Asp.Net Mvc Result Filters Complete Guide

Example 1: Basic Result Filter

Let's start with a simple result filter that logs the type of action result being returned.

Step 1: Create the Result Filter

First, create a custom attribute class that implements IResultFilter.

using System.Web.Mvc;

public class LogResultAttribute : ActionFilterAttribute, IResultFilter
{
    public void OnResultExecuting(ResultExecutingContext filterContext)
    {
        // This method will be called before the action result is executed
        var controllerName = filterContext.ActionDescriptor.ControllerDescriptor.ControllerName;
        var actionName = filterContext.ActionDescriptor.ActionName;
        var resultType = filterContext.Result.GetType().Name;
        System.Diagnostics.Debug.WriteLine($"OnResultExecuting - Controller: {controllerName}, Action: {actionName}, ResultType: {resultType}");
    }

    public void OnResultExecuted(ResultExecutedContext filterContext)
    {
        // This method will be called after the action result is executed
        var controllerName = filterContext.ActionDescriptor.ControllerDescriptor.ControllerName;
        var actionName = filterContext.ActionDescriptor.ActionName;
        var resultType = filterContext.Result.GetType().Name;
        System.Diagnostics.Debug.WriteLine($"OnResultExecuted - Controller: {controllerName}, Action: {actionName}, ResultType: {resultType}");
    }
}

Step 2: Apply the Result Filter to a Controller or Action Method

You can apply this filter globally, to a specific controller, or to specific action methods. Here, we'll apply it to an individual action method in a controller.

public class HomeController : Controller
{
    [LogResult]
    public ActionResult Index()
    {
        return View();
    }

    [LogResult]
    public ActionResult About()
    {
        ViewBag.Message = "Your application description page.";

        return View();
    }
}

Now, when you access the /Home/Index or /Home/About URLs, you should see debug output indicating the types of results being executed and the controller/action names.

Example 2: Modifying the Action Result (Changing the View)

In this example, we will modify the action result to change which view is rendered even if a specific view was initially specified in the action method.

Step 1: Create the Result Filter Attribute

First, create a custom attribute class that modifies the action result.

public class ModifyResultAttribute : ActionFilterAttribute, IResultFilter
{
    public void OnResultExecuting(ResultExecutingContext filterContext)
    {
        var viewResult = filterContext.Result as ViewResult;
        if (viewResult != null && viewResult.ViewName == "Index")
        {
            // Change the view from "Index" to "ModifiedIndex"
            viewResult.ViewName = "ModifiedIndex";
        }
    }

    public void OnResultExecuted(ResultExecutedContext filterContext)
    {
        // This method will be called after the action result is executed
    }
}

Step 2: Create the Modified Views

Create two views: Index.cshtml and ModifiedIndex.cshtml. The Index.cshtml will show content for the original index view, and ModifiedIndex.cshtml will show modified content.

Index.cshtml

@{
    ViewBag.Title = "Index";
}

<div>
    <h1>This is the Index View</h1>
</div>

ModifiedIndex.cshtml

@{
    ViewBag.Title = "ModifiedIndex";
}

<div>
    <h1>This is the Modified Index View</h1>
</div>

Step 3: Apply the Result Filter

Apply the ModifyResultAttribute to the Index action method in the controller.

public class HomeController : Controller
{
    [ModifyResult]
    public ActionResult Index()
    {
        return View("Index"); // We intend to show the Index view
    }

    public ActionResult About()
    {
        ViewBag.Message = "Your application description page.";

        return View();
    }
}

Even though the action method returns the Index view, the result filter changes it to ModifiedIndex, so when you access the /Home/Index URL, you will see the ModifiedIndex view.

Example 3: Global Result Filter

Sometimes you might want to apply a result filter globally to all controllers and action methods in your application.

Step 1: Create the Filter

Create a result filter attribute as shown earlier. Here, we use the LogResultAttribute again.

public class LogResultAttribute : ActionFilterAttribute, IResultFilter
{
    public void OnResultExecuting(ResultExecutingContext filterContext)
    {
        var controllerName = filterContext.ActionDescriptor.ControllerDescriptor.ControllerName;
        var actionName = filterContext.ActionDescriptor.ActionName;
        var resultType = filterContext.Result.GetType().Name;
        System.Diagnostics.Debug.WriteLine($"OnResultExecuting - Controller: {controllerName}, Action: {actionName}, ResultType: {resultType}");
    }

    public void OnResultExecuted(ResultExecutedContext filterContext)
    {
        var controllerName = filterContext.ActionDescriptor.ControllerDescriptor.ControllerName;
        var actionName = filterContext.ActionDescriptor.ActionName;
        var resultType = filterContext.Result.GetType().Name;
        System.Diagnostics.Debug.WriteLine($"OnResultExecuted - Controller: {controllerName}, Action: {actionName}, ResultType: {resultType}");
    }
}

Step 2: Register the Filter Globally

To register thefilter globally, go to Global.asax.cs and add the filter to the GlobalFilters collection.

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

        // Registering the global result filter
        GlobalFilters.Filters.Add(new LogResultAttribute());
    }
}

With this registration, LogResultAttribute will run for all action methods in your application, regardless of which controller they belong to.

Summary

• Basic Result Filter: Logs the type of action result being returned.
• Modifying the Action Result: Changes the view from Index to ModifiedIndex.
• Global Result Filter: Applies a filter to all controllers and action methods globally.