Tracking unhandled exception errors using Exception Filter in MVC.

 [Authorize(Roles="Administrator")]
        public ActionResult Contact()
        {
           ViewBag.Message = "Your contact page.";
	    return View();
     }

Action Filters:  It is used to access the action before and after the execution using override methods.  In the below code override method of Action filter is used to trace the action methods information. Two Override methods: OnActionExecuted, OnActionExecuting.  

public override void OnActionExecuted(ActionExecutedContext filterContext)
        {
            filterContext.ExceptionHandled = true;
        }

Result Filters: It is used to access the log information of action result methods. Two override methods- OnResultExecuted,OnResultExecuting. Mainly OutputCacheAttribute is used in Result filter.

public override void OnResultExecuted(ResultExecutedContext filterContext)
        {
            filterContext.ExceptionHandled = true;
        }

Exception Filter: - It is used to handle the unhandled anomalies exception at runtime. We will discuss more on Exception filter and will see an example as well.

Let s start to implement the Exception filter. We will create a sample project.

File > New> Project> Select MVC application.

Added below code to handle the exception. filtercontext is passed as a parameter to enable the exception. We are re-directing the Error page once exception occurs.

protected override void OnException(ExceptionContext filterContext)
        {
            filterContext.ExceptionHandled = true;
            filterContext.Result = new RedirectResult("~/Home/ErrorMessage");
            base.OnException(filterContext);
        }

Let’s see what will happen if we will not implement the override OnException method in the Home Controller, see below screen shot.

In the below screen shot shows how user encounter the error when any exception found.  We have created a new action methods and override the OnException method in Home controller.

Now we create new ErrorMessage action method which returns the Error page from View. Error Page will be available by default in the shared folder in the MVC 5 template.

public ActionResult ErrorMessage()
        {
            return View("Error");
        }

The below code, we tried to raise the exception when user hits the contact action method.

public ActionResult Contact()
        {
            throw new Exception("Exception occurred");
        }

Exception Filter Code Snippet.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Mvc;
namespace JkExceptionFilterDemo.Controllers
{
    public class HomeController : Controller
    {
       protected override void OnException(ExceptionContext filterContext)
        {
            filterContext.ExceptionHandled = true;
            filterContext.Result = new RedirectResult("~/Home/ErrorMessage");
            base.OnException(filterContext);
        }
        public ActionResult Index()
        {
            ViewBag.Message = "Modify this template to jump-start your ASP.NET MVC application.";
 
            return View();
        }
        public ActionResult About()
        {
            ViewBag.Message = "Your app description page.";
           return View();
        }
       public ActionResult Contact()
        {
            throw new Exception("Exception occuured");
        }
        public ActionResult ErrorMessage()
        {
            return View("Error");
        }
    }
}

After override the OnException method in the code, it shows the proper error message to the client and he can come back to Home page after click on Home Page without terminating the program.

When we click on Home page and  then we will see Home page of the appliation. And here we have handled the un recognized exception at the runtime. So we have done the Exception Filter in MVC.