QMessageBox in initializeGL calls initializeGL one more time

[DIMEDROLL]

void MyGlWidget::initializeGL() {
    try {
        throw std::exception();
    } catch(...) {        
        QMessageBox::critical(this, tr("Exception"), 
            tr("Exception occured"));
    }    
}

void MyGlWidget::initializeGL() {
    try {
        throw std::exception();
    } catch(...) {        
        QMessageBox::critical(this, tr("Exception"), 
            tr("Exception occured"));
    }    
}

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in catch() messagebox is shown and execution goes into initializeGL() again, and shows a second message box

I'm trying to avoid this via a bool variable:

void MyGlWidget::initializeGL() {
    if(in_initializeGL_)
        return;
    in_initializeGL_ = true;
 
    try {
        throw std::exception();
    } catch(...) {        
        QMessageBox::critical(this, tr("Exception"), 
        tr("Exception occured"));
    }
 
    in_initializeGL_ = false;
}

void MyGlWidget::initializeGL() {
    if(in_initializeGL_)
        return;
    in_initializeGL_ = true;

    try {
        throw std::exception();
    } catch(...) {        
        QMessageBox::critical(this, tr("Exception"), 
        tr("Exception occured"));
    }

    in_initializeGL_ = false;
}

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But this leads to crash. So I decided to show error in paintGL()(it also shows 2 messageboxes):

void MyGlWidget::paintGL() {
    if(in_paintGL_)
        return;
    in_paintGL_ = true;
 
    if (!exception_msg_.isEmpty()) {
        QMessageBox::critical(this, tr("Exception"), 
            exception_msg_);
        exception_msg_.clear();
    }
 
    // rendering stuff 
 
    in_paintGL_ = false;
}
 
void MyGlWidget::initializeGL() {
    try {
        throw std::exception();            
    } catch(...) {        
        exception_msg_ = "Exception in initializeGL()";
    }
}

void MyGlWidget::paintGL() {
    if(in_paintGL_)
        return;
    in_paintGL_ = true;

    if (!exception_msg_.isEmpty()) {
        QMessageBox::critical(this, tr("Exception"), 
            exception_msg_);
        exception_msg_.clear();
    }

    // rendering stuff 

    in_paintGL_ = false;
}

void MyGlWidget::initializeGL() {
    try {
        throw std::exception();            
    } catch(...) {        
        exception_msg_ = "Exception in initializeGL()";
    }
}

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This solves the problem but the code is ugly. Is there a more nice solution of this problem?

[high_flyer]

Does this double showing of QMessageBox also happens when you construct the messagebox with a NULL parent?

[DIMEDROLL]

Yes.
The call stack is(from down to up):
...
initializeGL()
updateGL()
QMessageBox::critical()
initializeGL()

[high_flyer]

hmm... my guess is that it has to do with QMessageBox showing it self, while you are in a paintEvent() - that maybe forces a general paintEvent() on all the applications visible widgets, resulting in a recursive call.
But that is only a guess.

[franz]

Opening the QMessageBox using one of the static functions starts a new event loop. This is an Unpredictable exec() issue.

[DIMEDROLL]

Thanks! Nice article and solution.

void MyGlWidget::initializeGL() {
    try {
        throw std::exception();        
    } catch(...) {        
        getExceptionMessage(&exception_msg_);
        QMessageBox *msgbox = new QMessageBox(QMessageBox::Warning, 
                                              "Exception", 
                                              exception_msg_, 
                                              QMessageBox::Ok, 
                                              this);
        msgbox->open(0, 0);
    }
}

void MyGlWidget::initializeGL() {
    try {
        throw std::exception();        
    } catch(...) {        
        getExceptionMessage(&exception_msg_);
        QMessageBox *msgbox = new QMessageBox(QMessageBox::Warning, 
                                              "Exception", 
                                              exception_msg_, 
                                              QMessageBox::Ok, 
                                              this);
        msgbox->open(0, 0);
    }
}

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Don't forget to use "new QMessageBox", because "QMessageBox msgbox;" will be deleted on scope exit. open() doesn't block the execution.