SystemManager.keyDownHandler 监听整个Flex的keyDownHandler、mouseEventHandler
override protected function keyDownHandler(event:KeyboardEvent):void
{//super.keyDownHandler(event);
//如果按下了回车
if(event.keyCode==13)
{
//执行顺序
(tab 键就跳转了)
// UI---------->SystemManager.keyDownHandler----->FocusManager.keyDownHandler---------->自定义类重写的.keyDownHandler
// (类是否实现了IFocusManager)
//根据tabindex 移动焦点
focusManager.getNextFocusManagerComponent().setFocus();
}