为什么要点两次button以后Session值才有效？
//btn
private void Button1_Click(object sender, System.EventArgs e)
{
Session[ "UserName "]= "abc ";
Page.Response.Redirect( "http://localhost/test/welcome.aspx);
}

//httpmodule
namespace test
{
public class UserAuthorizationModule : IHttpModule

{

#region IHttpModule 成员


public void Init(HttpApplication context)

{

context.AcquireRequestState += new EventHandler(context_AcquireRequestState);

}



void context_AcquireRequestState(object sender, EventArgs e)

{


HttpApplication application = (HttpApplication)sender;


if (application.Context.Session[ "UserName "] == null || application.Context.Session[ "UserName "].ToString().Trim() == " ")

{

string requestUrl = application.Request.Url.ToString();

string requestPage = requestUrl.Substring(requestUrl.LastIndexOf( '/ ') + 1);

if (requestPage != "login.aspx ")

application.Server.Transfer( "login.aspx ");

}


}


public void Dispose()

{ }

#endregion

}

调试时
在btn的事件里Session已经有值了，HttpContext.Session＝ "abc ",
但进httpmodule时HttpContext.Session就为空了
然后再点button以后进httpmodule时HttpContext.Session才是 "abc "
之后输地址加login.aspx再点btn的话也正常，就是第一次点btn时Session的值在httpmodule里为空，不知道为什么？

[解决办法]
用相对地址，别用绝对地址