使用QPainter将QPrinter打印为PDF时会崩溃

Question

我正在使用类QPrinter和QPainter打印成PDF文件与一个Windows虚拟设备。QPainter对象打开一个对话框窗口，在该窗口中可以介绍PDF文件的路径和名称。

它对有意使用是正确的。但是，当按下对话框中的“取消”按钮时，应用程序就会崩溃。下面是一个复制错误的代码片段：

#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;
}

通过按下Cancel按钮，应用程序在调用QPainter::begin()时崩溃。我是不是遗漏了什么？这种方法可能有错误吗？

更新:保护对QPainter::begin()的调用的没有防止崩溃：

#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

尝试使用QPrinter::ScreenResolution而不是QPrinter::HighResolution。

PDF打印机设置1200 dpi导致了500 MB的内存分配，这对于32位Qt来说太多了，因此崩溃的原因是来自QImage的malloc。

或者，您可以切换到64位Qt。它仍然是缓慢的，但打印很好。如果您想要比ScreenResolution更高的dpi，可以使用QPrinter::setResolution(int dpi)将其设置为300左右。