public class BasePage : System.Web.UI.Page  
    {  
        protected override void OnInit(EventArgs e)  
        {  
            base.OnInit(e);  
            if (Session["User"] == null)  
            {  
                HttpContext context = HttpContext.Current;  
                context.Response.Redirect("Login.aspx?url=" + context.Request.Url.ToString());  
            }  
        }  
    }