ASP.NET custom error page - Server.GetLastError() is null

Question

I have a custom error page set up for my application:

<customErrors mode="On" defaultRedirect="~/errors/GeneralError.aspx"
/>

In Global.asax, Application_Error(), the following code works to get the exception details:

  Exception ex = Server.GetLastError();
  if (ex != null)
    {
        if (ex.GetBaseException() != null)
            ex = ex.GetBaseException();
    }

By the time I get to my error page (~/errors/GeneralError.aspx.cs), Server.GetLastError() is null

Is there any way I can get the exception details on the Error Page, rather than in Global.asax.cs ?

ASP.NET 3.5 on Vista/IIS7

Answer 1

Looking more closely at my web.config set up, one of the comments in this post is very helpful: http://msdn.microsoft.com/en-us/library/h0hfz6fc.aspx

"in asp.net 3.5 sp1 there is a new parameter redirectMode"

so we can ammend customErrors to add this parameter thusly:

<customErrors mode="RemoteOnly" defaultRedirect="~/errors/GeneralError.aspx" redirectMode="ResponseRewrite" />

the ResponseRewrite mode allows us to load the Error Page without redirecting the browser, so the URL stays the same, and importantly for me, exception information is not lost.

Answer 2

I think you have a couple of options here.

you could store the last Exception in the Session and retrieve it from your custom error page; or you could just redirect to your custom error page within the Application_error event. If you choose the latter, you want to make sure you use the Server.Transfer method.

Answer 3

A combination of what NailItDown and Victor said. The preferred/easiest way is to use your Global.Asax to store the error and then redirect to your custom error page.

Global.asax:

    void Application_Error(object sender, EventArgs e) 
{
    // Code that runs when an unhandled error occurs
    Exception ex = Server.GetLastError();
    Application["TheException"] = ex; //store the error for later
    Server.ClearError(); //clear the error so we can continue onwards
    Response.Redirect("~/myErrorPage.aspx"); //direct user to error page
}

In addition, you need to set up your web.config:

  <system.web>
    <customErrors mode="RemoteOnly" defaultRedirect="~/myErrorPage.aspx">
    </customErrors>
  </system.web>

And finally, do whatever you need to with the exception you've stored in your error page:

protected void Page_Load(object sender, EventArgs e)
{

    // ... do stuff ...
    //we caught an exception in our Global.asax, do stuff with it.
    Exception caughtException = (Exception)Application["TheException"];
    //... do stuff ...
}

Answer 4

Try using something like Server.Transfer("~/ErrorPage.aspx"); from within the Application_Error() method of global.asax.cs

Then from within Page_Load() of ErrorPage.aspx.cs you should be okay to do something like: Exception exception = Server.GetLastError().GetBaseException();

Server.Transfer() seems to keep the exception hanging around.

Answer 5

One important consideration that I think everybody is missing here is a load-balancing (web farm) scenario. Since the server that's executing global.asax may be different than the server that's about the execute the custom error page, stashing the exception object in Application is not reliable.

I'm still looking for a reliable solution to this problem in a web farm configuration, and/or a good explanation from MS as to why you just can't pick up the exception with Server.GetLastError on the custom error page like you can in global.asax Application_Error.

P.S. It's unsafe to store data in the Application collection without first locking it and then unlocking it.