code: private void ensureContent() {
          if (mContentContainer != null && mProgressContainer != null) {
              return;
          }
          View root = getView();
          if (root == null) {
              throw new IllegalStateException("Content view not yet created");
          }
          mProgressContainer = root.findViewById(R.id.progress_container);
          if (mProgressContainer == null) {
              throw new RuntimeException("Your content must have a ViewGroup whose id attribute is 'R.id.progress_container'");
          }
          mContentContainer = root.findViewById(R.id.content_container);
          if (mContentContainer == null) {
              throw new RuntimeException("Your content must have a ViewGroup whose id attribute is 'R.id.content_container'");
          }
          mEmptyView = root.findViewById(android.R.id.empty);
          if (mEmptyView != null) {
              mEmptyView.setVisibility(View.GONE);
          }
          mContentShown = true;
          // We are starting without a content, so assume we won't
          // have our data right away and start with the progress indicator.
          if (mContentView == null) {
              setContentShown(false, false);
          }
      }
docs: Initialization views.