selection of one item from ASP.Net ListBox

In that case check that is should not be rebind every time otherwise selections will be lost

its  binded everytime

1) populated at run time in postback as population depends on condition from user

2) so binded everytime

as per current flow i will have values only in the session variable

If you bind everytime the controls viewstate is lost hence selections will be lost. No hence bind only once

did not get

code i have

select name as theName from tab;le1 where name='"+textbox1.text+"'";
ddlValues;
ddlValues = cmd.ExecuteReader();

DropDownList1.DataSource = ddlValues;
DropDownList1.DataValueField = "theName";
DropDownList1.DataTextField = "theName";
DropDownList1.DataBind();

cmd.Connection.Close();
cmd.Connection.Dispose();

Meaning you should bind listbox only once on page load !ispostback so that the selections are retained. If you bind listbox on each postback what the user has selected will be lost