Thanks for your reply, unfortunately this doesn't realy solve my problem. My setup needs virtualization instead of real paging. It is important for the user to be able to scroll through all groups, and when requested expand a group an scroll throug al entries within a group.
With the data we have it is possible that we have a lot of groups, but also possible that we have lots of entries within a group.
To be able to manage the number of rows ( Wich can be in the millions ), we only want to get the rows visible on the screen. So when grouping i'd first like to do a request to the server for (e.g.) groups 0 to 20, that contain the key and the child count. When the group is expanded I want to get a paged result of the containing elements, and when scrolling getting the needed elements.
I hope you understand what it is that I'm trying to achieve.