code: public final boolean isLoading() {
          if (mDatas.isEmpty()) {
              return false;
          }
          for (int i = 0; i < mDatas.size(); i++) {
              if (mDatas.get(i).isLoading()) {
                  return true;
              }
          }
          return false;
      }
docs: Returns if any of the observed {@link Data} instances are loading.