kartik\export\ExportMenu::generateFooter PHP Method

    public function generateFooter()
    {
        $row = $this->_endRow + $this->_beginRow;
        $footerExists = false;
        $columns = $this->getVisibleColumns();
        if (count($columns) == 0) {
            return;
        }
        $this->_endCol = 0;
        foreach ($this->getVisibleColumns() as $n => $column) {
            $this->_endCol = $this->_endCol + 1;
            if ($column->footer) {
                $footerExists = true;
                $footer = trim($column->footer) !== '' ? $column->footer : $column->grid->blankDisplay;
                $cell = $this->_objPHPExcel->getActiveSheet()->setCellValue(self::columnName($this->_endCol) . ($row + 1), $footer, true);
                $this->raiseEvent('onRenderFooterCell', [$cell, $footer, $this]);
            }
        }
        if ($footerExists) {
            $row++;
        }
        return $row;
    }