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Implementing a custom error in global.asax

In my global.asax file, I have the following code:
void Application_Error(object sender, EventArgs e)
{
Exception TheError = Server.GetLastError();
if (TheError is HttpException && ((HttpException)TheError).GetHttpCode() == 404)
{
Response.Redirect("~/404.aspx");
}
else
{
Response.Redirect("~/500.aspx");
}
}
When I navigate to an non-existing page, I get the generic error page. I don't want anything pertaining to custom error in the web.config because my plan is to add code to the global.asax file to log the exceptions. Is there a way to handle custom error with just the global.asax file?

EDIT:
The answer is not obvious, but this seems to explain it: http://www.asp.net/web-forms/tutorials/deployment/deploying-web-site-projects/displaying-a-custom-error-page-cs
If you scroll down a ways, you'll find this lovely tidbit:
Note: The custom error page is only displayed when a request is made
to a resource handled by the ASP.NET engine. As we discussed in the
Core Differences Between IIS and the ASP.NET Development Server
tutorial , the web server may handle certain requests itself. By
default, the IIS web server processes requests for static content like
images and HTML files without invoking the ASP.NET engine.
Consequently, if the user requests a non-existent image file they will
get back IIS's default 404 error message rather than ASP.NET's
configured error page.
I've emphasized the first line. I tested this out in the default template, and sure enough, this URL:
http://localhost:49320/fkljflkfjelk
gets you the default IIS page, whereas simply appending a .aspx makes the Application_Error kick in. So, it sounds like you need to enable customErrors/httpErrors if you want to have all errors handled.
For IIS <= 6, add to <system.web>:
<customErrors mode="On" redirectMode="ResponseRewrite">
<error statusCode="404" redirect="/404.aspx"/>
<error statusCode="500" redirect="/500.aspx"/>
</customErrors>
For IIS7+, add to <system.webServer>:
<httpErrors errorMode="Custom">
<remove statusCode="404"/>
<error statusCode="404" path="/404.aspx" responseMode="ExecuteURL"/>
<remove statusCode="500"/>
<error statusCode="500" path="/500.aspx" responseMode="ExecuteURL"/>
</httpErrors>
I'll leave the original answer in case someone finds it useful.
I believe you need to clear the existing error code from the response, otherwise IIS ignores your redirect in favor of handling the error. There's also a Boolean flag, TrySkipIisCustomErrors, you can set for newer versions of IIS (7+).
So, something like this:
void Application_Error(object sender, EventArgs e)
{
Exception TheError = Server.GetLastError();
Server.ClearError();
// Avoid IIS7 getting in the middle
Response.TrySkipIisCustomErrors = true;
if (TheError is HttpException && ((HttpException)TheError).GetHttpCode() == 404)
{
Response.Redirect("~/404.aspx");
}
else
{
Response.Redirect("~/500.aspx");
}
}

Looks like IIS is looking for a page and did not find it.
Make sure:
404.aspx is created
customErrors tag from web.config is not present.

Not all errors catched by global.asax C#

I am attempting to catch all errors except '404-File not found' error in global.asax file and writing in to a text file in server,But lot of errors gets missed ,like FormatException Error,Sessionout Error and "Yellow Page of Error" Appears !
How can I catch all errors here.
void Application_Error(object sender, EventArgs e)
{
CT.Bussiness.DevCommonFunctions devTools = new CT.Bussiness.DevCommonFunctions();
HttpContext ctx = HttpContext.Current;
//ctx.Response.
// Get page url
if (ctx != null)
{
string pageName = ctx.Request.Url.ToString();
Exception ex = Server.GetLastError().GetBaseException();
HttpException checkException = (HttpException)ex;
if (checkException.GetHttpCode() != 404)
{
string errorDate = DateTime.Now.ToString();
//string pageName =pageName;
string errorMessage = ex.Message;
string errorSource = ex.Source;
//string errorInnerException=ex.InnerException.ToString();
string errorData = ex.Data.ToString();
string errorTarget = ex.TargetSite.ToString();
string errorStack = ex.StackTrace.ToString();
devTools.WriteErrorsIntoErrorLog(errorDate, pageName, errorMessage, errorSource, "InnerException", errorData, errorTarget, errorStack);
//devTools.SendErrorMail("developer3#devwebservices.net,developer4#devwebservices.net,developer5#devwebservices.net,hr#devwebservices.net", errorDate, pageName, errorMessage, errorSource, "InnerException", errorData, errorTarget, errorStack);
//Response.TrySkipIisCustomErrors = true;
Response.Redirect("~/Error.aspx");
//Response.Redirect("Error.aspx");
}
}
}
SOLVED
I Followed Like this as KPL Adviced below:
Implemented Elmah
Excluded Global.asax and
Wrote redirection code in web.config.
Thus Solved !

