code: private void doOnLongFocus() {
          final List<OnFocusListener> focusListeners;
          synchronized (mFocusListeners) {
              focusListeners = new ArrayList<>(mFocusListeners);
          }
  
          for (OnFocusListener listener : focusListeners) {
              if (listener.onLongFocus(this)) {
                  return;
              }
          }
          onLongFocus();
          final boolean inFollowFocusGroup = isInFollowFocusGroup();
          for (Widget child : getChildren()) {
              if (child.mFocusEnabled
                      && (mChildrenFollowFocus || child.mFollowParentFocus || inFollowFocusGroup)) {
                  child.doOnLongFocus();
              }
          }
      }
docs: Called when this {@link Widget} has had line-of-sight focus for more than
  {@link #getLongFocusTimeout()} milliseconds. Notifies all
  {@linkplain OnFocusListener#onLongFocus() listeners}; if none of the
  listeners has completely handled the event, {@link #onLongFocus()} is
  called.