passing id throw session in c# .net

Question

hi frnds how to  store id throw session and pass this session value another

 

i will use like this: 

 

if (chkBx != null && chkBx.Checked)

{

TextBox txt = (TextBox)di.FindControl("lbl_wokid");

Session["id"] =(txt);

}

 

store value in session["id"] and pass this value like: 

 

objadmin.Work_Id = Convert.ToInt32(Session["id"]); 

 

but getting error  

 

Unable to cast object of type 'System.Web.UI.WebControls.TextBox' to type 'System.IConvertible'.