Hello!
I can catch the displayed items change in combobox?
(I use dataprovider in combobox.)
I was thinking about the first. Thank you 
Do you need a method to know whether an item is currently shown in popup panel or not (i.e. user can see it, it is not outside the shown page/scrolled out)? There is no method for this at the moment.
Or do you need a method to update item in CombBox since you have changed it? This is done with DataProvider.refreshItem(…) method.
Yes. It would required custom extension to be implemented, so that shown items can be read from client side.