Piccolo trucco per legare uno skin ad un componente di Flex senza che venga restituito il seguente errore:

TypeError: Error #2007: Parameter child must be non-null.
 at flash.display::DisplayObjectContainer/addChildAt()
 at fl.controls::BaseButton/drawBackground()
 at fl.controls::BaseButton/draw()
 at fl.core::UIComponent/drawNow()
 at fl.controls::ScrollBar/draw()
 at fl.core::UIComponent/callLaterDispatcher()
TypeError: Error #2007: Parameter child must be non-null.
 at flash.display::DisplayObjectContainer/addChildAt()
 at fl.controls::BaseButton/drawBackground()
 at fl.controls::BaseButton/draw()
 at fl.core::UIComponent/callLaterDispatcher()
TypeError: Error #2007: Parameter child must be non-null.
 at flash.display::DisplayObjectContainer/addChildAt()
 at fl.controls::BaseButton/drawBackground()
 at fl.controls::LabelButton/draw()
 at fl.core::UIComponent/callLaterDispatcher()
TypeError: Error #2007: Parameter child must be non-null.
 at flash.display::DisplayObjectContainer/addChildAt()
 at fl.controls::BaseButton/drawBackground()
 at fl.controls::BaseButton/draw()
 at fl.core::UIComponent/callLaterDispatcher()
TypeError: Error #2007: Parameter child must be non-null.
 at flash.display::DisplayObjectContainer/addChildAt()
 at fl.controls::BaseButton/drawBackground()
 at fl.controls::BaseButton/draw()
 at fl.core::UIComponent/callLaterDispatcher()

Rendere non abilitato e invisibile il componente:

 var btn:Button = new Button();
 btn.setStyle( "upSkin", new Button_upSkin());
 btn.enabled = false;
 btn.visible = false;
 addChild( btn );

Questo permette di resettare lo skin.