Qt 5.11 | Qt Concurrent | QtConcurrent Progress Dialog Example | main.cpp Example File

Qt 5.11.3 Reference Documentation

# main.cpp Example File

progressdialog/main.cpp

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      #include <QtWidgets>
      #include <QtConcurrent>

      #include <functional>

      using namespace QtConcurrent;

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

          const int iterations = 20;

          // 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, &QFutureWatcher<void>::finished, &dialog, &QProgressDialog::reset);
          QObject::connect(&dialog, &QProgressDialog::canceled, &futureWatcher, &QFutureWatcher<void>::cancel);
          QObject::connect(&futureWatcher,  &QFutureWatcher<void>::progressRangeChanged, &dialog, &QProgressDialog::setRange);
          QObject::connect(&futureWatcher, &QFutureWatcher<void>::progressValueChanged,  &dialog, &QProgressDialog::setValue);

          // Our function to compute
          std::function<void(int&)> 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();
          };

          // 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();
      }