asp.net 验证码

Before proceeding with the topic first we must understand "What is a Captcha code?" and "Why do we use them?". Most web sites have a Captcha validation in their sites.

What is the Captcha code?

A Captcha code is simply a combination of some characters and numbers like "Alk13" or "aTu2eP" etc.

Why do we use them?

We use them for validating that the client browser window really has a human typing into it.

Ok, let's get to the topic i.e. creating your own Captcha code in ASP.Net.

Step 1

Go to Visual Studio and create a new project (web site or web application) say "CaptchCode".

Step 2

Now add a new page into your application say "ShowCaptcha.aspx" and add this code into the source for the page:

<div>
<table>
  <tr>
    <td>
      <asp:Image ID="imgCaptcha" runat="server" ImageUrl="~/CreateCaptcha.aspx?New=1"/>
     </td>
   </tr>
   <tr>
    <td>
      <asp:TextBox ID="txtCaptcha" runat="server"></asp:TextBox>
     </td>
    </tr>
    <tr>
     <td>
       <asp:Label ID="lblMessage" runat="server"></asp:Label>
      </td>
     </tr>
     <tr>
      <td>
 <asp:Button ID="btnCaptcha" runat="server" Text="Validate Cpatcha Code"                              onclick="btnCaptcha_Click" />
      </td>
       </tr>
     </table>
    </div>

Note: Here I am given the ImageUrl="~/CreateCaptcha.aspx?New=1" of the image control. In CreateCaptcha.aspx we will write the code for creating the Captcha code.

Step 3

Now add a new page into your application "CreateCaptcha.aspx" and create the following methods in its .cs file:

/// <summary>

/// method for create captcha image

/// </summary>

 private void CreateCaptchaImage()

{ 

 code = GetRandomText();

 Bitmap bitmap = new Bitmap(, , System.Drawing.Imaging.PixelFormat.Format32bppArgb);

 Graphics g = Graphics.FromImage(bitmap);

 Pen pen = new Pen(Color.Yellow);

 Rectangle rect = new Rectangle(, , , );

 SolidBrush blue = new SolidBrush(Color.CornflowerBlue);

 SolidBrush black = new SolidBrush(Color.Black);

 int counter = ;

 g.DrawRectangle(pen, rect);

 g.FillRectangle(blue, rect);

 for (int i = ; i < code.Length; i++)

 {

    g.DrawString(code[i].ToString(), new Font("Tahoma",  + rand.Next(, ), FontStyle.Italic), black, newPointF( + counter, ));

   counter += ;

 }

 DrawRandomLines(g);          

 bitmap.Save(Response.OutputStream, ImageFormat.Gif);

 g.Dispose();

 bitmap.Dispose();

}

/// <summary>

/// Method for drawing lines

/// </summary>

/// <param name="g"></param>

private void DrawRandomLines(Graphics g)

{

   SolidBrush yellow = new SolidBrush(Color.Yellow);

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

   {g.DrawLines(new Pen(yellow, ), GetRandomPoints());}

}

/// <summary>

/// method for gettting random point position

/// </summary>

/// <returns></returns>

private Point[] GetRandomPoints()

{

  Point[] points = { new Point(rand.Next(, ), rand.Next(, )), new    Point(rand.Next(, ), rand.Next(, )) };

  return points;

}

/// <summary>

/// Method for generating random text of 5 cahrecters as captcha code

/// </summary>

/// <returns></returns>

private string GetRandomText()

{

  StringBuilder randomText = new StringBuilder();          

  string alphabets = "012345679ACEFGHKLMNPRSWXZabcdefghijkhlmnopqrstuvwxyz";

  Random r = new Random();

  for (int j = ; j <= ; j++)

  {randomText.Append(alphabets[r.Next(alphabets.Length)]);}

    Session["CaptchaCode"] = randomText.ToString();

     return Session["CaptchaCode"] as String;

  }

Step 4 

To validate the Captcha code in the "ShowCaptcha.aspx.cs" page:

protected void btnCaptcha_Click(object sender, EventArgs e)

{

   //imgCaptcha.ImageUrl = "~/CreateCaptcha.aspx?New=0";

  if (Session["CaptchaCode"] != null && txtCaptcha.Text == Session["CaptchaCode"].ToString())

  {

     lblMessage.ForeColor = Color.Green;

     lblMessage.Text = "Captcha code validated successfully!!";

  }

  else

  {

   lblMessage.ForeColor = Color.Red;

   lblMessage.Text = "Captcha code is wrong!!";

  }

}

I hope this article will be helpful for you.

Happy Coding!!

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