public AddRemoveGhostBlockUndoInstance(EditorUndoManager parent, GhostBlockInstance obj, bool created) : base(parent, obj.Room) { Created = created; UndoObject = obj; Valid = () => UndoObject != null && ((Created && UndoObject.Room != null) || (!Created && Room.ExistsInLevel)) && !Room.CoordinateInvalid(UndoObject.SectorPosition); UndoAction = () => { if (Created) { EditorActions.DeleteObjectWithoutUpdate(UndoObject); } else { var backupPos = obj.SectorPosition; // Preserve original position and reassign it after placement EditorActions.PlaceGhostBlockWithoutUpdate(Room, obj.SectorPosition, UndoObject); } }; RedoInstance = () => { var result = new AddRemoveGhostBlockUndoInstance(Parent, UndoObject, !Created); result.Room = Room; // Relink parent room return(result); }; }