RibbonBarSplitButton introduces the following properties, which can be used to define its behavior.
EnableButtonSelection allows buttons inside the drop-down to be selected as default,
once they are clicked. In the example you can select a Hat for instance, and this
will trigger several actions - update the image with the selected "hat", update
the text with the name of the selected hat and, last but not least, update the default
action of the split button.
SelectedButtonIndex on the other hand can be used, both, to select a button statically
(without the option of selecting another through a click in the drop-down) and in
combination with EnableButtonSelection=True, when it can be used to monitor the
selection for example, or to alter the default logic of EnableButtonSelection=True.
One important thing to mention about this feature of RibbonBarSplitButton is
the logic in which the image and text are updated:
The text of the split button is gathered from selected button only if it's not set (splitButton.Text=...)
The Image is updated as follows
if there is an applicable image set directly to the splitButton (splitButton.ImageUrl = ... or splitButton.DisabledImageUrlLarge etc.), it's applied
if there is no such image, the split button will try to apply an image from the SelectedButton. If there still isn't an image to apply, the default image is applied.