Overview Of Filters In MVC

How to create custom action filter

The custom action filters can be easily created by a class that is inherited by the ActionFilterAttribute class. This ActionFilterAttribute class is implemented by two interfaces - IActionFilter and IActionResult. So, we can override one of the methods in custom action filter. The ActionFilterAttribute class has four methods,

I have already explained about these four methods earlier, in this article. We can override any of these methods into our custom action filter class to implement the business logic.

Now, I am writing a class, MyCustomActionFilter, which is inherited by ActionFilterAttribute class and overrides all four methods for setting some ViewBag value into it.

Note

ActionFilterAttribute class comes into System.Web.Mvc namespace. Please have a look.

Our custom action filter is ready, and now, we need to use it into our action or on Controller but in this example, I am using it only in the Index Action method. For calling the action filter, we only need to simply decorate it on the action method or Controller by the class name inside the square bracket. Please see the given snapshot.

The code for Index View.

The output screen is shown below.

It is clearly visible that we did not assign any ViewBag value into the index method. We did it into our custom action filter and when our Index Action is executed, then we get the output with three ViewBag values. The fourth one is not visible on screen and that was assigned into OnResultExecuted method.

The OnResultExecuted executes at last on action method execution. This event will be executed after content is rendered to the View, so that time, content was rendering to the View and OnResultExecuted event could not be executed.

Different ways to use Action filters

Action Level

In the above example, I used this approach. I decorated our custom action filter only on Index Method .This filter will not apply on other action methods.

Controller Level

Sometimes, we want to write a logic that should execute in each action method of a Controller. Then, we decorate our Controller with the Custom Action Filter.

Global Filter

Sometimes, we want to write a logic that should execute for all action methods in an application. Then, we will register it as global filter. For registering it, we have to go in FilterConfig.cs file inside the App_Start folder, and register into RegisterGlobalFilters method (please see the image).