[SOLVED] Accessing UI from QtConcurrent::run

Chick3nN00dleS0up

In my "DelayedRespondingBlock" I try to execute a method delayed without delaying the whole application, so I multithread and make the new thread sleeping for a little time:

void DelayedRespondingBlock::updateOutputs() //called from another class
{
    QFuture<void> future = QtConcurrent::run(this, &DelayedRespondingBlock::doUpdateOutputs);
}

void DelayedRespondingBlock::doUpdateOutputs()
{
    #ifdef Q_OS_WIN
        Sleep(uint(delay_ms));
    #else
        struct timespec ts = { delay_ms / 1000, (delay_ms % 1000) * 1000 * 1000 };
        nanosleep(&ts, NULL);
    #endif

    this->produceOutputValues();
}

This code works perfectly.
I derive "LedBlock" from DelayedRespondingBlock and implement produceOutputValues():

void LedBlock::produceOutputValues()
{
    this->repaint(); //paintEvent() checks some booleans
}

delay_ms is 1000 for LedBlock.
After those 1000 ms, produceOutputValues() is called, so this->repaint() is called and the QWidget-class does some stuff, and finally my paintEvent() is called:

void LedBlock::paintEvent(QPaintEvent *event)
{
    QPainter* painter = new QPainter(this);
    painter->eraseRect(QRect(QPoint(0,0), QPoint(this->size().width(), this->size().height())));
    if(this->getInputSockets().at(0)->getValue() == true)
    {
        painter->setBrush(QBrush(this->illuminationColor,Qt::SolidPattern));
        painter->drawEllipse(QRect(10, 1, 18, 18));
    }
    painter->setPen(QPen(this->getColor(), 2, Qt::SolidLine, Qt::SquareCap));
    painter->drawEllipse(QRect(10, 1, 18, 18));
    painter->end();
}

There are some more steps after my paintEvent is finished, but after that, I crash.
How am able to repaint my Widget from another Thread, without making it crash? Thanks in advance!

? Offline

Hi,
painting can only be done in the GUI thread. You could send a Qt signal from your worker thread to the GUI thread to trigger the repaint (signals/slots are thread safe).

Chick3nN00dleS0up

@Wieland Thank you, it worked! :)

? Offline

@Chick3nN00dleS0up You're welcome :-)