Hi Rui,
Please refer to our user guidance document regarding the same,
Additionally, the SelectedItems.CollectionChanged event will be triggered, when adding items to the SelectedItems collection. You can programmatically select more than one item by adding the underlying object to the SelectedItems property with SelectionMode as Multiple.
Please refer to our user guidance document regarding SelectedItems,
Please let us know if you need further assistance.
Lakshmi Natarajan