PHPSpreadsheet - can't update an existing spreadsheet but can write to new spreadsheet?

Question

so I'm using PHPSpreadsheet to write to an existing spreadsheet but for some reason I keep getting this error:

PHP Fatal error:  Uncaught Error: Call to a member function setValue() on null in /home/joe/vendor/phpoffice/phpspreadsheet/samples/vendor/phpoffice/phpspreadsheet/src/PhpSpreadsheet/Worksheet/Worksheet.php:1127
Stack trace:
#0 /home/joe/vendor/phpoffice/phpspreadsheet/samples/server.php(90): PhpOffice\PhpSpreadsheet\Worksheet\Worksheet->setCellValue('b15', '6429093')
#1 {main}
  thrown in /home/joe/vendor/phpoffice/phpspreadsheet/samples/vendor/phpoffice/phpspreadsheet/src/PhpSpreadsheet/Worksheet/Worksheet.php on line 1127

I only get this error when trying to load from an existing spreadsheet and not when loading from a new spreadsheet. Code is as follows:

$spreadsheet = new Spreadsheet();
$sheet = $spreadsheet->getActiveSheet();
$letters = ['a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z','aa','ab','ac','ad','ae','af','ag','ah','ai','aj','ak','al','am','an','ao','ap','aq','ar','as','at','au','av','aw','ax','ay','az','ba','bb','bc','bd','be'];

    $numColumns = count($letters);

    foreach($rows as $row) {

        foreach($row as $key => $value) {

            if(isset($value) && $value != null) {

                $sheet->setCellValue($letters[$key].$i, $value);
            }

            //print_r();
        }

        $i++;
    }

The spreadsheet that I'm loading from just contains a bunch of cell formatting and some cells that already have data in. Any help you could offer would be great :-)

Answer 1

Letters should be uppercases, not lowercase, this method is to get char by ascii code. And convert that in to get it's char with function chr .

ascii code.
chr php function

$letters = range(65, 90) // A-Z ascii code

foreach($rows as $i => $row) {

   foreach($row as $j => $value) {

     if(isset($value) && $value != null) {

        // array start from 0, but spreadsheet line start from 1. then $i+1  
        $sheet->setCellValue( chr($letters[$j]).($i+1) , $value); // A1, $value
     }

     //print_r();
   }
 }