Solution for the problem with: drag drop not accepted in HBox in Flex


private function dragEnterHandler(event:DragEvent):void {
   if (event.dragSource.hasFormat("some format"))
   {
     DragManager.acceptDragDrop(event.currentTarget as UIComponent);
   }
}

private function dragDropHandler(event:DragEvent):void {
   Alert.show("dropped");

}

.........
<mx:HBox id="v1" width="100%"  height="100%" label="dd" dragDrop="dragDropHandler(event);" dragEnter="dragEnterHandler(event);">
........
Here drop is not accepted by Hbox
solution: Just set the background of the container like: backgroundColor="#ffffff"

<mx:HBox id="v1" width="100%" backgroundColor="#ffffff" height="100%" label="dd" dragDrop="dragDropHandler(event);" dragEnter="dragEnterHandler(event);">