When grid.enableVirtualScroll=true, the grid dispatches a virtualScroll event when the grid scrolls. This event contains a recordsToLoad array, which contains an series of VirtualScrollLoadInfo records. This provides the application a list of record indexes to load, and which levels to load them at.

In flat grids, the FlexDataGridVirtualScrollEvent.recordsToLoad will always contain a list of VirtualScrollLoadInfo records were level=1. For nested grids, depending on where the user scrolls and which items are open, you could get a list of records from multiple levels, for example. Records 1-3 from level 1, All children of record 3 from level 2, and then Record 4-10 from level 1.

Setting enableVirtualScroll requires that you specify childrenCountField as well as selectedKeyField. Additionally, enableVirtualScroll also requires that you set filterPageSortMode=server and itemLoadMode=server. Finally, virtual scroll does not work with variableRowHeights.