Persisting / Serializing QPrinter (QPrintDialog) between execution

Question

In a Qt Desktop application, how can I persist the QPrinter selection between application runs?

Consider the following code:

printDialog = new QPrintDialog();
if (printDialog->exec() == QDialog::Accepted) {
    qDebug() << printDialog->printer(); // Gives just a pointer value,
                                        // no real use for serializing.
    view->print(printDialog->printer());
}

I'd like to be able to do both:

printDialog = new QPrintDialog("some-previously stored settings") 

and, without even invoking QPrintDialog, simply print to the pre-selected printer like that:

view->print(new QPrinter("some previously stored settings"))

There is a function that deals with QPrinterInfo, but it merely returns the printer name.. Any other suggestions?

Answer 1

I wrote the following code to read and write all available Settings of QPrinter to a QDataStream. Unfortunately this does not by far save/restore all available Printer options (i.e. on Windows). But the Printer name, Page size etc. is restored correctly.

Feel free to reuse.

    ///////////////////////////////////////////////////////////////////////////////
    // Write all available Attributes from QPrinter into stream
    ///////////////////////////////////////////////////////////////////////////////

    template <typename t> void  writeStreamElement(QDataStream &os, t param)
    {
        int i = static_cast<int>(param);
        os << i;
    }
    template <>           void writeStreamElement<QString>(QDataStream &os, QString s)
    {
        os << s;
    }

    QDataStream& operator<<(QDataStream &os, const QPrinter &printer)
    {
        writeStreamElement(os, printer.printerName         ());
        writeStreamElement(os, printer.pageSize            ());
        writeStreamElement(os, printer.collateCopies       ());
        writeStreamElement(os, printer.colorMode           ());
        writeStreamElement(os, printer.copyCount           ());
        writeStreamElement(os, printer.creator             ());
        writeStreamElement(os, printer.docName             ());
        writeStreamElement(os, printer.doubleSidedPrinting ());
        writeStreamElement(os, printer.duplex              ());
        writeStreamElement(os, printer.fontEmbeddingEnabled());
        writeStreamElement(os, printer.fullPage            ());
        writeStreamElement(os, printer.orientation         ());
        writeStreamElement(os, printer.outputFileName      ());
        writeStreamElement(os, printer.outputFormat        ());
        writeStreamElement(os, printer.pageOrder           ());
        writeStreamElement(os, printer.paperSize           ());
        writeStreamElement(os, printer.paperSource         ());
        writeStreamElement(os, printer.printProgram        ());
        writeStreamElement(os, printer.printRange          ());
        writeStreamElement(os, printer.printerName         ());
        writeStreamElement(os, printer.resolution          ());
        writeStreamElement(os, printer.winPageSize         ());

        qreal left, top, right, bottom;
        printer.getPageMargins(&left, &top, &right, &bottom, QPrinter::Millimeter);
        os << left << top << right << bottom;

        Q_ASSERT_X(os.status() == QDataStream::Ok, __FUNCTION__, QString("Stream status = %1").arg(os.status()).toStdString().c_str());
        return os;
    }
    ///////////////////////////////////////////////////////////////////////////////
    // Read all available Attributes from tream into QPrinter
    ///////////////////////////////////////////////////////////////////////////////


    template <typename t> t readStreamElement(QDataStream &is)
    {
        int i;
        is >> i;
        return static_cast<t>(i);
    }
    template <> QString readStreamElement<QString>(QDataStream &is)
    {
        QString s;
        is >> s;
        return s;
    }

    QDataStream& operator>>(QDataStream &is,  QPrinter &printer)
    {

        printer.setPrinterName              (readStreamElement<QString>                (is));
        printer.setPageSize                 (readStreamElement<QPrinter::PaperSize>    (is));
        printer.setCollateCopies            (readStreamElement<bool>                   (is));
        printer.setColorMode                (readStreamElement<QPrinter::ColorMode>    (is));
        printer.setCopyCount                (readStreamElement<int>                    (is));
        printer.setCreator                  (readStreamElement<QString>                (is));
        printer.setDocName                  (readStreamElement<QString>                (is));
        printer.setDoubleSidedPrinting      (readStreamElement<bool>                   (is));
        printer.setDuplex                   (readStreamElement<QPrinter::DuplexMode>   (is));
        printer.setFontEmbeddingEnabled     (readStreamElement<bool>                   (is));
        printer.setFullPage                 (readStreamElement<bool>                   (is));
        printer.setOrientation              (readStreamElement<QPrinter::Orientation>  (is));
        printer.setOutputFileName           (readStreamElement< QString >              (is));
        printer.setOutputFormat             (readStreamElement<QPrinter::OutputFormat> (is));
        printer.setPageOrder                (readStreamElement<QPrinter::PageOrder>    (is));
        printer.setPaperSize                (readStreamElement<QPrinter::PaperSize>    (is));
        printer.setPaperSource              (readStreamElement<QPrinter::PaperSource>  (is));
        printer.setPrintProgram             (readStreamElement<QString>                (is));
        printer.setPrintRange               (readStreamElement<QPrinter::PrintRange>   (is));
        printer.setPrinterName              (readStreamElement<QString>                (is));
        printer.setResolution               (readStreamElement<int>                    (is));
        printer.setWinPageSize              (readStreamElement<int>                    (is));

        qreal left, top, right, bottom;
        is >> left >> top >> right >> bottom;

        printer.setPageMargins(left, top, right, bottom, QPrinter::Millimeter);

        Q_ASSERT_X(is.status() == QDataStream::Ok, __FUNCTION__, QString("Stream status = %1").arg(is.status()).toStdString().c_str());

        return is;
    }


    ///////////////////////////////////////////////////////////////////////////////
    // persist settings
    ///////////////////////////////////////////////////////////////////////////////
    QPrinter *sgPrinter =...;
...
    QByteArray byteArr;
    QDataStream os(&byteArr, QIODevice::WriteOnly);
    os << *sgPrinter;
    QSettings settings("justMe", "myApp"));
    settings.setValue("printerSetup", byteArr.toHex());

    ///////////////////////////////////////////////////////////////////////////////
    // restore settings
    ///////////////////////////////////////////////////////////////////////////////
    QByteArray printSetUp = settings.value("printerSetup").toByteArray();
    printSetUp = QByteArray::fromHex(printSetUp);
    QDataStream is(&printSetUp, QIODevice::ReadOnly);
    is >> *sgPrinter;

Answer 2

You have been left out in the cold by Qt. The feature you are asking for is not available. Related Qt feature requests (observe the age and priority of the requests):

QPrinter: add << and >> operators so that the settings can be saved and loaded

QPrinter should provide a way to store/restore the settings

As of the current Qt version, you must save/load relevant QPrintDialog and QPrinter values to QSettings (or such, serializable to a file) manually. Guessing from the last helpful comment in both mentioned QTBUGs, there is no improvement in Qt 5.0.