Modal popup inside gridview

Question

I have a gridview which contain a button inside an item template..when i click that button a popup is shown using ajax modal popup extender..in that popup i have a dropdownlist and label.. i want to display the selected text of dropdown in label..how can it be done?? if the dropdown is auto post backed the popup will be closed...how to show popup always..

Note that popup is inside gridview..Please help