ASP.NET MVC Controller.OnException not being called

Question

I have a base controller class where I'm overriding to the Controller.OnException handler method in order to provide a generic error handling for certain types of controllers that will inherit from this class (these are API controllers that will return JSON results). The OnException method never gets called when an exception gets raised by the controller. Does anyone see what I am doing wrong, or is there a better way to handle this situation?

Using MVC 1.0

Base Class:

public class APIController : Controller
    {

        protected override void OnException(ExceptionContext filterContext)
        {
           //This is never called
            filterContext.Result =
                new JsonResult(); 
            base.OnException(filterContext);
        }


    }

Inheriting Class:

public class MyController : APIController
    {
public AjaxResult ForcedException()
        {
            throw new SystemException();
        }
}

Answer 1

If I understand your question correctly - your Exception must be marked as "handled" in your OnException. Try this:

filterContext.ExceptionHandled = true;

Answer 2

The MSDN documentation (http://msdn.microsoft.com/en-us/library/system.web.mvc.controller.onexception.aspx) states that the OnException method is "called when an unhandled exception occurs in the action."

So, it sounds like it might only fire when an unhandled exception happens in an action method.

I created an new controller with one Index action. And the OnException method does in fact execute. I also tried throwing a SystemException() and the OnException method fired as well.

    public ActionResult Index ( )
    {
        throw new NotImplementedException ( );
    }

Answer 3

Are you calling the controller action from a unit test, or via ASP.NET? If you're calling the method directly in a test, say through NUnit, then OnException won't fire: the test framework will handle the exception and turn it into a failed test.

Answer 4

I was having exactly the same problem in my ASP.NET MVC 3 project.

It turns out that this is a feature of Visual Studio and the development server. When in debug mode you will be returned to Visual Studio and given the default exception dialog box.

One way to stop this from happening is to change the compilation mode in your Web.config from this:

<compilation debug="true" targetFramework="4.0">

To this:

<compilation debug="false" targetFramework="4.0">

You can also leave debug mode set to true but test your application is working by choosing the Start without debugging option from the visual studio menu (invoked by pressing Ctrl+F5.

Answer 5

The same rules apply for Controller.OnException as for HandleErrorAttribute

The required config for HandleErrorAttribute is noted here https://stackoverflow.com/a/528550/939634

If you have customError in your web.config set to mode="RemoteOnly" and you are debugging locally or you have mode="Off" the exceptions will not be handled and you will see the ASP.Net yellow screen with a stack trace.

If you set mode="On" or you are viewing the site remotely and have mode="RemoteOnly" your OnException method will execute properly.

Answer 6

Apply the [HandleError] attribute to the class.