今天看见有人因img的src为空导致session丢失，以前一直没注意这个，所以晚上特地写了一段代码验证:
Default.aspx后台代码:
using System;
using System.Web;
using System.IO;
namespace src
{
public partial class _Default : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
WriteLog();
}
public static void WriteLog()
{
string _logFile = HttpContext.Current.Server.MapPath("log/log.txt");
using (StreamWriter sw = new StreamWriter(_logFile, true))
{
string s = string.Format("{0} {1}", HttpContext.Current.Request.Url.AbsoluteUri.ToString(), DateTime.Now.ToString());
sw.WriteLine(s);
sw.Close();
}
}
}
}
代码很简单，页面每次打开，都会在log/log.txt中追加一行记录，内容为“当前页的绝对网址+当前时间”前端测试代码:
<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="Default.aspx.cs" Inherits="src._Default" %> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml" > <head runat="server"> <title></title> </head> <body> <img alt="test" class="lazyload" src="data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAAAXNSR0IArs4c6QAAAARnQU1BAACxjwv8YQUAAAAJcEhZcwAADsQAAA7EAZUrDhsAAAANSURBVBhXYzh8+PB/AAffA0nNPuCLAAAAAElFTkSuQmCC" data-original="" /> </body> </html>
F5运行，发现log.txt确实有二行记录(在IE,FF,Chrome下都是同样的结果)
如果把<img alt="test" class="lazyload" src="data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAAAXNSR0IArs4c6QAAAARnQU1BAACxjwv8YQUAAAAJcEhZcwAADsQAAA7EAZUrDhsAAAANSURBVBhXYzh8+PB/AAffA0nNPuCLAAAAAElFTkSuQmCC" data-original="" /> 改成二个连续的img，即:
<img alt="test" class="lazyload" src="data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAAAXNSR0IArs4c6QAAAARnQU1BAACxjwv8YQUAAAAJcEhZcwAADsQAAA7EAZUrDhsAAAANSURBVBhXYzh8+PB/AAffA0nNPuCLAAAAAElFTkSuQmCC" data-original="" />
<img alt="test" class="lazyload" src="data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAAAXNSR0IArs4c6QAAAARnQU1BAACxjwv8YQUAAAAJcEhZcwAADsQAAA7EAZUrDhsAAAANSURBVBhXYzh8+PB/AAffA0nNPuCLAAAAAElFTkSuQmCC" data-original="" /> 运行后，页面仍被执行2次
继续测试，把<img alt="test" class="lazyload" src="data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAAAXNSR0IArs4c6QAAAARnQU1BAACxjwv8YQUAAAAJcEhZcwAADsQAAA7EAZUrDhsAAAANSURBVBhXYzh8+PB/AAffA0nNPuCLAAAAAElFTkSuQmCC" data-original="" /> 改为 <img alt="sss" class="lazyload" src="data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAAAXNSR0IArs4c6QAAAARnQU1BAACxjwv8YQUAAAAJcEhZcwAADsQAAA7EAZUrDhsAAAANSURBVBhXYzh8+PB/AAffA0nNPuCLAAAAAElFTkSuQmCC" data-original="" onerror="this.src='http://www.baidu.com/img/baidu_logo.gif'"/>，即图片加载错误时自动加载百度的logo，保证最终src肯定有值猜一下运行结果？结果与不加onerror完全相同，页面仍然执行二次！(有点意外吧？哈...)
go on! 这回干脆把class="lazyload" src="data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAAAXNSR0IArs4c6QAAAARnQU1BAACxjwv8YQUAAAAJcEhZcwAADsQAAA7EAZUrDhsAAAANSURBVBhXYzh8+PB/AAffA0nNPuCLAAAAAElFTkSuQmCC" data-original=""都去掉，即改成<img alt="test" />，再次竞猜结果？居然正常了，即仅执行了一次！(呵呵，看来多一事不如少一事)
最后再折腾一次，把src故意写成一个错误的地址，比如<img alt="test" class="lazyload" src="data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAAAXNSR0IArs4c6QAAAARnQU1BAACxjwv8YQUAAAAJcEhZcwAADsQAAA7EAZUrDhsAAAANSURBVBhXYzh8+PB/AAffA0nNPuCLAAAAAElFTkSuQmCC" data-original="http://abc.asdf.werdafsaf.sadfasdfas.xxx.gif" />结果正常，仅执行了一次！
结论:img标签的class="lazyload" src="data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAAAXNSR0IArs4c6QAAAARnQU1BAACxjwv8YQUAAAAJcEhZcwAADsQAAA7EAZUrDhsAAAANSURBVBhXYzh8+PB/AAffA0nNPuCLAAAAAElFTkSuQmCC" data-original=""时，会引起浏览器再次访问"./"即当前目录，如果该目录下有default.aspx,index.aspx等IIS的默认文档，则默认文档会执行2次 .
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