implement method regist unregist fig model event caus repaint necessari simplest fig regist listen event fire owner exampl fig link fig regist event fire associ owner associ shown link case need regist event notat provid us function call place creation load time fig owner chang case model chang function model chang function regist remov event owner fig delet owner get delet method call old owner owner equal listen owner safe ignor need updat listen relat element relat element replac param owner owner listen listen remov param old owner previou owner listen set updat listen object old owner object owner set object hash set object owner add object owner remov updat element listen 