RadToolBarSplitButton combines the functionality of RadToolBarButton and RadToolBarDropDown. When the user clicks the button it can respond by generating the client-side OnClientButtonClicking and OnClientButtonClicked events and the server-side ButtonClick event. It can also display a drop-down list when the user clicks its drop-down arrow.
The "push button" behavior of the split button can operate independently of its drop-down list, or it can represent one of the buttons in the drop-down list (the default button).
To allow the split button's "push button" behavior to act independently of the drop-down list, set the EnableDefaultButton property to False. When EnableDefaultButton is False, the split button is rendered using its own Text property and any Image properties you specify.
To allow the split button to represent a button in the drop-down list, set the EnableDefaultButton property to True (this is the default value). When EnableDefaultButton is True, the DefaultButtonIndex property identifies which button in its drop-down list is the default button. (DefaultButtonIndex is the index of the default button in the split button's Buttons collection). When EnableDefaultButton is True, the split button is rendered using the Text and image of the default button rather than the values assigned to its own Text and image properties.