Qt6.24 QPrintPreViewDialog issues

[Sam1990]

hi ,
i used IED Qt6.24 to design a function that display file preview with QPrintPreViewDialog widget,it previewed nothing,it's so weirod,codes showed below:
void MainWindow::on_ActionPrintView_Clicked(void)
{
QPrinter printer;

printer.setPageSize(QPageSize::A4);
printer.setFullPage(true);
//printer.setOutputFormat(QPrinter::NativeFormat);
printer.setPageOrientation(QPageLayout::Portrait);
//QMarginsF pageMargins(20,20,20,20);
//printer.setPageMargins(pageMargins,QPageLayout::Millimeter);

QPrintPreviewDialog preview(&printer,this,Qt::Window);
preview.showNormal();
connect(&preview,&QPrintPreviewDialog::paintRequested,this,&MainWindow::previewPaint);
preview.exec();

}
void MainWindow::previewPaint(QPrinter *printer)
{

qDebug()<<"you clicked preview button!";
//QPainter p(printer);
//p.setRenderHints(QPainter::Antialiasing|QPainter::TextAntialiasing|QPainter::SmoothPixmapTransform,true);
//printer->newPage();
QCPDocumentObject *plotObjectHandler=new QCPDocumentObject(this);
QTextCursor cursor;
QTextDocument doc;
doc.documentLayout()->registerHandler(QCPDocumentObject::PlotTextFormat,plotObjectHandler);
cursor.insertText(QString(QChar::ObjectReplacementCharacter), QCPDocumentObject::generatePlotFormat(ui->plot, ui->plot->width(), ui->plot->height()));

doc.print(printer);

//p.drawText(20,20,"textdoc.toPlainText()");

}