Handle Session Timeout in .Net MVC Razor

问题

I am working on a website which is API based, client side is being developed in .Net MVC. For exception handling, I am using

 public void Application_Error(object sender, EventArgs e)
        {
            string action = "Index";
            Exception exception = Server.GetLastError();
            Response.Clear();

            HttpException httpException = exception as HttpException;

            if (httpException != null)
            {


                switch (httpException.GetHttpCode())
                {
                    case 404:
                        // page not found
                        action = "Error404";
                        break;
                    default:
                        action = "Index";
                        break;
                }

                // clear error on server
                Server.ClearError();
            }
            Response.Redirect(String.Format("/error/{0}", action));
        }

so for any exception thrown by try catch from Controller, the page redirects to error page.

Now I want that when session is expired it should redirect to Login page, How can I do that?

Right now what is happening is, after session expires, when I try to access the session value, it throws exception "object reference not set to an instance of object." then it redirects to the default error page.

回答1:

I don't think you're going to be able to do this from inside a generic exception handler because - as you said - missing session variables simply throw a NullReferenceException. Perform a null check on the session variable from your controller:

Public ActionResult MyAction ()
{
    if (Session["myVariable"] == null)
    {
        RedirectToAction("SessionTimeOut", "Error");
    }

    ...

}

If you have session variables that should always exist unless the session has expired, you could try overriding the OnActionExecuting method for your controller and performing your null check in there. To do this for multiple controllers, define a BaseController, override its OnActionExecuting method and then inherit this in your other controllers.

来源：https://stackoverflow.com/questions/13507224/handle-session-timeout-in-net-mvc-razor