Application_Error firing even for handled exceptions

Question

I have some code to display a button if a URL exists:

try
{
    string dashboardURL = Config.RootUrl + "/Dashboard/Default.aspx";
    WebRequest req = WebRequest.Create(dashboardURL);
    WebResponse response = req.GetResponse();
    btnDashboard.Visible = true;
}
catch (Exception)
{
    btnDashboard.Visible = false;
}

However, when debugging, req.getResponse() causes Application_Error to fire. I checked the exception being caught here and it is a System.Net.WebException. My understanding was that Application_Error is fired for unhandled exceptions.

If I change the code to force an exception as follows:

try
{
    string dashboardURL = Config.RootUrl + "/Dashboard/Default.aspx";
    WebRequest req = WebRequest.Create(dashboardURL);

    int j = 0;
    int i = 1 / j;

    WebResponse response = req.GetResponse();
    btnDashboard.Visible = true;
}
catch (Exception)
{
    btnDashboard.Visible = false;
}

then Application_Error is not fired, which is good. Is there something particular about handling errors with GetResponse() that always causes Application_Error to fire, even if the exception is handled?

Answer 1

Is the /Dashboard/Default.aspx in the same server/application?

If so then processing of that request can cause an error that will be captured by the Application_Error. The reason is that by doing GetResponse() you are doing a HTTP request, and any exceptions that happen while processing the request on (potentially) remote server will not be handled by try/catch on the calling code. In your special case remote server = local server, but the idea does not change.

Answer 2

In Application_Error check the exception:

var exception = Server.GetLastError();

It is impossible that Application_Error is fired with this code. Your exception must be after this try/catch Block.

Also try to Clean and Rebuild your solution, or force the Designer File to get recreated (Change something on aspx file).

I tested your code on different ASP.NET Version, even on MVC3/MVC4 Environment and Application_Error is never fired!