Asp.net Web表单中的MVC异常过滤器等效项

Question

In MVC Web Forms, we have the error Filter by impementing IExceptionFilter. This ensures that any exception in the application will be routed here.

Is there an equivalent for this in ASP.Net? Is the Application_Error method invoked for all exceptions?

Answer 1

First, you should check through the official documentation.

You're asking about Web Forms, and then referring to ASP.NET, so I'm not really sure if you're asking about MVC or something else, but I am going to assume MVC. 1 & 3 apply regardless.

I found a nice Stackify article that is more condensed, which I'll paraphrase here. I'm going to ignore error handling that is not a global solution (HandleErrorAttribute, etc).

Depending on your needs, there are a few options for dealing with unhandled exceptions:

1) Generic Erorr pages configured in Web.Config section

<system.web>
    <customErrors mode="On" defaultRedirect="~/ErrorHandler/Index">
        <error statusCode="404" redirect="~/ErrorHandler/NotFound"/>
    </customErrors>
<system.web/>

If you set up something similar to the code above (replacing the example paths with paths to your error handler or other web pages), you can set up a default error page, as well as error pages for each type of status code. If you set mode="RemoteOnly", you'll only see these custom error pages when not on localhost, which can be very useful for debugging.

For example, I have the following in my project:

<customErrors mode="RemoteOnly" defaultRedirect="/ErrorHandler">
  <error statusCode="400" redirect="~/ErrorHandler/?errorCode=400" />
  <error statusCode="401" redirect="~/ErrorHandler/?errorCode=401" />
  <error statusCode="403" redirect="~/ErrorHandler/?errorCode=403" />
  <error statusCode="404" redirect="~/ErrorHandler/?errorCode=404" />
  <error statusCode="500" redirect="~/ErrorHandler/?errorCode=500" />
</customErrors>

This means that any generic exception with those status codes is automatically handles for me. ErrorHandler is a simple controller I created for this. However, this does not allow you to execute code on an unhandled exception, just display a generic error page.

2) Override OnException function on Controller

This requires you to set up an interface class for your controllers and to develop an override method for the controller's OnException method.

From the Stackify article, they develop a class named UserMvcController that inherits from Controller. I personally have a class named IBaseController that has this method, along with other methods, overridden.

An example of a simple interface:

public class UserMvcController : Controller
{
   protected override void OnException(ExceptionContext filterContext)
   {
      filterContext.ExceptionHandled = true;

      //Log the error!!
      _Logger.Error(filterContext.Exception);

      //Redirect or return a view, but not both.
      filterContext.Result = RedirectToAction("Index", "ErrorHandler");
      // OR 
      filterContext.Result = new ViewResult
      {
         ViewName = "~/Views/ErrorHandler/Index.cshtml"
      };
   }
} 

An example from one of my projects with a few other functions. All of these functions are available on your controllers if your controllers inherit from your base class:

public class IBaseController : Controller
{
    // Function to set up modal pup with Error styling
    public void Error(string errorHeader, string errorMessage)
    {
        ViewBag.ErrorHeader = errorHeader;
        ViewBag.ErrorMessage = errorMessage;
        ViewBag.JavaScriptHandler = "ShowErrorModal();";
    }

    // Function to set up modal pup with Informational styling
    public void Info(string infoHeader, string infoMessage)
    {
        ViewBag.InfoHeader = infoHeader;
        ViewBag.InfoMessage = infoMessage;
        ViewBag.JavaScriptHandler = "ShowInfoModal();";
    }

    // Function to override OnException method to pass exception info the ErrorController
    protected override void OnException(ExceptionContext filterContext)
    {
        filterContext.ExceptionHandled = true;

        //Redirect or return a view, but not both.
        filterContext.Result = RedirectToAction("Message", "ErrorHandler", new { area = "", errorException = filterContext.Exception.Message });
    }
}

As you can see, my OnException override simply passes some of the exception information to another controller to handle. I do not use it to log or trace anything. If you're using a controller, this method will be called on all unhandled exceptions.

3) Use Application_Error

In your Global.asax file, you can also set up the Application_Error() function to handle errors.

public class MvcApplication : System.Web.HttpApplication
{
   protected void Application_Start()
   {
      AreaRegistration.RegisterAllAreas();
      FilterConfig.RegisterGlobalFilters(GlobalFilters.Filters);
      RouteConfig.RegisterRoutes(RouteTable.Routes);
      BundleConfig.RegisterBundles(BundleTable.Bundles);
   }

   protected void Application_Error()
   {
      var ex = Server.GetLastError();
      //log the error!
      _Logger.Error(ex);
   }
}

This will allow you to do simple logging and generic types of error handling. I suppose you can implement something very robust here, but I prefer to do most of my logical handling within the controller.

Closing Remark

Personally, I prefer overriding the OnException method of the controller and handling my errors through there. I've found that by using that, and a well developed controller to handle errors, you can do some powerful things. There are even more options than these, but I think this will get you started.

Best.