image.aspx.cs

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using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Drawing;//引入命名空间

public partial class ValidateNum : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            string validateNum = CreateRandomNum(4);//成生4位随机字符串
            CreateImage(validateNum);//将生成的随机字符串绘成图片
            Session["image"] = validateNum.ToLower();//保存验证码
        }
    }
    //生成随机字符串
    private string CreateRandomNum(int NumCount)
    {
        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,v,w,x,y,z";
        string[] allCharArray = allChar.Split(',');//拆分成数组
        string randomNum = "";
        int temp = -1;//记录上次随机数的数值，尽量避免产生几个相同的随机数

        Random rand = new Random();
        for (int i = 0; i < NumCount; i++)
        {
            if (temp != -1)
            {
                rand = new Random(i * temp * ((int)DateTime.Now.Ticks));
            }
            int t = rand.Next(35);
            if (temp == t)
            {
                return CreateRandomNum(NumCount);
            }
            temp = t;
            randomNum += allCharArray[t];
        }
        return randomNum;
    }
    //生成图片
    private void CreateImage(string validateNum)
    {
        if (validateNum == null || validateNum.Trim() == String.Empty)
            return;
        //生成Bitmap图像
        System.Drawing.Bitmap image = new System.Drawing.Bitmap(validateNum.Length * 12 + 10, 22);
        Graphics g = Graphics.FromImage(image);

        try
        {
            //生成随机生成器