When used with a data-virtualized (asynchronous) source, this property will throw an exception; BeginGetSelectedItems and EndGetSelectedItems should be used in this situation.
For a listbox whose SelectionMode is set to Multiple or Extended, the SelectedItems property returns a list that contains the selected items.
For a listbox whose SelectionMode is set to Single, the SelectedItems property returns a list that contains the selected item. For a single-selection listbox, the selected item can also be retrieved by using the SelectedItem property or the index of the selected item by using the SelectedIndex property.
Target Platforms: Windows 11, Windows 10, Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2