public void addUpdateListener(AnimatorUpdateListener listener){
  if (mUpdateListeners == null) {
    mUpdateListeners=new ArrayList<AnimatorUpdateListener>();
  }
  mUpdateListeners.add(listener);
}

public void addUpdateListener ( AnimatorUpdateListener listener ) { if ( mUpdateListeners == null ) { mUpdateListeners = new ArrayList < AnimatorUpdateListener > ( ) ; } mUpdateListeners . add ( listener ) ; }
adds a listener to the set of listeners that are sent update events through the life of an animation . this method is called on all listeners for every frame of the animation , after the values for the animation have been calculated .
