Bug 72297 [DnD] ViewerDropAdapter impossible to set DND.FEEDBACK_NONE
It is not possible to disable selection feedback in ViewerDropAdapter. There are setFeedbackEnabled(false) and setScrollExpandEnabled(false) methods to turn off the feedback effects. If those methods are used, selection feedback still provided. It is not possible to turn it off, elements are still selected when drag is over them. Overriding method; private void setFeedback(DropTargetEvent event, int location) { event.feedback = DND.FEEDBACK_NONE; } - does not chenge the feedback either. setFeedbackEnabled() should be extended to disable SELECTION feedback or new method created, setSelectionFeedback().
bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/ViewerDropAdapter.java
*  and something more reasonable in other operating environments.
     * ]
     * </p>
     *
     * @param exception the exception
     * @param event the event
     */
    protected void handleException(Throwable exception, DropTargetEvent event) {
        
        
        
        exception.printStackTrace();
        event.detail = DND.DROP_NONE;
    }
    /**
     * Performs any work associated with the drop.
     * <p>
     * Subclasses must implement this method to provide drop behavior.
     * </p>
     *
     * @param data the drop data
     * @return <code>true</code> if the drop was successful, and 
     *   <code>false</code> otherwise
     */
    public abstract boolean performDrop(Object data);
    /* (non-Javadoc)
     * Method declared on DropTargetAdapter.
     * The mouse has moved over the drop target.  If the
     * target item has changed, notify the action and check
     * that it is still enabled.