How do you handle session timeouts and expiration in ASP.NET Web Forms?

In ASP.NET Web Forms, you can handle session timeouts and expiration by implementing appropriate mechanisms to detect and respond to these events. Here's how you can handle session timeouts and expiration in ASP.NET Web Forms:

1. Session Timeout Detection:
   To detect a session timeout, you can handle the 'Session_Start' event in the 'Global.asax' file. This event is raised when a new session is started. You can use it to perform initialization tasks and set flags or variables indicating that the session has started. For example:

   
   
   void Session_Start(object sender, EventArgs e)
   {
       // Set session start flag or perform initialization
       Application["IsSessionActive"] = true;
   }
   
   

2. Session Expiration Handling:
   When a session expires, you can handle the 'Session_End' event in the 'Global.asax' file. This event is raised when a session ends, either due to timeout or explicit abandonment. You can use it to perform cleanup tasks or execute custom logic related to the expired session. For example:

   
   
   void Session_End(object sender, EventArgs e)
   {
       // Perform cleanup or custom logic for expired session
       Application["IsSessionActive"] = false;
   }
   
   

   It's important to note that the 'Session_End' event is not guaranteed to be raised in all scenarios, such as if the application pool is recycled or if the session state mode is configured differently.
3. Redirecting on Session Timeout:
   When a session timeout occurs, you can redirect the user to a designated page, such as a login page or a session timeout notification page. To achieve this, you can check the session state on each request and redirect the user if the session has expired. For example, you can create a base page or a common utility method to handle this redirection logic:

   
   
   protected void Page_Init(object sender, EventArgs e)
   {
       if (Session["IsSessionActive"] == null || !(bool)Session["IsSessionActive"])
       {
           // Redirect to a session timeout page or login page
           Response.Redirect("~/SessionTimeout.aspx");
       }
   }
   
   

   In the above example, the 'Page_Init' event handler is used to check the session state on each page initialization. If the session has expired (based on the 'IsSessionActive' flag set in 'Session_Start' and 'Session_End' events), the user is redirected to the session timeout page.
4. Handling AJAX Requests:
   If your application uses AJAX requests, you need to handle session timeouts appropriately. AJAX requests typically don't trigger a full page reload, so you need to detect and handle session timeouts specifically for AJAX requests. One approach is to include a mechanism in your AJAX requests to check the session state and respond accordingly. If the session has expired, you can return a specific status or error code indicating the timeout to the AJAX request, and your client-side JavaScript code can handle it appropriately.

   
   
   if (Session["IsSessionActive"] == null || !(bool)Session["IsSessionActive"])
   {
       // Return a specific status or error code to indicate session timeout
       Response.StatusCode = 440; // Custom status code indicating session timeout
       Response.End();
   }
   
   

   On the client-side, you can handle the returned status or error code in your AJAX error handler and perform the necessary actions, such as redirecting to a login page or displaying a session timeout message.

By implementing these mechanisms, you can handle session timeouts and expiration effectively in ASP.NET Web Forms and provide appropriate user experiences when sessions expire.