WebEngine Widgets Html2Pdf Example | Qt WebEngine 5.9

Qt 5.9 | Qt WebEngine | Qt WebEngine Widgets Examples | WebEngine Widgets Html2Pdf Example

Qt 5.9.9 Reference Documentation

# WebEngine Widgets Html2Pdf Example

Html2Pdf demonstrates how to use Qt WebEngine to implement a command-line application for converting web pages into PDF documents.

## Running the Example

To run the example from Qt Creator, open the Welcome mode and select the example from Examples. For more information, visit Building and Running an Example.

## The Conversion Process

In order to convert a web page into a PDF document we need to:

1. Create a QWebEnginePage.
2. Tell the QWebEnginePage to begin loading the target URL and wait for it to finish.
3. Tell the QWebEnginePage to begin converting the loaded page into a PDF file and again wait for it to finish.
4. Once the conversion is finished, exit the program.

This process is encapsulated in the Html2PdfConverter class:

      #include <QApplication>
      #include <QCommandLineParser>
      #include <QFile>
      #include <QTextStream>
      #include <QWebEnginePage>

      #include <functional>

      using namespace std;
      using namespace std::placeholders;

      class Html2PdfConverter : public QObject
      {
          Q_OBJECT
      public:
          explicit Html2PdfConverter(QString inputPath, QString outputPath);
          int run();

      private slots:
          void loadFinished(bool ok);
          void pdfPrintingFinished(const QString &filePath, bool success);

      private:
          QString m_inputPath;
          QString m_outputPath;
          QScopedPointer<QWebEnginePage> m_page;
      };

In the constructor we create the QWebEnginePage and connect to its QWebEnginePage::loadFinished and QWebEnginePage::pdfPrintingFinished signals:

      Html2PdfConverter::Html2PdfConverter(QString inputPath, QString outputPath)
          : m_inputPath(move(inputPath))
          , m_outputPath(move(outputPath))
          , m_page(new QWebEnginePage)
      {
          connect(m_page.data(), &QWebEnginePage::loadFinished,
                  this, &Html2PdfConverter::loadFinished);
          connect(m_page.data(), &QWebEnginePage::pdfPrintingFinished,
                  this, &Html2PdfConverter::pdfPrintingFinished);
      }

The `run()` method will trigger the conversion process by asking QWebEnginePage to start loading the target URL. We then enter the main event loop:

      int Html2PdfConverter::run()
      {
          m_page->load(QUrl::fromUserInput(m_inputPath));
          return QApplication::exec();
      }

After the loading is finished we begin PDF generation. We ask the QWebEnginePage::printToPdf method to write the output directly to disk:

      void Html2PdfConverter::loadFinished(bool ok)
      {
          if (!ok) {
              QTextStream(stderr)
                  << tr("failed to load URL '%1'").arg(m_inputPath) << "\n";
              QCoreApplication::exit(1);
              return;
          }

          m_page->printToPdf(m_outputPath);
      }

Once we receive the signal that the PDF conversion has finished, all that remains is to report potential errors and exit the program:

      void Html2PdfConverter::pdfPrintingFinished(const QString &filePath, bool success)
      {
          if (!success) {
              QTextStream(stderr)
                  << tr("failed to print to output file '%1'").arg(filePath) << "\n";
              QCoreApplication::exit(1);
          } else {
              QCoreApplication::quit();
          }
      }

## The Main Function

Our `main` function is responsible for setting up a QApplication and parsing command line arguments:

      int main(int argc, char *argv[])
      {
          QApplication app(argc, argv);
          QCoreApplication::setApplicationName("html2pdf");
          QCoreApplication::setApplicationVersion(QT_VERSION_STR);

          QCommandLineParser parser;
          parser.setApplicationDescription(
              QCoreApplication::translate("main", "Converts the web page INPUT into the PDF file OUTPUT."));
          parser.addHelpOption();
          parser.addVersionOption();
          parser.addPositionalArgument(
              QCoreApplication::translate("main", "INPUT"),
              QCoreApplication::translate("main", "Input URL for PDF conversion."));
          parser.addPositionalArgument(
              QCoreApplication::translate("main", "OUTPUT"),
              QCoreApplication::translate("main", "Output file name for PDF conversion."));

          parser.process(QCoreApplication::arguments());

          const QStringList requiredArguments = parser.positionalArguments();
          if (requiredArguments.size() != 2)
              parser.showHelp(1);

          Html2PdfConverter converter(requiredArguments.at(0), requiredArguments.at(1));
          return converter.run();
      }

Note that to use Qt WebEngine Widgets we need to create a QApplication and not a QCoreApplication, even though this is a command line application.

Files:

- webenginewidgets/html2pdf/html2pdf.cpp
- webenginewidgets/html2pdf/html2pdf.pro