Use:
1.) web.config "customErrors" tag to avoid "Yellow Page of Error":
<customErrors mode="On" defaultRedirect="~/Error.aspx">
<error statusCode="400" redirect="/error/400-bad-request/" />
<error statusCode="404" redirect="/error/404-file-not-found/" />
<error statusCode="500" redirect="/error/500-server-error/" />
</customErrors>
2.) Also try using Elmah to logging errors.
ELMAH (Error Logging Modules and Handlers) is an application-wide error logging facility that is completely pluggable. It can be dynamically added to a running ASP.NET web application, or even all ASP.NET web applications on a machine, without any need for re-compilation or re-deployment.
Once ELMAH has been dropped into a running web application and configured appropriately, you get the following facilities without changing a single line of your code:
Logging of nearly all unhandled exceptions.
A web page to remotely view the entire log of recoded exceptions.
A web page to remotely view the full details of any one logged exception, including colored stack traces.
In many cases, you can review the original yellow screen of death that ASP.NET generated for a given exception, even with customErrors mode turned off.
An e-mail notification of each error at the time it occurs.
An RSS feed of the last 15 errors from the log.

ASP.NET 404 httpmodule

Im using a CMS product called EPiServer. We need to create our own method of displaying 404's which just can't be achieved using .NET's standard customErrors. We've writen a module which we use to check for the HttpStatusCode. We do this in the EndRequest method.
If the status is 404, we query EPiServer for the appropriate 404 page, and then Transfer the request over to that page. However this doesnt return a 404, and even if I do the following the correct status isnt returned:
HttpContext.Current.Response.StatusCode = 404;
HttpContext.Current.Response.StatusDescription = "Page not Found";
HttpContext.Current.Server.TransferRequest(newPage);
Likewise, if I do a response.redirect instead of a TransferRequest then its not a proper 404 because the url has then changed...
Whats the right way of doing this?
Thanks in advance
Al

Not a direct answer to your question but could also take a look at this open source 404 handler: https://www.coderesort.com/p/epicode/wiki/404Handler
It is also available on episervers nuget feed

Which IIS version are you using? For IIS7 or 7.5 you might need something like this:
<httpErrors errorMode="Custom">
<remove statusCode="404" />
<error statusCode="404" path="/somenotfoundpage.aspx" responseMode="ExecuteURL" />
<remove statusCode="500" />
<error statusCode="500" path="/someerrorpage.aspx" responseMode="ExecuteURL" />
</httpErrors>

You should set the status code in the codebehind of the template you're using for your 404 page.
If this is a plain content page, either create a new template or add a Status Code property to the page and logic in the code behind to send the appropriate header if this is not null or empty.

Try setting the status code on the page that you transfer to - in your error page template. I'm not sure that having a separate module is necessary - you can simply handle the HttpApplication's Error event in Global.asax.cs.

