PHPExcel 修改已经存在的excel文档中某个sheet中的内容

<?php
error_reporting(E_ALL &~ E_WARNING &~ E_NOTICE);
date_default_timezone_set('Europe/London');
require_once './Classes/PHPExcel/IOFactory.php';
$filePath = './SR_Template.xlsx';
//读取文件
    if (!file_exists($filePath)) {
        exit("you dont have ");
    }else{
    }
$connection = @mysql_connect("localhost:3306","root","111111");
mysql_select_db("sr_template", $connection);
    if (!$connection)
    {
        die('Could not connect: ' . mysql_error());
    }
mysql_close($con);
$objPHPExcel = PHPExcel_IOFactory::load($filePath);
$sheet = $objPHPExcel->getSheet(0); // 读取第一��工作表
$highestColumm = $sheet->getHighestColumn(); // 取得总列数
$highestRow = $sheet->getHighestRow(); // 取得总行数
$exlCASArr = array();
/** 循环读取每个单元格的数据 */
for ($row =2; $row <= $highestRow; $row++){//行数是以第1行开始
    $ex = $sheet->getCell('E'.$row)->getValue();
    $sql = 'select a,b from table where ex='.$ex;//和数据
    $resultInfo = mysql_query($sql,$connection);
    $casInfo = mysql_fetch_array($resultInfo); 
    //这里这样写有报错
    /*
    $objPHPExcel->setActiveSheetIndex(0)
    ->setCellValue('G'.$row, $casInfo['a']);
    ->setCellValue('H'.$row, $casInfo['b']);
    */
    $objPHPExcel->setActiveSheetIndex(0)
    ->setCellValue('G'.$row, $casInfo['a']);//修改数据
    $objPHPExcel->setActiveSheetIndex(0)
    ->setCellValue('H'.$row, $casInfo['b']);
}
// Rename worksheet
$objPHPExcel->getActiveSheet()->setTitle('Simple');
// Set active sheet index to the first sheet, so Excel opens this as the first sheet
$objPHPExcel->setActiveSheetIndex(0);
// Redirect output to a client’s web browser (Excel5)
header('Content-Type: application/vnd.ms-excel');
header('Content-Disposition: attachment;filename="01simple.xlsx"');
header('Cache-Control: max-age=0');
// If you're serving to IE 9, then the following may be needed
header('Cache-Control: max-age=1');
// If you're serving to IE over SSL, then the following may be needed
header ('Expires: Mon, 26 Jul 1997 05:00:00 GMT'); // Date in the past
header ('Last-Modified: '.gmdate('D, d M Y H:i:s').' GMT'); // always modified
header ('Cache-Control: cache, must-revalidate'); // HTTP/1.1
header ('Pragma: public'); // HTTP/1.0
$objWriter = PHPExcel_IOFactory::createWriter($objPHPExcel, 'Excel2007');
$objWriter->save('文件路径\\01simple.xlsx');
exit;
?>