使用QPrinter打印到PDF時QPainter崩潰

Question

我使用QPrinter和QPainter類打印到帶有Windows虛擬設備的PDF文件。 QPainter對象打開一個對話窗口，可以在其中引入PDF文件的路徑和名稱。

它適用於有意使用。 但是，在對話框中按“ 取消”按鈕時，應用程序崩潰。 這是一個復制錯誤的代碼片段：

#include <iostream>
#include <QApplication>
#include <QPrinterInfo>
#include <QPainter>

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);

    foreach(QPrinterInfo printerInfo, QPrinterInfo::availablePrinters()) {
        if (printerInfo.state() == QPrinter::PrinterState::Error)
            continue;

        // Look for the virtual printer device that generates a pdf.
        if (printerInfo.printerName() == "Microsoft Print to PDF")
        {
            QPrinter * qPrinter = new QPrinter(printerInfo, QPrinter::HighResolution);
            QPainter * qPainter = new QPainter();

            // This statement pops up a file selection dialog.
            // When it is cancelled, the application crashes ...
            qPainter->begin(qPrinter);

            // ... and this statement is never reached.
            std::cout << "Starting printing on the pdf file." << std::endl;

            // We print some text in the PDF file.
            qPainter->drawText(100, 100, "Lorem ipsum dolor sit amet, consectetur adipiscing elit.");
            qPrinter->newPage();
            qPainter->drawText(100, 100, "Mauris ut urna eget dui eleifend placerat.");
            qPrinter->newPage();

            // Close the printer and clean-up.
            qPainter->end();
            delete qPrinter;
            delete qPainter;
        }
    }

    return 0;
}

通過按“ 取消”按鈕，應用程序在調用QPainter :: begin（）期間崩潰。 我錯過了什么嗎？ 該方法可能存在錯誤嗎？

更新：使用try-catch保護對QPainter :: begin（）的調用並不能防止崩潰：

#include <iostream>
#include <QApplication>
#include <QPrinterInfo>
#include <QPainter>

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);

    foreach(QPrinterInfo printerInfo, QPrinterInfo::availablePrinters()) {
        if (printerInfo.state() == QPrinter::PrinterState::Error)
            continue;

        // Look for the virtual printer device that generates a pdf.
        if (printerInfo.printerName() == "Microsoft Print to PDF")
        {
            QPrinter * qPrinter = new QPrinter(printerInfo, QPrinter::HighResolution);
            QPainter * qPainter = new QPainter();

            // This statement pops up a file selection dialog.
            // When it is cancelled, the application crashes ...
            try
            {
                qPainter->begin(qPrinter);
            }
            catch(...) { }

            // ... and this statement is never reached.
            std::cout << "Starting printing on the pdf file." << std::endl;

            if (qPainter->isActive())
            {
                // We print some text in the PDF file.
                qPainter->drawText(100, 100, "Lorem ipsum dolor sit amet, consectetur adipiscing elit.");
                qPrinter->newPage();
                qPainter->drawText(100, 100, "Mauris ut urna eget dui eleifend placerat.");
                qPrinter->newPage();
                qPainter->end();
            }

            // Close the printer and clean-up.
            delete qPrinter;
            delete qPainter;
        }
    }

    return 0;
}

Answer 1

嘗試使用QPrinter::ScreenResolution代替QPrinter::HighResolution 。

PDF打印機設置1200 dpi ，這導致500 MB內存分配，32位Qt太多，然后崩潰來自QImage的malloc。

或者，您可以切換到64位Qt。 它仍然會很慢，但打印很好。 如果你想要比ScreenResolution更高的dpi，你可以使用QPrinter::setResolution(int dpi)將其設置為300。