DropDownButtonBuilder.SelectedItemKey Method

Name	Parameters	Description
SelectedItemKey(JS)	value	Contains the selected item's key and allows you to specify the initially selected item. Applies when useSelectMode is true. Mirrors the client-side selectedItemKey option.
SelectedItemKey(Double)	value	Contains the selected item's key and allows you to specify the initially selected item. Applies when useSelectMode is true. Mirrors the client-side selectedItemKey option.
SelectedItemKey(String)	value	Contains the selected item's key and allows you to specify the initially selected item. Applies when useSelectMode is true. Mirrors the client-side selectedItemKey option.