Removes all items.
<p>
This operation will fail when an item
could not be removed in the OS.
@exception SWTException <ul>
<li>ERROR_THREAD_INVALID_ACCESS when called from the wrong thread
<li>ERROR_WIDGET_DISPOSED when the widget has been disposed
</ul>
Removes all items. <p> This operation will fail when an item could not be removed in the OS.
@exception SWTException <ul> <li>ERROR_THREAD_INVALID_ACCESS when called from the wrong thread <li>ERROR_WIDGET_DISPOSED when the widget has been disposed </ul>