Affecting a QDialog From A QThread

Question

I would like to affect a QDialog from a separate thread, I have to do two things:

dialog->show();
dialog->raise();
dialog->activateWindow();

As far as I understand, these are events and thus MUST be done in the main thread event loop. I think I achieve this with QApplication::postEvent within in the QThread::run(). Could anyone confirm?

Second, I would like to display an image which was processed in that separate thread. I think I need to subclass my dialog class and write a thread safe setImage() function, which is then called by paintEvent()... However, this seems like it's impossible. I can't block the paintEvent with a QMutex::unlock()? Could anyone offer some suggestions?

---

QApplication::postEvent(dialog, new QShowEvent()); did not work.

This is the solution for calling slots (as functions) from a seperate thread:

QMetaObject::invokeMethod(dialog, "show", Qt::QueuedConnection);
QMetaObject::invokeMethod(dialog, "raise", Qt::QueuedConnection);

... Still working on activateWindow() and QThread safe functions.

So for the QImage, it is a QPaintDevice. Supposedly it is thread safe. My approach would've been to have a class member QImage that is set within the thread. Then painted later.

Note, that the below approach is as good, if not better though.

Answer 1

I think this is a clearer way to do what you want:

class Dialog : public QDialog
{
    ...
public slots:
    void showImage(QImage img);
    ...
}

void Dialog::showImage(QImage img);
{
    setImage(img);
    show();
    raise();
    activateWindow();
}

class Thread : public QThread
{
    ...
signals:
    void imageReady(QImage);
}

void Thread::run()
{
    QImage img;
    /// image processing stuff

    emit imageReady(img);
    ...
}


Thread *thread = new Thread;
Dialog *dialog = new Dialog;
connect(thread, SIGNAL(imageReady(QImage)), dialog, SLOT(showImage(QImage)));

thread->start();