code: def set_current_index(self, index):
          
          # d = self.declaration
          # #: We have to wait for the current_index to be ready before we can
          # #: change pages
          if self._notify_count > 0:
              self._pending_calls.append(
                  lambda index=index: self.widget.setCurrentItem(index))
          else:
              self.widget.setCurrentItem(index)
docs: We can only set the index once the page has been created.
          otherwise we get `FragmentManager is already executing transactions`
          errors in Java. To avoid this, we only call this once has been loaded.