protected function _getHeader()
    {
        $header = [];
        foreach ($this->_grid->getColumns() as $column) {
            if ($column instanceof Column\IndexColumn || $column instanceof Column\OperationColumn) {
                continue;
            }
            if ($column instanceof Column\CustomColumn && !$column->getExporting()) {
                continue;
            }
            $header[] = $column->getLabel();
        }
        return $header;
    }