Qt4 starting and stopping (pausing)

Question

Ok, so I'm having this problem tonight:

[...]   

connect(startButton, SIGNAL(clicked()), this, SLOT(startCalculation()));
connect(stopButton, SIGNAL(clicked()), this, SLOT(stopCalculation()));

[...]

void MainWindow::startCalculation()
{
   qDebug() << "hello";
   this->startButton->setDisabled(true);
   this->stopButton->setEnabled(true);
   this->calcStatus = true;
   this->calculate();
}

void MainWindow::stopCalculation()
{
    this->startButton->setEnabled(true);
    this->stopButton->setDisabled(true);
    this->calcStatus = false;
}


void MainWindow::calculate()
{
   qDebug() << "hello";
   while(this->calcStatus)
   {
   }
}
[...]

I'm trying to make the calculate() procedure stoppable any time, but right after it is started I loose control and I can't press STOP. Of course in my future plans calculate() is going to "calculate" something real (e.g. heat transfer simulation).

Thanks for suggestions. P.

Answer 1

You would need to look into threading. The calculation locks the ui.

Answer 2

Well, in "Introduction to Design Patterns in C++ with Qt4" they say that

"it is possible to avoid the use of threads in favor of the Qt Event Loop combined with QTimers"

but I've never tried it :)

Actually, I've just tried -

add:

QTimer      *Timer;

in MainWindow class header and in MainWindow constructor add:

Timer = new QTimer(this);

then change calculate() from function to a signal and modify:

void MainWindow::startCalculation()
{
    qDebug() << "hello";
    this->startButton->setDisabled(true);
    this->stopButton->setEnabled(true);
    this->calcStatus = true;
    connect(Timer, SIGNAL(timeout()), this, SLOT(calculate()));
    Timer->start(0);
}

void MainWindow::stopCalculation()
{
    this->startButton->setEnabled(true);
    this->stopButton->setDisabled(true);
    this->calcStatus = false;
    Timer->stop();
    Timer->disconnect(this,SLOT(calculate()));
}

This should work as long as you dont pass any arguments into calculate().

Answer 3

I don't get pkajak's answer. Andrei is correct. You need to look into threading.