Display a mark indicating the point at which an item will be inserted.
The drop insert item has a visual hint to show where a dragged item
will be inserted when dropped on the tree.
@param item the insert item. Null will clear the insertion mark.
@param before true places the insert mark above 'item'. false places
the insert mark below 'item'.
@exception IllegalArgumentException <ul>
<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>
Display a mark indicating the point at which an item will be inserted. The drop insert item has a visual hint to show where a dragged item will be inserted when dropped on the tree.
@param item the insert item. Null will clear the insertion mark. @param before true places the insert mark above 'item'. false places the insert mark below 'item'.
@exception IllegalArgumentException <ul> <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>