We created this Feature Request to gather feedback on the way the item expansion is working in the Grid state. Currently, you can expand any items with the ExpandedRows collection of int where you pass the indexes of the rows.
Another option, which we are thinking of, is to provide a Collection<Model>. This would let you pass models, instead of indexes and the Grid would automatically expand those items. This approach would make the need to preserve the indexes redundant, which you should currently do when Filtering/Sorting and Grouping the items in the Grid.
We would appreciate your feedback on both approaches and which you think will be easier to use.