code: public void setItemAnimator(ItemAnimator animator) {
          if (mItemAnimator != null) {
              mItemAnimator.setListener(null);
          }
          mItemAnimator = animator;
          if (mItemAnimator != null) {
              mItemAnimator.setListener(mItemAnimatorListener);
          }
      }
docs: Sets the {@link com.twotoasters.android.support.v7.widget.RecyclerView.ItemAnimator} that will handle animations involving changes
  to the items in this RecyclerView. By default, RecyclerView instantiates and
  uses an instance of {@link com.twotoasters.android.support.v7.widget.DefaultItemAnimator}. Whether item animations are
  enabled for the RecyclerView depends on the ItemAnimator and whether
  the LayoutManager {@link com.twotoasters.android.support.v7.widget.RecyclerView.LayoutManager#supportsPredictiveItemAnimations()
  supports item animations}.
  
  @param animator The ItemAnimator being set. If null, no animations will occur
  when changes occur to the items in this RecyclerView.