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
feedbackEnabled = value;
    }
    /**
     * Sets whether auto scrolling and expanding should be provided during dragging.
     *
     * @param value <code>true</code> if scrolling and expanding is desired, and
     *   <code>false</code> if not
     * @since 2.0
     */
    public void setScrollExpandEnabled(boolean value) {
        scrollExpandEnabled = value;
    }
    /**
     * Validates dropping on the given object. This method is called whenever some 
     * aspect of the drop operation changes.
     * <p>
     * Subclasses must implement this method to define which drops make sense.
     * </p>
     * 
     * @param target the object that the mouse is currently hovering over, or
     *   <code>null</code> if the mouse is hovering over empty space
     * @param operation the current drag operation (copy, move, etc.)
     * @param transferType the current transfer type
     * @return <code>true</code> if the drop is valid, and <code>false</code>
     *   otherwise
     */
    public abstract boolean validateDrop(Object target, int operation,
            TransferData transferType);
}