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;

public partial class getcode : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        //调用方法：
        //    <asp:Image ID="Image1" runat="server" ImageUrl="~/getcode.aspx" />
        //使用方法：
        //    if(Request["TextBox1"].Trim() == Session["GetCode"].ToString()){}
        if(!this.IsPostBack)
        {
            this.GenImg(this.GenCode(6));
        }

    }
    //产生随机字符串
    private string GenCode(int num)
   {
        string[] source={"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 code="";
        Random rd=new Random();
        for(int i=0;i < num;i++)
        {
            code += source[rd.Next(0,source.Length)];
        }
        return code;
   }

    //生成图片
    private void GenImg(string code)
    {
        Bitmap myPalette = new Bitmap(80, 20);//定义一个画板
        Graphics gh = Graphics.FromImage(myPalette);//在画板上定义绘图的实例
        Rectangle rc = new Rectangle(0, 0, 80, 20);//定义一个矩形

        gh.FillRectangle(new SolidBrush(Color.White), rc);//填充矩形
        gh.DrawString(code, new Font("Arial", 10), new SolidBrush(Color.Red), rc);//在矩形内画出字符串
        myPalette.Save(Response.OutputStream, System.Drawing.Imaging.ImageFormat.Gif);//将图片显示出来

        Session["GetCode"] = code;

        gh.Dispose();
        myPalette.Dispose();
    }

}