本文介绍了一种使用C#生成包含随机数字的验证码图片的方法。通过创建指定长度的随机数字字符串，并将其绘制到图片上，同时利用随机颜色增强图像安全性。文章还展示了如何设置HTTP响应头以正确返回生成的PNG图片。
<%@ Page Language="C#" %><%@ import Namespace="System.Drawing" %><%@ import Namespace="System.IO" %><%@ import Namespace="System.Configuration" %><%@ import Namespace="System.Web.Security" %><%@ import Namespace="System.Drawing.Imaging" %><script runat="server"> // Insert page code here // public string GetRandomNumberString(int int_NumberLength)
...{
string str_Number = string.Empty; Random theRandomNumber = new Random(); for (int int_index = 0; int_index < int_NumberLength; int_index++) str_Number += theRandomNumber.Next(10).ToString(); return str_Number;
} public Color GetRandomColor() ...{ Random RandomNum_First = new Random((int)DateTime.Now.Ticks); // 对于C#的随机数，没什么好说的 System.Threading.Thread.Sleep(RandomNum_First.Next(50)); Random RandomNum_Sencond = new Random((int)DateTime.Now.Ticks); // 为了在白色背景上显示，尽量生成深色 int int_Red = RandomNum_First.Next(256); int int_Green = RandomNum_Sencond.Next(256); int int_Blue = (int_Red + int_Green > 400) ? 0 : 400 - int_Red - int_Green; int_Blue = (int_Blue > 255) ? 255 : int_Blue; return Color.FromArgb(int_Red, int_Green, int_Blue); } public void CreateImage(string str_ValidateCode) ...{ int int_ImageWidth = str_ValidateCode.Length * 13; Random newRandom = new Random(); // 图高20px Bitmap theBitmap = new Bitmap(int_ImageWidth, 20); Graphics theGraphics = Graphics.FromImage(theBitmap); // 白色背景 theGraphics.Clear(Color.White); // 灰色边框 theGraphics.DrawRectangle(new Pen(Color.LightGray, 1), 0, 0, int_ImageWidth - 1, 19); // 10pt的字体 Font theFont = new Font("Arial", 10); for (int int_index = 0; int_index < str_ValidateCode.Length; int_index++)
...{ string str_char = str_ValidateCode.Substring(int_index, 1); Brush newBrush = new SolidBrush(GetRandomColor()); Point thePos = new Point(int_index * 13 + 1 + newRandom.Next(3), 1 + newRandom.Next(3)); theGraphics.DrawString(str_char, theFont, newBrush, thePos);
} // 将生成的图片发回客户端 MemoryStream ms = new MemoryStream(); theBitmap.Save(ms, ImageFormat.Png); Response.ClearContent(); //需要输出图象信息 要修改HTTP头 Response.ContentType = "image/Png"; Response.BinaryWrite(ms.ToArray()); theGraphics.Dispose(); theBitmap.Dispose(); Response.End(); } private void Page_Load(object sender, System.EventArgs e) ...{ if(!IsPostBack) ...{ // 4位数字的验证码 string str_ValidateCode = GetRandomNumberString(4); // 用于验证的Session Session["ValidateCode"] = str_ValidateCode; CreateImage(str_ValidateCode); } }</script><html><head></head><body></body></html>
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