How to Create a Custom Action Filter for MVC 3 ?

What is an Action Filter ?

It's an Attribute
Could be applied on a particular Action
Could be applied on a Controller
It modifies the way Action Executes
An Action Filter is a class that inherits from the FilterAttribute base class
Filters are used to inject an extra logic into the MVC request processing
Filters to define logic which is used to apply add-on functionality to the application
e.g. defining Authorization, Caching, Logging, Exception etc.

What are the Types of Action Filters ?

What is 1-2-3-4 ?

If an Action Method has more than One Action Filter applied,
Then the order in which they are executed
i.e. Action Filters are Executed in the order 1-2-3-4
Firstly Executes Authorization Filters
Lastly Executes Exception Filters

What is an Authorization Filter ?

These filters are always run first before any other filters
They implement IAuthorizationFilter interface
Provides AuthorizeAttribute as the default class implementation

How to Do That ?

MyAuthorizationFilterAttribute.cs

using System.Web.Mvc;

namespace CustomActionFilter.CustomActionFilters

{

public class MyAuthorizationFilterAttribute:FilterAttribute,IAuthorizationFilter

{

public void OnAuthorization(AuthorizationContext filterContext)

{

if (filterContext.HttpContext.Request.IsAuthenticated)

{

//The action filter logic

}

HomeController.cs

using System.Web.Mvc;

using CustomActionFilter.CustomActionFilters;

namespace CustomActionFilter.Controllers

{

public class HomeController : Controller

{

[MyAuthorizationFilter]

public ActionResult Index()

{

ViewBag.Message = "Welcome to ASP.NET MVC!";

return View();

}

What is an Action Filter ?

It Implements IActionFilter interface
It Executes before and after action result is executed
Provides ActionFilterAttribute as the default class implementation

How to Do That ?

MyActionFilterAttribute.cs

using System.Web.Mvc;

namespace CustomActionFilter.CustomActionFilters

{

public class MyActionFilterAttribute : FilterAttribute, IActionFilter

{

public void OnActionExecuting(ActionExecutingContext filterContext)

{

//The action filter logic - before

}

public void OnActionExecuted(ActionExecutedContext filterContext)

{

//The action filter logic - after

}

HomeController.cs

using System.Web.Mvc;

using CustomActionFilter.CustomActionFilters;

namespace CustomActionFilter.Controllers

{

public class HomeController : Controller

{

[MyActionFilter]

public ActionResult Index()

{

ViewBag.Message = "Welcome to ASP.NET MVC!";

return View();

}

What is a Result Filter ?

It Implements IResultFilter interface
It Executes before and after action result is executed

How to Do That ?

MyResultFilterAttribute.cs

using System.Web.Mvc;

namespace CustomActionFilter.CustomActionFilters

{

public class MyResultFilterAttribute : FilterAttribute, IResultFilter

{

public void OnResultExecuting(ResultExecutingContext filterContext)

{

//The action filter logic - before

}

public void OnResultExecuted(ResultExecutedContext filterContext)

{

//The action filter logic - after

}

HomeController.cs

using System.Web.Mvc;

using CustomActionFilter.CustomActionFilters;

namespace CustomActionFilter.Controllers

{

public class HomeController : Controller

{

[MyResultFilter]

public ActionResult Index()

{

ViewBag.Message = "Welcome to ASP.NET MVC!";

return View();

}

What is an Exception Filter ?

It Implements IExceptionFilter interface
It Executes only if exception is thrown by action method or an action result
Provides HandleErrorAttribute as the default class implementation

How to Do That ?

MyExceptionFilterAttribute.cs

using System.Web.Mvc;

namespace CustomActionFilter.CustomActionFilters

{

public class MyExceptionFilterAttribute : FilterAttribute, IExceptionFilter

{

public void OnException(ExceptionContext filterContext)

{

if (filterContext.Exception != null)

{

//The action filter logic

}

HomeController.cs

using System.Web.Mvc;

using CustomActionFilter.CustomActionFilters;

namespace CustomActionFilter.Controllers

{

public class HomeController : Controller

{

[MyExceptionFilter]

public ActionResult Index()

{

ViewBag.Message = "Welcome to ASP.NET MVC!";

return View();

}

Note :

I have used VS 2010 with Asp.Net MVC 3 and C# for develop above code samples.

CustomActionFilter's Project Tree is as below :

Finally, the HomeController with All the Custom Action Filters are as below :

using System.Web.Mvc;

using CustomActionFilter.CustomActionFilters;

namespace CustomActionFilter.Controllers

{

public class HomeController : Controller

{

[MyAuthorizationFilter]

[MyActionFilter]

[MyResultFilter]

[MyExceptionFilter]

public ActionResult Index()

{

ViewBag.Message = "Welcome to ASP.NET MVC!";

return View();

}

That's It.You're Done.

Do you need to Download this Sample Project ?

Conclusion

Action Filters allow you to do some extra pre or post processing to be carried out,in addition to the code written in the action methods
Depending on your need you can implement IAuthorizationFilter, IActionFilter, IResultFilter or IExceptionFilter interfaces to make your filter an Authorization filter, Action filter, Result filter or Exception filter respectively
These interfaces decide the order in which the action filters are executed
Which makes your application more flexible and maintainable