Sets the item which is currently at the top of the receiver.
This item can change when items are expanded, collapsed, scrolled
or new items are added or removed.
@param item the item to be shown
@exception IllegalArgumentException <ul>
<li>ERROR_NULL_ARGUMENT - if the item is null</li>
<li>ERROR_INVALID_ARGUMENT - if the item has been disposed</li>
</ul>
@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>
Sets the item which is currently at the top of the receiver. This item can change when items are expanded, collapsed, scrolled or new items are added or removed.
@param item the item to be shown
@exception IllegalArgumentException <ul> <li>ERROR_NULL_ARGUMENT - if the item is null</li> <li>ERROR_INVALID_ARGUMENT - if the item has been disposed</li> </ul> @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>
@see Tree#getTopItem()
@since 2.1