Returns the zero-relative index of the item which is currently
selected in the receiver, or -1 if no item is selected.
@return the index of the selected item
@exception SWTException <ul>
<li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li>
<li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li>
</ul>
Returns the zero-relative index of the item which is currently selected in the receiver, or -1 if no item is selected.
@return the index of the selected item
@exception SWTException <ul> <li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li> <li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li> </ul>