Exception Handling in ASP.NET MVC 4

What does the user see when a runtime error occurs in an ASP.NET web application? The answer depends on how the website's <customErrors> configuration. By default, users are shown an unsightly yellow screen proclaiming that a runtime error has occurred. This tutorial shows how to customize settings to handle runtime exceptions.

We will use two attributes to handle error in an MVC application

• customErrors attribute defined in web.config
• HandleError attribute comes with default MVC Application

1. Set custom errors mode to ON in web config.
• From custom error we can set that where we can redirect a user when some exception occurs in our application.
• Set defaultRedirect attribute'value & add a sub tag for 404 error. Values for defaultRediret and redirect are the URLs of the pages for default redirection when some error occurs.


<!-- Custom Error Handling -->
<customErrors mode="On" defaultRedirect="~/Home/DefaultError">
<error statusCode="404" redirect="~/Home/Error404" />
</customErrors>





Use HandleError filter attribute


• The HandleError filter works only if the <customErrors> section is turned on in web.config.
• HandleError attribute provided by MVC framework.
• It handle only status code 500 errors. It does not handle 404 not found or other types of errors.
• If you use both customError attribute in web.config & HandleError attribute and any internal server error (500) occurs then HandleError will override behaviour of customError attribute & will handle error with it's own way.

Example of Controller level handling

[HandleError]
public class HomeController : Controller
{
    public ActionResult Index()
    {
        ViewData["Message"] = "Welcome to ASP.NET MVC!";

        return View();
    }

    public ActionResult About()
    {
        return View();
    }
}

3. You can use HandleError attribute at
• Action Level – by adding this attribute on Action ex. [HandleError]
• Controller Level - by adding this attribute on Controller ex. [HandleError]
• Application Level - by registering filter in FilterConfig.cs in App_Start folder

Example of Application level handling

     public class FilterConfig

   {

     public static void RegisterGlobalFilters(GlobalFilterCollection filters)

     {

     filters.Add(new HandleErrorAttribute());

     }

    }

3. When error occurs, this will redirect to a view which is in shared folder named 'Error'
4. You can change view name. ex. [HandleError(View = "DatabaseError")]
5. That's all
6. Redirection sequence of error handling
• For ( 500 Internal server error)
1. Redirect to view of Handle Error Attribute
2. Redirect to Url defaultRedirect defined in customErrors tag in web.config. ( if Handle Error is not registered at any level)
• For ( 404 or other types of errors)
1. Other url according to status code defined in customErrors tag.

Note:

1. Handle Error is an inbuilt Filter. We can use our own custom filter attribute by making a class which is derived from Filter Attribute & implements Iexception Filter interface.
2. To handle ajax request's exception. Visit the link given below.
3. For more detail about exception. Visit this link :
   http://www.dotnet-tricks.com/Tutorial/mvc/19D9140313-Exception-or-Error-Handling-and-Logging-in-MVC4.html