Custom Action Filters in ASP.NET MVC

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Custom Action Filters in ASP.NET MVC

In this article, I am going to discuss how to create and use Custom Action Filters in ASP.NET MVC Application. Please read our previous article, where we discussed the RequireHttps attribute in MVC Application. At the end of this article, you will understand the following pointers.

1. What are Action Filters in MVC?
2. Why do we need Action Filters in ASP.NET MVC?
3. Why do we need Custom Action Filters in MVC?
4. How to create Custom Action Filter in ASP.NET MVC Application?

What are Action Filters in MVC?

An Action Filter in ASP.NET MVC Application is an attribute that can be applied either at the action methods of a controller or at the controller level directly. So, basically, action filters allow us to execute some custom code or logic either before executing an action method or immediately after the action method completes its execution

Why do we need Action Filters in the ASP.NET MVC Application?

As we already discussed, Filters in ASP.NET MVC are used to execute some custom code or logic at different levels of the request processing pipeline. The other advantage is that these Filters can be applied to multiple controllers or multiple action methods of different controllers which means it allows us to share the custom code or logic across Controllers.

For example, let’s say we want to execute some security code or some request and response logging code across the controllers. Then we can write a custom filter containing all those logic and apply that filter wherever you want to execute these custom logic. The following are some of the situations where you may use Filters.

1. Caching
2. Logging
3. Error Handling
4. Authentication and Authorization, etc.

How to create Custom Action Filter in ASP.NET MVC Application?

In the ASP.NET MVC application, we can create a custom action filter in two ways. They are as follows

1. First, by implementing the IActionFilter interface and inheriting the FilterAttribute class.
2. Second, by overriding the ActionFilterAttribute abstract class.

The IActionFilter interface includes the following methods to implement:

The ActionFilterAttribute abstract class includes the following methods which need to be overridden:

So, you can use any of the above approaches to create a Custom Action Filter in ASP.NET MVC Application. Let’s understand when the above four methods are going to be executed.

1. OnActionExecuting(ActionExecutingContext filterContext)- This method is going to be execute before executing a controller action method.
2. OnActionExecuted(ActionExecutedContext filterContext)- This method is called after a controller action method is executed.
3. OnResultExecuting(ResultExecutingContext filterContext)- This method is called before a controller action result is executed.
4. OnResultExecuted(ResultExecutedContext filterContext)- This method is called after a controller action result is executed.

Example:

Let us consider a scenario of Logging. For every incoming request, we need to log some data to the files on the basis of some logic. If we don’t create this logic inside a custom filter, then we will have to write the same logic for each controller’s action. This mechanism will lead to two problems:

1. Duplication of code; and
2. Violation of the Single Responsibility Principles. That means action methods will now perform additional tasks of logging.

We can solve the above two problems by putting the logging logic inside a custom action filter and applying the filter at all the controllers’ levels.

Creating a new ASP.NET MVC Application

Open visual studio and select File => New => Project from the context menu as shown in the below image.

Once you click on the “Project” link, a new dialog will pop up. From that window, we are going to choose “Web” templates from the left pane. From the middle pane, we need to select “ASP.NET Web Application“. Then provide a meaningful name to the project such as “CustomActionFilter”. Finally, click on the “OK” button as shown in the below image

Once you click on the “OK” button a new dialog will pop up with the name “New ASP.NET Project” for selecting project Templates as shown in the below image.

In this dialog, we are going to choose the “Empty” and “MVC” project template with the Authentication type as “No Authentication” and then click on the “OK” button. Once you click on the OK button it will take some time to create the project for us.

Adding Log Folder:

Let’s add a folder called Log into the project’s root directory. To do so, just right-click on the “CustomActionFilter” project and then select Add ➜ “New Folder“ and name it as Log. In this folder, we are going to create a text file with the Log.txt where we will store the Log data.

Creating Custom Action Filter in MVC:

Create a class file with the name LogFilter.cs within the Models folder and then copy and paste the following code in it.

using System.Web;
using System;
using System.Web.Mvc;
using System.IO;
using System.Web.Routing;

namespace CustomActionFilter.Models
{
    public class LogFilter : FilterAttribute, IActionFilter
    {
        public void OnActionExecuted(ActionExecutedContext filterContext)
        {
            Log("OnActionExecuted", filterContext.RouteData);
        }

        public void OnActionExecuting(ActionExecutingContext filterContext)
        {
            Log("OnActionExecuting", filterContext.RouteData);
        }

        private void Log(string methodName, RouteData routeData)
        {
            var controllerName = routeData.Values["controller"];
            var actionName = routeData.Values["action"];

            string message = methodName + " Controller:" + controllerName + " Action:" + actionName + " Date: "
                            + DateTime.Now.ToString() + Environment.NewLine;
            
            //saving the data in a text file called Log.txt
            File.AppendAllText(HttpContext.Current.Server.MapPath("~/Log/Log.txt"), message);
        }
    }
}

Here we use the first version of creating a Custom Action Filter. That is by implementing the IActionFilter interface and inheriting from FilterAttribute class so that we can use this class as a Filter.

Using the Custom Action Filter in ASP.NET MVC:

Create a Controller with the name Home Controller and then copy and paste the following code into it.

using System.Web.Mvc;
using CustomActionFilter.Models;

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

        public ActionResult Contact()
        {
            return View();
        }
    }
}

Creating the Index and Contact Views:

Index.cshtml

@{
    ViewBag.Title = "Index";
}
<h2>Index View</h2>

Contact.cshtml

@{
    ViewBag.Title = "Contact";
}
<h2>Contact View</h2>

Now run the application and navigate to different pages and see the text file.

Creating a Custom Action Filter using ActionFilterAttribute:

Let us modify the LogFilter class as shown below to override the ActionFilterAttribute.

using System.Web;
using System;
using System.Web.Mvc;
using System.IO;
using System.Web.Routing;

namespace CustomActionFilter.Models
{
    public class LogFilter : ActionFilterAttribute
    {
        public override void OnActionExecuted(ActionExecutedContext filterContext)
        {
            Log("OnActionExecuted", filterContext.RouteData);
        }

        public override void OnActionExecuting(ActionExecutingContext filterContext)
        {
            Log("OnActionExecuting", filterContext.RouteData);
        }

        public override void OnResultExecuting(ResultExecutingContext filterContext)
        {
            Log("OnResultExecuting", filterContext.RouteData);
        }

        public override void OnResultExecuted(ResultExecutedContext filterContext)
        {
            Log("OnResultExecuted", filterContext.RouteData);
        }

        private void Log(string methodName, RouteData routeData)
        {
            var controllerName = routeData.Values["controller"];
            var actionName = routeData.Values["action"];

            string message = methodName + " Controller:" + controllerName + " Action:" + actionName + " Date: "
                            + DateTime.Now.ToString() + Environment.NewLine;
            
            //saving the data in a text file called Log.txt
            File.AppendAllText(HttpContext.Current.Server.MapPath("~/Log/Log.txt"), message);
        }
    }
}

As you can see, now the LogFilter class is derived from the ActionFilterAttribute abstract class and we also override all four methods. Now, it logs before and after the action method or result executes. You can apply the Log attribute to any Controller or action method where you want to log the action. Run the application and open the Log.txt file which is inside Log Folder and checks the log that is generated by the Log Filter.

In the next article, I am going to discuss Filter Overrides in ASP.NET MVC Application. Here, in this article, I try to explain how to create and use the Custom Action Filters in the ASP.NET MVC application with a simple example. I hope you understood how to create and consume Custom Action Filters in the ASP.NET MVC application.