Get index of the button inside CellRenderer

I have created many buttons inside the datagrid. Now when the user clicks on any button how can I know the index of the corresponding button.
I can get the index of the button in my file with
trace(“Button index is:”+button_index);

function setValue(str:String, item:Object, sel:Boolean) : Void
button._visible = (item != undefined);

I just want the index of the cell where button was pressed in the datagrid.
If 3rd button is pressed, how can I get this info?