自定义ContextMenu不显示在MX TextArea中

        import mx.events.FlexEvent;

        public var nm:NativeMenu = new NativeMenu();
        public var cm:ContextMenu = new ContextMenu();

        protected function windowedapplication1_creationCompleteHandler(event:FlexEvent):void
        {
            cm.clipboardMenu = true;

            var cmi:ContextMenuItem = new ContextMenuItem(\"ctest\");
            cm.addItem(cmi);

            TA.contextMenu = cm;
        }

var cm:ContextMenu = new ContextMenu();

var menuitem:ContextMenuItem = new ContextMenuItem(\"Check Spelling\");
menuitem.addEventListener(ContextMenuEvent.MENU_ITEM_SELECT, handleContextMenuEvent);
mainMenu.addItem(menuitem);

textArea.contextMenu = mainMenu;
var txt:TextField = textArea.mx_internal::getTextField() as TextField;
txt.contextMenu = mainMenu;