/**
* {@link CanvasInfo} is "absolute container", but when we move {@link WidgetInfo} out, target
* container may be not "absolute". So, we should remove information related to "location".
*/
private void removeLocation_whenMoveOut() {
addBroadcastListener(new ObjectEventListener() {
@Override
public void childRemoveBefore(ObjectInfo parent, ObjectInfo child) throws Exception {
if (parent == CanvasInfo.this && child instanceof CanvasInfo) {
CanvasInfo canvas = (CanvasInfo) child;
removeLocation(canvas);