public function getWidget($column_id, $row_identifier, $widget_id = null)
    {
        if (isset($this->input_cells[$column_id])) {
            return $this->input_cells[$column_id]->getWidget(
                $row_identifier,
                $widget_id
            );
        }

        throw new SwatException(
            'No input cell for this row exists for the ' .
                'given column identifier.'
        );
    }