Custom Printing(PageSize) is not working properly on QPrintPreviewDialog,QPrintDialog

My OS version is Ubuntu 20.04

I want to print with custom size as Half-Letter. I 've already loaded the printer by

printer.setPaperSize( QSizeF(216,140) , QPrinter::Unit::Millimeter );

By using QPrintPreviewDialog  to preview custom size ,it seems printing preview is valid.

qDebug() << printer.pageSize(); // this return 30

But after click  print button and print to printer ,the size is not valid.

qDebug() << printer.pageSize(); // this return 0  on printing to printer

 

Without using custom size ,it works fine. Only custom size will never work.

 

I fixed my software by avoiding QPrintPreviewDialog and QPrintDialog

 

//## it works without QPrintPreviewDialog and QPrintDialog .

if ( printer.pageSize() == QPrinter::PageSize::Custom ) {

QList<QPrinterInfo> list_printer=QPrinterInfo::availablePrinters();

QStringList string_list_printer_name;
for(int i=0;i<list_printer.size();++i)
{
QPrinterInfo printer_info=list_printer.at;
string_list_printer_name << printer_info.printerName();
}
QInputDialog dialog_select_printer;

dialog_select_printer.setOptions(QInputDialog::UseListViewForComboBoxItems);
dialog_select_printer.setComboBoxItems(string_list_printer_name);
dialog_select_printer.setWindowTitle("Select Printer");
dialog_select_printer.exec();

QString printer_name=dialog_select_printer.textValue();

qDebug() << "select printer_name : " << printer_name;

printer.setPrinterName( printer_name );

QPainter painter;
painter.begin(&printer);

Render(painter);

painter.end();

{color:#00875a}}