c# - Redirect the user back to the source page from where it has come after succesfull login in asp.net -

hello guys working on small asp.net project final year project, making online shopping site. have 3 pages in site login.aspx, detail.aspx , mobile.aspx in mobile.aspx when user click on detail button redirect user detail.aspx page using response.redirect();(no problem in step). in detail.aspx page when user click on addtocart button page first check if user logged in or not(using session["authenticated"]!=null method) if logged in every thing goes ok according me problem comes when user not logged in , click on addtocart button redirect user login.aspx page in login page when user click on login button checks if user redirected detail page(using session["productid"]!=null) if yes should redirect user detail.aspx page not doing here code please me

login.aspx

protected void login1_authenticate(object sender, authenticateeventargs e) {     sqlconnection connection = new sqlconnection(conn);     connection.open();     cmd = new sqlcommand("select count(*) customer_login login_id = @a , pass_login=@b",connection);     cmd.parameters.addwithvalue("@a", login1.username);     cmd.parameters.addwithvalue("@b", login1.password);     string user_name;     int = convert.toint32(cmd.executescalar().tostring());      viewstate["previouspage"] = request.urlreferrer.tostring();//to retrive url redirected, used redirect user comes(detail.aspx)      if (i == 1)     {         e.authenticated = true;          session["authenticateduser"] = session.sessionid;         session["loginid"] = login1.username.tostring();         cmd = new sqlcommand("select f_name customer id = (select cust_id customer_login login_id = @a)", connection);         cmd.parameters.addwithvalue("@a", login1.username);         sdr = cmd.executereader();         sdr.read();         user_name = sdr["f_name"].tostring();         sdr.close();          if (session["productid"] != null&&viewstate["previouspage"].tostring())//to check if user redirected detail.aspx page         {             session["user"] = user_name.tostring();             response.redirect(viewstate["previouspage"].tostring());         }         else         {             session["user"] = user_name.tostring();              response.redirect("index.aspx");         }     }     else     {         e.authenticated = false;     } } 

the result of login redirect user index.aspx page not on detail page

i found solution used querystring in detail.aspx page send url of source page(detail.aspx)

            response.redirect("~/login.aspx?redirect="+request.url.tostring()); 

and retrieve login.aspx

        if (session["productid"] != null&&!string.isnullorempty(request.querystring["redirect"]))         {             session["user"] = user_name.tostring();             response.redirect(request.querystring["redirect"].tostring()+"&ssid="+session["authenticateduser"].tostring());       //response.redirect(viewstate["previouspage"].tostring());        // response.redirect("~/shop/cart.aspx?ssid="+session["authenticateduser"].tostring()+"&pr="+session["productid"].tostring());         }         else         {             session["user"] = user_name.tostring();              response.redirect("default.aspx");         }