[HttpGet]
public ActionResult Home()
{
    if(Session["ID"] == null)
        return RedirectToAction("Login","Home");
}

We have to check the above 2 statements each time and in each ActionResult, but it may cause 2 problems.

1. Repeat Things: As per the good programming stranded, we don't have to repeat the things. Create a module of common code and access it multiple times/repeatedly
2. Code missing: We have to write code multiple times so it might happen some time we forget to write code in some method or we missed it.

How To Avoid?

The ASP.NET MVC provides a very great mechanism i.e., Action Filters. An action filter is an attribute. You can apply most action filters to either an individual controller action or an entire controller.
If you want to know more about action filter, please click here.

So we will create a custom Action Filter that handles session expiration and if session is null, redirect to Login Action.

Create a new class in your project and copy the following code:

namespace Mayur.Web.Attributes
{
    public class SessionTimeoutAttribute : ActionFilterAttribute
    {
        public override void OnActionExecuting(ActionExecutingContext filterContext)
        {
            HttpContext ctx = HttpContext.Current;
            if (HttpContext.Current.Session["ID"] == null)
            {
                filterContext.Result = new RedirectResult("~/Home/Login");
                return;
            }
            base.OnActionExecuting(filterContext);
        }
    }
}

Now our Action Filter is created and we are ready to use it. The following code will show you how we can apply attribute to Action or to complete controller.

1. Apply to Action

[HttpGet]
[SessionTimeout]
public ActionResult MyProfile()
{
    return View();
}

2. Apply to Controller

[SessionTimeout]
public class HomeController : Controller
{
    [HttpGet]
    public async ActionResult MyProfile()
    {
        return View();
    }

    [HttpGet]
    public async ActionResult MyQuestions()
    {
        return View();
    }

    [HttpGet]
    public async ActionResult MyArticles()
    {
        return View();
    }
}

Now all actions of Home Controller will check for session when hit with the help of Action Filter. So we have reduced the code and repetitive things. This is the benefits of Action Filters.

Happy coding !!!