I'm using RadControls for Silverlight Q3 2013 SP1.
I'm using RadGridView with a VirtualQueryableCollectionView as its ItemSource.
Our Grid might have up to 10.000.000 rows.
I'm using MVVM.
I need to update the grid's selection from my view model and vice versa (currently done via 2-way binding).
I need to send the selection to the server and I need to update the selection from the server (VM exchanges according messages with server).
I need to support ExtendedSelection.

Problem: If the user selects the first row, scrolls to the bottom and shift-selects the last row, all items in between are fetched from the server. While this works, it's definitely not acceptable when the grid has 10.000.000 rows. My first thought was to have something like an "index selection" which tells the server that "row 1 to row 10.000.000" has been selected (ignoring that items in between might not be selected for the moment. And the same kind of "indexed selection" when the server needs to update the selection of the UI. So in this case we would not need to fetch 10.000.000 items nor send all 10.000.000 selected item IDs from UI to server or the other way round. However, I think there is no support for such an "indexed selection" in RadGridView. So how can I solve this problem???

I've read the post listed below but they didn't help me:
http://www.telerik.com/forums/extended-selection-with-radgridview-and-virtualization
http://www.telerik.com/forums/radgridview-virtualqueryablecollectionview-selected-items-shift-click
http://www.telerik.com/forums/radgridview-virtualqueryablecollectionview-selected-items

Hope to hear from you soon.

Hello,

Generally the virtual collection was designed for ReadOnly purposes only and it is not recommended to be used in other scenarios. 

As to selection with VirtualQueryableCollectionView, it is only supported when the selected items are in the View area. I am afraid it is not possible to select items outside it as the item to be eventually displayed is still not presented. This is the case until the user scrolls to a particular position so that the items to be displayed into view are actually loaded.

I would suggest you to use QueryableCollectionView and DataPager intead.

I hope this helps.

Regards,
Didie
Telerik