Qt 5.6 | Qt Concurrent | QtConcurrent Progress Dialog Example | main.cpp Example File

Qt 5.6.2 Reference Documentation

# main.cpp Example File

progressdialog/main.cpp

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      #include <QtWidgets>
      #include <QtConcurrent>

      using namespace QtConcurrent;

      const int iterations = 20;

      void spin(int &iteration)
      {
          const int work = 1000 * 1000 * 40;
          volatile int v = 0;
          for (int j = 0; j < work; ++j)
              ++v;

          qDebug() << "iteration" << iteration << "in thread" << QThread::currentThreadId();
      }

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

          // Prepare the vector.
          QVector<int> vector;
          for (int i = 0; i < iterations; ++i)
              vector.append(i);

          // Create a progress dialog.
          QProgressDialog dialog;
          dialog.setLabelText(QString("Progressing using %1 thread(s)...").arg(QThread::idealThreadCount()));

          // Create a QFutureWatcher and connect signals and slots.
          QFutureWatcher<void> futureWatcher;
          QObject::connect(&futureWatcher, SIGNAL(finished()), &dialog, SLOT(reset()));
          QObject::connect(&dialog, SIGNAL(canceled()), &futureWatcher, SLOT(cancel()));
          QObject::connect(&futureWatcher, SIGNAL(progressRangeChanged(int,int)), &dialog, SLOT(setRange(int,int)));
          QObject::connect(&futureWatcher, SIGNAL(progressValueChanged(int)), &dialog, SLOT(setValue(int)));

          // Start the computation.
          futureWatcher.setFuture(QtConcurrent::map(vector, spin));

          // Display the dialog and start the event loop.
          dialog.exec();

          futureWatcher.waitForFinished();

          // Query the future to check if was canceled.
          qDebug() << "Canceled?" << futureWatcher.future().isCanceled();
      }