ASP.NET MVC Application_Error handler in Global.asax

Question

In Global.asax we have a class of type System.Web.HttpApplication named MvcApplication that represents the application and in which we can handle various events.

I'm interested in the Application_Error handler. In this handler we can use all the properties of the class MvcApplication.

-1-

Is always true that '(MvcApplication)sender' and 'this' are the same object?

protected void Application_Error(object sender, EventArgs e)
{
  var httpApp = (MvcApplication)sender;
  var equality1 = httpApp == this; // always true?
}

-2-

What is the best way to get the error? The following examples return the same error?

Exception ex0 = this.Context.Error;
Exception ex1 = httpContext.Error;
Exception ex2 = Server.GetLastError();
var equality3 = ex1 == ex2; // true?

Answer 1

Global.asax

protected void Application_Error(object sender, EventArgs e)
    {
        Exception exception = Server.GetLastError();
        Response.Clear();

        if (exception != null)
        {
            Common.WriteErrorLog(exception);
        }

        HttpException httpException = exception as HttpException;
        if (httpException != null)
        {
            RouteData routeData = new RouteData();
            routeData.Values.Add("controller", "Error");
            switch (httpException.GetHttpCode())
            {
                case 404:
                    // page not found
                    routeData.Values.Add("action", "HttpError404");
                    break;
                case 500:
                    // server error
                    routeData.Values.Add("action", "HttpError500");
                    break;
                default:
                    routeData.Values.Add("action", "Index");
                    break;
            }
            routeData.Values.Add("error", exception.Message);
            // clear error on server
            Server.ClearError();

            Response.RedirectToRoute(routeData.Values);
            // at this point how to properly pass route data to error controller?
            //Response.Redirect(String.Format("~/Error/{0}/?message={1}", "Index", exception.Message));
        }
    }

Controller :

public class ErrorController : Controller
{
    // GET: Error
    public ActionResult Index(string error="")
    {
        ViewBag.Message = error;
        return View();
    }

    public ActionResult HttpError404(string error = "")
    {
        ViewBag.Message = error;
        return View();
    }

    public ActionResult HttpError500(string error = "")
    {
        ViewBag.Message = error;
        return View();
    }
}