (Flowing)

1. New folder for storing (bitmap) pictures in project

Graphic:

2, the front desk can add an ASP. NET control or any other to display the picture label, etc. (below)

    <div>        <asp:image id="Image1" runat="server " Imageurl=". /img/randomimg.gif" />    </div>

3. Generate random number (below)

        /// <summary>        ///Generate random numbers/// </summary>        /// <param name= "Codelength" ></param>        /// <returns></returns>         Public stringCreatecode (intcodelength) {            //I'm not doing this. Allow repetitive control, the reader needs to be able to do the appropriate control            stringso ="1,2,3,4,5,6,7,8,9,0,a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p,q,r,s,t,u,v,w,x,y,z,a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p,q, R,s,t,u,v,w,x,y,z"; string[] Strarr = so. Split (','); stringCode =""; Random Rand=NewRandom ();  for(inti =0; i < codelength; i++) {Code+ = Strarr[rand. Next (0, Strarr.length)]; }            returnCode; }

4, produce the verification picture (below)

        /// <summary>        ///generate a validation picture/// </summary>        /// <param name= "code" ></param>         Public voidCreateImage (stringcode) {            //set up Bitmap objects, (70,25) bitmap size controlBitmap image =NewBitmap ( -, -); //create a drawing layer based on the bitmap object created aboveGraphics g =graphics.fromimage (image); Webcolorconverter ww=NewWebcolorconverter (); G.clear ((Color) ww. ConvertFromString ("#FAE264"));//generate bitmap background colorRandom Random=NewRandom (); //draw a picture of the background noise line             for(inti =0; I < A; i++)            {                intX1 =Random. Next (image.                Width); intx2 =Random. Next (image.                Width); intY1 =Random. Next (image.                Height); inty2 =Random. Next (image.                                                Height); G.drawline (NewPen (Color.green), x1, y1, x2, y2);//Color.lightgray Noise Line Color            }            //Create a Font objectFont font =NewFont ("Arial", the, FontStyle.Bold |fontstyle.italic); System.Drawing.Drawing2D.LinearGradientBrush Brush=NewSystem.Drawing.Drawing2D.LinearGradientBrush (NewRectangle (0,0, image. Width, image. Height), color.red, Color.gray,1.2f,true); g.DrawString (code, font, brush,0,0); //draw the border line of a pictureG.drawrectangle (NewPen (Color.green),0,0, image. Width-0, image. Height-0); //temporarily Save (bitmap) PicturesImage. Save (Server.MapPath (".. /IMG") +"\\RandomImg.gif", System.Drawing.Imaging.ImageFormat.Gif); }

5, call (see below) (Note: Here I just to do the test, the reader should also consider the local refresh problem, here I do not make an explanation)

        protected void Page_Load (object  sender, EventArgs e)        {            string checkcode = Createcode (4 ); // 4 means to generate a            random number session["checkcode"] = checkcode;            CreateImage (Checkcode);        }

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