static void gallery_Drop(object sender, DragEventArgs e) { e.Handled = true; if (dragableItem != null) { HitTestResult res = VisualTreeHelper.HitTest((GalleryControl)sender, e.GetPosition((GalleryControl)sender)); if (res.VisualHit == null) { return; } GalleryItemControl target = LayoutHelper.FindParentObject <GalleryItemControl>(res.VisualHit); if (target != null && target.Item != dragableItem) { GalleryItemCollection targetCollection = target.Item.Group.Items; GalleryItemCollection sourceCollection = dragableItem.Group.Items; int targetIndex = targetCollection.IndexOf(target.Item); if (targetCollection == sourceCollection) { targetCollection.Move(originalIndex, targetIndex); } else { sourceCollection.Remove(dragableItem); targetCollection.Insert(targetIndex, dragableItem); } dragableItem = null; } } }