code: protected void setLoadingDrawable(LoadingDrawable drawable) {
          if (drawable == null) {
              throw new NullPointerException("LoadingDrawable is null, You can only set the STYLE_CIRCLE and STYLE_LINE parameters.");
          } else {
              drawable.setCallback(this);
              mLoadingDrawable = drawable;
  
              invalidate();
              requestLayout();
          }
      }
docs: In this we set LoadingDrawable really
  
  @param drawable {@link LoadingDrawable}