code: public @Nullable Drawable setCurrent(@Nullable Drawable newDelegate) {
      Drawable previousDelegate = setCurrentWithoutInvalidate(newDelegate);
      invalidateSelf();
      return previousDelegate;
    }
docs: Sets a new drawable to be the delegate, and returns the old one (or null).
  
  <p>This method will cause the drawable to be invalidated.
  
  @param newDelegate
  @return the previous delegate