how to assign value to WebDropdown on radiobutton selection.

i can't use below code because i want to do this on selection of radiobutton & in below case it will pass sender as Radiobutton. Please help me.

function dropDownClosed(sender, args) {

            var activeIndex = sender.get_activeItemIndex();

            var items = sender.get_items();

            if (activeIndex == 0 && items.getItem(0).get_selected() == true)

            {

                sender.set_currentValue("All", true); 

            }

            //var wdd = $find(_drpBatch);

            //__doPostBack(wdd, "");

        }