QMessageBox crash when using QStyle::drawControl somewhere else

[Kampfgnom]

I have an odd problem.

I am using QStyle's drawControl() to draw a progress bar in a custom QStyledItemDelegate's paint().

Now the application crashes, when I try to open a QMessageBox with either show() or exec() or whatever.

I am quite sure, that this is not my fault and that it is exactly this combination.

I wrote a quite minimal example project, that shows the problem.

This is the delegate's paint() (the code has been taken from the documentation of QAbstractItemDelegate):

void ItemDelegate::paint(QPainter *painter, const QStyleOptionViewItem &option, const QModelIndex &index) const
{
    QStyleOptionProgressBar progressBarOption;
    progressBarOption.rect = option.rect;
    progressBarOption.minimum = 0;
    progressBarOption.maximum = 100;
    progressBarOption.progress = index.data().toInt();
 
    // This line crashes a QMessageBox. CE_ProgressBarContents and CE_ProgressBar lead to a crash. 
    // All other values of QStyle::CE_*** work fine.
    // drawComplexControl has no problem either.
    QApplication::style()->drawControl(QStyle::CE_ProgressBarContents, &progressBarOption, painter);
}

void ItemDelegate::paint(QPainter *painter, const QStyleOptionViewItem &option, const QModelIndex &index) const
{
    QStyleOptionProgressBar progressBarOption;
    progressBarOption.rect = option.rect;
    progressBarOption.minimum = 0;
    progressBarOption.maximum = 100;
    progressBarOption.progress = index.data().toInt();

    // This line crashes a QMessageBox. CE_ProgressBarContents and CE_ProgressBar lead to a crash. 
    // All other values of QStyle::CE_*** work fine.
    // drawComplexControl has no problem either.
    QApplication::style()->drawControl(QStyle::CE_ProgressBarContents, &progressBarOption, painter);
}

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This is the main window constructor

m_model = new QStandardItemModel(this);
 
    for(int i = 0; i < 10; ++i) {
        QStandardItem *item = new QStandardItem(QString::number(i * 10));
        m_model->appendRow(item);
    }
 
    ui->treeView->setModel(m_model);
    ui->treeView->setItemDelegate(new ItemDelegate(this));

m_model = new QStandardItemModel(this);

    for(int i = 0; i < 10; ++i) {
        QStandardItem *item = new QStandardItem(QString::number(i * 10));
        m_model->appendRow(item);
    }

    ui->treeView->setModel(m_model);
    ui->treeView->setItemDelegate(new ItemDelegate(this));

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And this main() crashes:

MainWindow w;
    w.show();
 
    QMessageBox msgBox;
    msgBox.show();
 
    return a.exec();

MainWindow w;
    w.show();

    QMessageBox msgBox;
    msgBox.show();
    
    return a.exec();

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This is the stacktrace:

0	QCoreApplication::notifyInternal			0x100bd50f0	
1	QStyleAnimation::updateTarget			0x10009312f	
2	QMacStyle::drawControl			0x100021169	
3	QCommonStyle::drawControl			0x1000a0065	
4	QMacStyle::drawControl			0x1000257f1	
5	QPushButton::paintEvent			0x100194eea	
6	QWidget::event			0x10006fece	
7	QAbstractButton::event			0x1001073fd	
8	QPushButton::event			0x100195841	
9	QApplicationPrivate::notify_helper			0x1000397a7	
10	QApplication::notify			0x10003ac0a	
11	QCoreApplication::notifyInternal			0x100bd510e	
12	QWidgetPrivate::drawWidget			0x10006ae8f	
13	QWidgetPrivate::paintSiblingsRecursive			0x10006b6c4	
14	QWidgetPrivate::drawWidget			0x10006b20f	
15	QWidgetPrivate::paintSiblingsRecursive			0x10006b6c4	
16	QWidgetPrivate::drawWidget			0x10006b20f	
17	QWidgetBackingStore::sync			0x1000449d6	
18	QWidgetPrivate::syncBackingStore			0x100062cf7	
19	QWidget::event			0x1000704bb	
20	QMessageBox::event			0x10021849b	
...	<Mehr>

0	QCoreApplication::notifyInternal			0x100bd50f0	
1	QStyleAnimation::updateTarget			0x10009312f	
2	QMacStyle::drawControl			0x100021169	
3	QCommonStyle::drawControl			0x1000a0065	
4	QMacStyle::drawControl			0x1000257f1	
5	QPushButton::paintEvent			0x100194eea	
6	QWidget::event			0x10006fece	
7	QAbstractButton::event			0x1001073fd	
8	QPushButton::event			0x100195841	
9	QApplicationPrivate::notify_helper			0x1000397a7	
10	QApplication::notify			0x10003ac0a	
11	QCoreApplication::notifyInternal			0x100bd510e	
12	QWidgetPrivate::drawWidget			0x10006ae8f	
13	QWidgetPrivate::paintSiblingsRecursive			0x10006b6c4	
14	QWidgetPrivate::drawWidget			0x10006b20f	
15	QWidgetPrivate::paintSiblingsRecursive			0x10006b6c4	
16	QWidgetPrivate::drawWidget			0x10006b20f	
17	QWidgetBackingStore::sync			0x1000449d6	
18	QWidgetPrivate::syncBackingStore			0x100062cf7	
19	QWidget::event			0x1000704bb	
20	QMessageBox::event			0x10021849b	
...	<Mehr>

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The example project can be found on my GitHub: https://github.com/Kampfgnom/QMessageBoxCrash

I am using Qt 5.0.1 on Mac OS X 10.8.2. Is this a Qt bug? How would you work around it?

[Kampfgnom]

Since I didn't get any replies in here or on stackoverflow, I filed a bug report: QTBUG-29748

[alrawab]

sorry wrong post

[norobro]

Your app works fine on Debian & Qt 5.0.1.

[Kampfgnom]

Thanks for the confirmation :-)

Since at one point in the stack trace QMacStyle::drawControl is called, I assumed that this issue is Mac only. I am quite the Sherlock :-)

[Kampfgnom]

This was in fact a Qt bug. It will be fixed in 5.0.2.