Session state can only be used if EnableSessionState is set to true in the configuration file or Page directive. Also make sure to include System.Web.SessionSta in the//section of the application configuration

First understand our purpose, my purpose is to verify whether the user login, that is session["UserName"]!=null OK

At the beginning of the time I wrote this, the results of the error, the warning as above the title of the errors, checked the half-day data did not understand what the problem

   public class BasePage:System.Web.UI.Page    {public        basepage ()        } {this            . IsLogin ();        }        public void IsLogin ()        {            if (session["DateTime"] = = null)                Response.Redirect ("/webform1.aspx");}    }

Call base from the subclass. IsLogin () is normal but it's too much trouble to write every page, so you want to try to start the page

Try to verify that the OK code is as follows

   public class BasePage:System.Web.UI.Page    {        protected override void OnInit (EventArgs e)        {this            . IsLogin ();        }        public void IsLogin ()        {            if (session["DateTime"] = = null)                Response.Redirect ("/webform1.aspx");}    }

It's also clear why inside the constructor cannot be called

Know the Great god please answer next