what is filters in asp.net mvc ?

Filters in ASP.NET MVC are attributes that allow you to add pre and post-processing logic to controller action methods. They provide a way to execute code before or after specific stages in the request processing pipeline. Filters help in addressing cross-cutting concerns such as logging, authorization, and error handling without cluttering the action methods with repetitive code.

Types of Filters in ASP.NET MVC:

1. Authorization Filters:

   • Used to implement authentication and authorization.
   • Example: [Authorize]

2. Action Filters:

   • Allow you to perform logic before and after an action method executes.
   • Example: [HandleError]

3. Result Filters:

   • Run before and after the execution of the action result.
   • Example: Custom result filters for modifying the response.

4. Exception Filters:

   • Used for handling exceptions raised by the action methods.
   • Example: [HandleError]

Example:

Here’s a simple example of a custom action filter in ASP.NET MVC:

public class CustomActionFilter : ActionFilterAttribute
{
    public override void OnActionExecuting(ActionExecutingContext filterContext)
    {
        // Code that runs before the action method executes
        var request = filterContext.HttpContext.Request;
        filterContext.HttpContext.Trace.Write("CustomActionFilter", "OnActionExecuting called");
        base.OnActionExecuting(filterContext);
    }

    public override void OnActionExecuted(ActionExecutedContext filterContext)
    {
        // Code that runs after the action method executes
        filterContext.HttpContext.Trace.Write("CustomActionFilter", "OnActionExecuted called");
        base.OnActionExecuted(filterContext);
    }
}

To use this custom action filter, you simply decorate your controller or action method with it:

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

In this example, the CustomActionFilter will log trace messages before and after the execution of the Index action method in the HomeController.

Hi,

Do refer below article 

https://www.c-sharpcorner.com/article/overview-on-types-of-filters-in-asp-net-mvc-5/

Here is the example,

Authorization Filter

public void OnAuthorization(AuthorizationContext filterContext)
{
    if (filterContext.HttpContext.Request.IsAuthenticated)
    {
        if (!Roles.IsUserInRole("Admin"))
        {
            ViewResult result = new ViewResult();
            result.ViewName = "Error";
            result.ViewBag.ErrorMessage = "Invalid User";
            filterContext.Result = result;
        }
    }
}

Action Filter

public class CustomActionfilter : FilterAttribute, IActionFilter
{
    public void OnActionExecuted(ActionExecutedContext filterContext)
    {
        if (filterContext.HttpContext.Session["UserID"] != null)
        {
            filterContext.Result = new RedirectResult("/Home/Index");
        }
        else
        {
            filterContext.Result = new RedirectResult("/Login /Login");
        }
    }

    public void OnActionExecuting(ActionExecutingContext filterContext)
    {
        if (filterContext.HttpContext.Session["UserID"] != null)
        {
            filterContext.Result = new RedirectResult("/Home/ Index");
        }
        else
        {
            filterContext.Result = new RedirectResult("/Login /Login");
        }
    }
}

[CustomActionfilter]
[AcceptVerbs(HttpVerbs.Get)]
public ActionResult GetPerson()
{
    Person p = new Person();
    return View("Person", p);
}

Result Filter

public class CustomResultfilter : FilterAttribute, IResultFilter
{
    public void OnResultExecuted(ResultExecutedContext filterContext)
    {
        if (filterContext.HttpContext.Session["UserID"] != null)
        {
            filterContext.Result = new RedirectResult("/Home/Contact");
        }
        else
        {
            filterContext.Result = new RedirectResult("/Login/Login");
        }
    }

    public void OnResultExecuting(ResultExecutingContext filterContext)
    {
        if (filterContext.HttpContext.Session["UserID"] != null)
        {
            filterContext.Result = new RedirectResult("/Home/Contact");
        }
        else
        {
            filterContext.Result = new RedirectResult("/Login/Login");
        }
    }
}

[CustomResultfilter]
[AcceptVerbs(HttpVerbs.Get)]
public ActionResult GetPerson()
{
    Person p = new Person();
    return View("Person", p);
}

Exception Filter

public class CustomExceptionFilter : FilterAttribute, IExceptionFilter
{
    public void OnException(ExceptionContext filterContext)
    {
        filterContext.Controller.ViewBag.onExceptionError = "ExceptionFilter filter called";
        filterContext.HttpContext.Response.Write("ExceptionFilter filter called");
    }
}

[CUstomExceptionFilter]
public class HomeController : Controller
{

}

https://www.c-sharpcorner.com/article/filters-in-Asp-Net-mvc-5-0-part-twelve/

https://www.c-sharpcorner.com/article/overview-on-types-of-filters-in-asp-net-mvc-5/

can you please reply with example?

Hello,

In ASP.NET MVC, a user request is routed to the appropriate controller and action method. However, there may be circumstances where you want to execute some logic before or after an action method executes. ASP.NET MVC provides filters for this purpose.

ASP.NET MVC Filter is a custom class where you can write custom logic to execute before or after an action method executes. Filters can be applied to an action method or controller in a declarative or programmatic way. Declarative means by applying a filter attribute to an action method or controller class and programmatic means by implementing a corresponding interface.

MVC provides different types of filters. The following table list filter types, built-in filters, and interface that must be implemented to create custom filters.

Thanks