Asp.Net Mvc Introduction To Filters Complete Guide

Step 1: Understanding ASP.NET MVC Filters

Filters in ASP.NET MVC are attributes that allow you to apply certain behaviors before or after the execution of controllers or controller actions. The primary types of filters are:

1. Authorization Filters
2. Action Filters
3. Result Filters
4. Exception Filters

Step 2: Setting Up a New ASP.NET MVC Project

1. Open Visual Studio and create a new project.
2. Select "ASP.NET Web Application (.NET Framework)".
3. Choose "MVC" template and click "Create".

Step 3: Creating a Simple Controller

Let’s start with a simple controller to demonstrate the usage of filters.

// Controllers/HomeController.cs

using System.Web.Mvc;

public class HomeController : Controller
{
    public ActionResult Index()
    {
        ViewBag.Message = "Welcome to the ASP.NET MVC Filters demo!";
        return View();
    }

    public ActionResult About()
    {
        ViewBag.Message = "This is the About Page";
        return View();
    }

    public ActionResult Contact()
    {
        ViewBag.Message = "Contact us at support@example.com";
        return View();
    }
}

Step 4: Implementing Authorization Filter

Authorization filters are used to control access to controller actions.

// Filters/CustomAuthorizationFilter.cs

using System.Web.Mvc;

public class CustomAuthorizationFilter : AuthorizeAttribute
{
    protected override bool AuthorizeCore(HttpContextBase httpContext)
    {
        // Custom authorization logic here
        if (httpContext.User.Identity.IsAuthenticated)
        {
            return true;
        }
        return false;
    }

    protected override void HandleUnauthorizedRequest(AuthorizationContext filterContext)
    {
        filterContext.Result = new RedirectToActionResult("Unauthorized", "Home");
    }
}

Apply the filter to the About action in the HomeController:

// Controllers/HomeController.cs

[CustomAuthorizationFilter]
public ActionResult About()
{
    ViewBag.Message = "This is the About Page";
    return View();
}

Add an Unauthorized action to HomeController:

// Controllers/HomeController.cs

public ActionResult Unauthorized()
{
    ViewBag.Message = "You are not authorized to access this page.";
    return View("Unauthorized");
}

Step 5: Implementing Action Filter

Action filters allow you to execute code before and after the action method is called.

// Filters/CustomActionFilter.cs

using System.Web.Mvc;

public class CustomActionFilter : ActionFilterAttribute
{
    public override void OnActionExecuting(ActionExecutingContext filterContext)
    {
        filterContext.Controller.ViewBag.ActionExecuting = "OnActionExecuting called";
    }

    public override void OnActionExecuted(ActionExecutedContext filterContext)
    {
        filterContext.Controller.ViewBag.ActionExecuted = "OnActionExecuted called";
    }
}

Apply the filter to the Index action in the HomeController:

// Controllers/HomeController.cs

[CustomActionFilter]
public ActionResult Index()
{
    ViewBag.Message = "Welcome to the ASP.NET MVC Filters demo!";
    return View();
}

Step 6: Implementing Result Filter

Result filters allow you to execute code before and after the view is rendered.

// Filters/CustomResultFilter.cs

using System.Web.Mvc;

public class CustomResultFilter : ResultFilterAttribute
{
    public override void OnResultExecuting(ResultExecutingContext filterContext)
    {
        filterContext.Controller.ViewBag.ResultExecuting = "OnResultExecuting called";
    }

    public override void OnResultExecuted(ResultExecutedContext filterContext)
    {
        filterContext.Controller.ViewBag.ResultExecuted = "OnResultExecuted called";
    }
}

Apply the filter to the About action in the HomeController:

// Controllers/HomeController.cs

[CustomResultFilter]
public ActionResult About()
{
    ViewBag.Message = "This is the About Page";
    return View();
}

Step 7: Implementing Exception Filter

Exception filters are used to handle exceptions that occur during the execution of an action or any filters applied to it.

// Filters/CustomExceptionFilter.cs

using System.Web.Mvc;

public class CustomExceptionFilter : ExceptionFilterAttribute
{
    public override void OnException(ExceptionContext filterContext)
    {
        filterContext.ExceptionHandled = true;
        filterContext.Result = new ViewResult
        {
            ViewName = "Error"
        };

        filterContext.Controller.ViewBag.ExceptionMessage = filterContext.Exception.Message;
    }
}

Apply the filter globally in Global.asax.cs:

// Global.asax.cs

protected void Application_Start()
{
    AreaRegistration.RegisterAllAreas();
    FilterConfig.RegisterGlobalFilters(GlobalFilters.Filters);
    RouteConfig.RegisterRoutes(RouteTable.Routes);
    BundleConfig.RegisterBundles(BundleTable.Bundles);

    // Register the custom exception filter globally
    GlobalFilters.Filters.Add(new CustomExceptionFilter());
}

Create an Error view in the Views/Shared folder:

<!-- Views/Shared/Error.cshtml -->

@{
    ViewBag.Title = "Error";
}

<h2>An error occurred while processing your request.</h2>
<p>@ViewBag.ExceptionMessage</p>

Step 8: Testing the Filters

1. Run the application.

2. Access the Index action.

   • Check if ViewBag.ActionExecuting and ViewBag.ActionExecuted messages are displayed on the Index view.
   • Check if ViewBag.ResultExecuting and ViewBag.ResultExecuted messages are displayed on the Index view.

3. Access the About action.

   • If you are not authenticated, you should be redirected to the Unauthorized view.
   • Check if ViewBag.ResultExecuting and ViewBag.ResultExecuted messages are displayed on the About view.

4. Access a non-existing action.

   • You should be redirected to the Error view with the exception message.