[flexcoders] filter arraycollection with checkbox acting wired

[johndoematrix]

hi i am trying to filter an array collection using a checkbox, but
when i select the check box all the data disappears. here is my filter
function

private var pizzaSelected:Boolean;

private function pizzaFilter():void {
                if (pizza_ckb.selected == true)
                pizzaSelected = pizza_ckb.data;
                filterGrid();
                pizzaAr.refresh();      
            }


                        private function filterGrid() :void
                        {
                        pizzaAr.filterFunction=myFilterFunction;
                        pizzaAr.refresh();
                        }

                        private function myFilterFunction(item:Object): Boolean
                        {
                        return 
                        (item.pizza == pizzaSelected) ;
                        }

then on my pizza_ckb checkbox on the click event i call 
pizzaFilter(); is there something am doing wrong. if there is pizza
then the result is true and pizza records show if false nothing is
supposed to show up.