protected function getRowValues($columns, $model, $index = 0)
    {
        $values = [];
        $keys = $this->dataProvider->getKeys();
        foreach ($columns as $column) {
            /** @var \kartik\grid\DataColumn $column */
            if ($column instanceof DataColumn) { // we only work with DataColumn types
                $values[$column->attribute] = $this->getColumnDataCellContent($column, $model, $keys[$index], $index);
            }
        }

        return $values;
    }