Error with FPDF - php

Question

I don't know why but my pdf batch does'nt work and now I have this error.
The problem come from the class inside the while loop
Thank you
Notice: OM\Registry::set - Order already registered and is not forced to be replaced in /home/www/shop/includes/OM/Registry.php on line 33
Fatal error: Uncaught Exception: FPDF error: Some data has already been output, can't send PDF file in /home/www/boutique/ext/fpdf/fpdf.php:271 Stack trace: #0 /home/www/boutique/ext/fpdf/fpdf.php(1063): FPDF->Error('Some data has a...') #1 /home/www/boutique/ext/fpdf/fpdf.php(999): FPDF->_checkoutput() #2 /home/www/boutique/admin/invoice_batch.php(570): FPDF->Output() #3 {main} thrown in /home/www/boutique/ext/fpdf/fpdf.php on line 271
This error is in relation with this element
// Classe pdf.php
$pdf = new \FPDF();
// $pdf->SetWidths(array(30,50,30,40));
while ($QordersInfo->fetch()) {
Registry::set('Order', new OrderAdmin($QordersInfo->valueInt('orders_id')));
$order = Registry::get('Order');
...
..
}
// PDF's created no
// output the file
$pdf->Output();
If I write this it "works perfectly" but it display only 1 invoice.
// Classe pdf.php
$pdf = new \FPDF();
// $pdf->SetWidths(array(30,50,30,40));
while ($QordersInfo->fetch()) {
Registry::set('Order', new OrderAdmin($QordersInfo->valueInt('orders_id')));
$order = Registry::get('Order');
.....
// output the file
$pdf->Output();
}

Answer 1

It is difficult to trace the problem without knowing what Registry::set() does, but it looks like the first parameter of that function should be a unique key. In your code the key is always 'Order' in every iteration of the loop. The first iteration will be fine, but in the second iteration it will generate output to give you a Notice that there already is a Registry entry with that key.
The $pdf->Output() function checks to see if anything in your PHP code has already produced any output. Because the Notice was sent to output, FPDF cannot start rendering and produces the FPDF error to let you know.
Either use a unique key (perhaps the ID of the order?) or force the Registry entry to be replaced in every iteration. If that does not get you on track again, post the Registry class code so we can delve deeper into the problem.