What are Action Filters in .Net and How to use Action Filters in .Net?

 Action Filters are a type of filter in the .NET framework that can be applied to controller actions or globally to all controller actions in an ASP.NET MVC application. Action Filters provide a way to execute code before or after the execution of an action method, or to modify the result of an action method.

Action Filters are implemented as attributes that can be applied to an action method, or to the entire controller class to apply to all action methods in that controller. Action Filters can be used to perform a wide range of tasks, including:

• Authorization: Determine if a user is authorized to access the action or resource.
• Validation: Validate input parameters or model data.
• Logging: Log information about the request, action, or result.
• Caching: Cache the result of an action method.
• Exception handling: Handle exceptions thrown by an action method.

Action Filters can be created by implementing the IActionFilter interface, which provides two methods: OnActionExecuting and OnActionExecuted. These methods are called before and after the execution of the action method, respectively.

Here's an example of an Action Filter that logs the start and end of an action method:

csharp
public class LogActionFilter : ActionFilterAttribute
{
    public override void OnActionExecuting(ActionExecutingContext filterContext)
    {
        // Log the start of the action method
        Log("Start of action method");
    }

    public override void OnActionExecuted(ActionExecutedContext filterContext)
    {
        // Log the end of the action method
        Log("End of action method");
    }

    private void Log(string message)
    {
        // Log the message using your logging framework of choice
        Console.WriteLine(message);
    }
}

In this example, the LogActionFilter class inherits from ActionFilterAttribute and overrides the OnActionExecuting and OnActionExecuted methods. These methods are called before and after the execution of the action method, respectively, and the Log method is used to log a message to the console.

To use this Action Filter, you can apply the LogActionFilter attribute to an action method or to the entire controller class, like this:

csharp
[LogActionFilter]
public ActionResult MyAction()
{
    // Do some work...
    return View();
}

When this action method is executed, the LogActionFilter will be applied and the start and end of the action method will be logged to the console.