code: @Override
      protected boolean onStateChange(int[] stateSet) {
          final boolean changed = super.onStateChange(stateSet);
          int idx = mAnimationScaleListState.getCurrentDrawableIndexBasedOnScale();
          return selectDrawable(idx) || changed;
      }
docs: Set the current drawable according to the animation scale. If scale is 0, then pick the
  static drawable, otherwise, pick the animatable drawable.