Thanks for your responses.
I actually got this working by doing the following:
In the EndRequest event handler I transferred the request off to the correct EPiServer page, and included a querystring param in the call i.e.
app.Context.Server.TransferRequest(pageUrl + "&internal=true");
Then in the PostRequestHandlerExecute event I check for the querystring param, if it exists it can only be because it's a 404 so I return the correct status:
HttpContext.Current.Response.StatusCode = 404;
HttpContext.Current.Response.StatusDescription = "Page not Found";
Works like a charm.
Thanks
higgsy

Custom HTTP error page

In asp.net, I can define a custom error page like this:
<configuration>
<system.web>
<customErrors mode="On">
<error statusCode="404" redirect="/servererrors/404.aspx" />
</customErrors>
</system.web>
</configuration>
Now my question: If I replace, say 404.aspx with AnyHTTP.aspx,
and want to get the number of the http error to generalize the page, how do I get that error numer?

Try this setting in CustomErrors (ASP.NET 3.5 SP1):
<customErrors mode="RemoteOnly" defaultRedirect="/servererrors/AnyHTTP.aspx" RedirectMode="ResponseRewrite"/>
As a different solution, you can also do this in Global.asax:
void Application_Error(object sender, EventArgs e)
{
Server.Transfer("/servererrors/AnyHTTP.aspx");
}
and on your error page, load the last error:
Exception e = Server.GetLastError();
It is important to use Server.Transfer() in the Global.asax file; using Response.Redirect will throw a 302 error and you will lose the error that you wanted to catch.

Well you might take a look at http://www.raboof.com/projects/Elmah/ before you venture to deep into doing your own thing...

I'd recommend not using the web.config method. customErrors redirects to the error page, which makes little sense. Essentially it first says "oh yes, that'll work perfectly, you just need to go here instead", and then says "oh, we didn't find that". That's really a bug (if there isn't anything here, then why did the server tell me to go here, clearly to the user code it looks like you the server code messed up; they went to the right URI and then you directed them to the wrong one).
Use Server.Transfer() from global.asax, set a default HTTPHandler, or set IIS to execute (not redirect to) your .aspx or other file with your implementation. If you want the same handler to manage each error, then you could, for example, do a Server.Transfer() from global.asax, but include a query string parameter about the type of error (whether simply an HTTP status code, or something more detailed), or pass information in the HttpContext.

Passing Exceptions to an error screen in ASP.net/C#

Coming from a desktop background I'm not sure exactly how to pass the exceptions I have caught to an Error page in order to avoid the standard exception screen being seen by my users.
My general question is how do I pass the exception from page X to my Error page in ASP.net?

I suggest using the customErrors section in the web.config:
<customErrors mode="RemoteOnly" defaultRedirect="/error.html">
<error statusCode="403" redirect="/accessdenied.html" />
<error statusCode="404" redirect="/pagenotfound.html" />
</customErrors>
And then using ELMAH to email and/or log the error.

The pattern I use is to log the error in a try/catch block (using log4net), then do a response.redirect to a simple error page. This assumes you don't need to show any error details.
If you need the exception details on a separate page, you might want to look at Server.GetLastError. I use that in global.asax (in the Application_Error event) to log unhandled exceptions and redirect to an error page.

We've had good luck capturing exceptions in the Global.asax Application_Error event, storing them in session, and redirecting to our error page. Alternately you could encode the error message and pass it to the error page in the querystring.

You can also get the exception from
Server.GetLastError();

Use the custom error pages in asp.net, you can find it in the customError section in the web.config

We capture the exception in the Global.asax file, store it in Session, the user is then redirected to the Error Page where we grab the exception for our Session variable and display the Message information to the user.
protected void Application_Error(object sender, EventArgs e)
{
Exception ex = Server.GetLastError();
this.Session[CacheProvider.ToCacheKey(CacheKeys.LastError)] = ex;
}
We do log the error message prior to displaying it the user.

I think you can use the global.asax -- Application_Exception handler to catch the exception and then store it for displaying in an error page.
But actually, your error page shouldn't contains code that might cause just another error. It should be simple "Oops! something went wrong" page.
If you want details on the error, use Windows' events viewer or ELMAH or employ some logging mechanism.