c# - Public variable loses value on button click event asp.net -

i have checkboxes in asp.net gridview , have method select multiple checkboxes , works great. after when user inputs value in textbox updated rows selected values set null again? have included method of checking multiple items , update button. why values not being retained , how can fix it?

public variables

public string values = ""; public string salesordernumber; 

multiple checkboxes

protected void selectcheckbox_oncheckedchanged(object sender, eventargs e) {     checkbox chk = sender checkbox;      var rows = dropdeadgridview.rows;     int count = dropdeadgridview.rows.count;     (int = 0; < count; i++)     {         bool ischecked = ((checkbox)rows[i].findcontrol("selectcheckbox")).checked;         if (ischecked)         {             values += rows[i].cells[1].text + ",";             rows[i].bordercolor = system.drawing.color.red;             rows[i].forecolor = system.drawing.color.red;             rows[i].borderstyle = borderstyle.inset;         }     } } 

update button

protected void updatebutton_click(object sender, eventargs e) {     app_code.griddata griddata = new app_code.griddata();          if (loadnumtextbox.text == "" && raddatetimepicker1.selecteddate != null)         {             sqlconnection dbconn = app_code.dbhelper.getconnection();             try             {                 using (dbconn)                 {                     sqlcommand addjob = new sqlcommand(@"update order_detail set dropdeadtime = @dropdeadtime sales_order_number = @salesordernumber", dbconn);                     //addjob.parameters.addwithvalue("@salesordernumber", convert.toint32(idtextbox.text));                     addjob.parameters.addwithvalue("@salesordernumber", values);                     addjob.parameters.addwithvalue("@dropdeadtime", raddatetimepicker1.selecteddate);                     dbconn.open();                     addjob.executenonquery();                 }                 notificationlabel.text = "updated!";                 notificationlabel.visible = true;             }             catch (exception ex)             {                 throw ex;             }              bindlist();         }          if (loadnumtextbox.text != "" && raddatetimepicker1.selecteddate == null)         {             sqlconnection dbconn = app_code.dbhelper.getconnection();             try             {                 using (dbconn)                 {                     sqlcommand addjob = new sqlcommand(@"update order_detail set load_number = @load_number sales_order_number = @salesordernumber", dbconn);                     addjob.parameters.addwithvalue("@salesordernumber", salesordernumber);                     addjob.parameters.addwithvalue("@load_number", loadnumtextbox.text);                     dbconn.open();                     addjob.executenonquery();                 }                 notificationlabel.text = "updated!";                 notificationlabel.visible = true;             }             catch (exception ex)             {                 throw ex;             }              bindlist();         } 

if want live between requests you'll have use session-state, view-state, cookie, or html form / request value.

asp.net stateless meaning not keep state post postback.

you need static 1 if want achieve goal.