A bug of QLayout

[cocalele]

Hi,
I just find a assert failure when I use QLayout. I want know is this a bug of QLayout.
The QLayout has a constructor like this, which need a parent of QWdiget

QLayout::QLayoutQWidget *parent)
    : QObject(*new QLayoutPrivate, parent)
{
    if (!parent)
        return;
    parent->setLayout(this);
}

QLayout::QLayoutQWidget *parent)
    : QObject(*new QLayoutPrivate, parent)
{
    if (!parent)
        return;
    parent->setLayout(this);
}

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But in the code of QLayout:arentWidget() (line 6), it trys to cast the parent to QLayout

QWidget *QLayout::parentWidget() const
{
    Q_D(const QLayout);
    if (!d->topLevel) {
        if (parent()) {
            QLayout *parentLayout = ::qobject_cast<QLayout*>(parent()); 
           Q_ASSERT(parentLayout);
            return parentLayout->parentWidget();
        } else {
            return 0;
        }
    } else {
        Q_ASSERT(parent() && parent()->isWidgetType());
        return static_cast<QWidget *>(parent());
    }
}

QWidget *QLayout::parentWidget() const
{
    Q_D(const QLayout);
    if (!d->topLevel) {
        if (parent()) {
            QLayout *parentLayout = ::qobject_cast<QLayout*>(parent()); 
           Q_ASSERT(parentLayout);
            return parentLayout->parentWidget();
        } else {
            return 0;
        }
    } else {
        Q_ASSERT(parent() && parent()->isWidgetType());
        return static_cast<QWidget *>(parent());
    }
}

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certainly, cast from QWidget* to QLayout* will failled, and the successed assertion will failed. Is this a bug or anything I don't know?
Thanks for your help!

[dimitri]

Could you provide a minimal example that reproduces the problem? I don't think there's a bug (the parent constructor argument and parent() are different) but it's hard to tell without some code to reproduce the failed assertion.

[cocalele]

here's some code reproduce the error

HelloQt::HelloQt(QWidget *parent, Qt::WFlags flags)
    : QDialog(parent, flags)
{
	QHBoxLayout *topMostLayout = new QHBoxLayout(this);
 
	//QVBoxLayout *subLayout = new QVBoxLayout(this); //addLayout will fail
	QVBoxLayout *subLayout = new QVBoxLayout(); //It's OK
 
	topMostLayout->addLayout(subLayout);
 
}

HelloQt::HelloQt(QWidget *parent, Qt::WFlags flags)
    : QDialog(parent, flags)
{
	QHBoxLayout *topMostLayout = new QHBoxLayout(this);

	//QVBoxLayout *subLayout = new QVBoxLayout(this); //addLayout will fail
	QVBoxLayout *subLayout = new QVBoxLayout(); //It's OK

	topMostLayout->addLayout(subLayout);

}

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[dimitri]

I mean a minimal complete program that I could build to reproduce what you're seeing.

[jpn]

QHBoxLayout *topMostLayout = new QHBoxLayout(this);
QVBoxLayout *subLayout = new QVBoxLayout(this); //addLayout will fail

QHBoxLayout *topMostLayout = new QHBoxLayout(this);
QVBoxLayout *subLayout = new QVBoxLayout(this); //addLayout will fail

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This is non-sense. Passing a parent widget to layout constructor is same than setting the layout as widget's layout. So what the code above does is it tries to set 2 different layouts one after another to a same widget.

Attempting to add QLayout "" to QDialog "", which already has a layout.

Anyhow, all it does for me is showing the warning. No assertion fails for me with Qt 4.1.2..
Which version are you using?

Edit: Check this task tracker entry.

[cocalele]

I mean a minimal complete program that I could build to reproduce what you're seeing.

Thanks for your help! I have attached my whole test code in HelloQt.zip.

The assert fail is not in the constructor of subLayout, but in the code add sublayout to the topmost layout.

I use Qt4.1.0

[jpn]

Did you check the task tracker entry link I provided? This has already been fixed in Qt 4.1.1.
Changes 4.1.1: "QLayout: Warn instead of crash when adding two layouts to a widget."

So consider updating to the newest Qt.