code: def on_activity_add_clicked(self, button):
          
          category_id = self._get_selected_category()
  
          new_activity = self.activity_store.append([-1, _("New activity"), category_id])
  
          (model, iter) = self.selection.get_selected()
  
          self.activityCell.set_property("editable", True)
          self.activity_tree.set_cursor_on_cell(model.get_path(new_activity),
                                                focus_column = self.activity_tree.get_column(0),
                                                focus_cell = None,
                                                start_editing = True)
docs: appends row, jumps to it and allows user to input name