SizeHint() always returns default values

Asperamanca · wrote on 14 Mar 2012, 15:35

I have a QGraphicsWidget subclass, which is managed in a QGraphicsGridLayout.

The subclass calls setMinimumSize(68, 34) and setSizePolicy (Horizontal: MinimumExpanding, Vertical: Minimum).

My problem is that the layout did not honor this minimum size. A couple of hours debugging and tracing later, I realized that every call to QGraphicsWidget::sizeHint(Qt::MinimumSize) always returns QSizeF(0,0) instead of the size I had set previously.

I traced by subclassing sizeHint this way:

@QSizeF CGlib_GraphicsTimeScaleWidget::sizeHint(Qt::SizeHint which, const QSizeF &constraint) const
{
QSizeF size = QGraphicsWidget::sizeHint(which, constraint);

qDebug() << "TimeScaleWidget::sizeHint" <<
            "which:" << which <<
            "constraint:" << constraint <<
            "resulting sizeHint:" << size;
return size;

}@

The results:
@TimeScaleWidget::sizeHint which: 2 constraint: QSizeF(-1, -1) resulting sizeHint: QSizeF(1.67772e+07, 1.67772e+07)
TimeScaleWidget::sizeHint which: 0 constraint: QSizeF(-1, -1) resulting sizeHint: QSizeF(0, 0)
TimeScaleWidget::sizeHint which: 1 constraint: QSizeF(-1, -1) resulting sizeHint: QSizeF(50, 50)
Updating minimum size to QSizeF(68, 34) size policy to horiz: 3 vert: 1
TimeScaleWidget::sizeHint which: 2 constraint: QSizeF(-1, -1) resulting sizeHint: QSizeF(1.67772e+07, 1.67772e+07)
TimeScaleWidget::sizeHint which: 1 constraint: QSizeF(-1, -1) resulting sizeHint: QSizeF(50, 50)
TimeScaleWidget::sizeHint which: 0 constraint: QSizeF(-1, -1) resulting sizeHint: QSizeF(0, 0) @

After the "Updating minimum size" call, I would expect the minimum size to return QSizeF(68, 34).

When debugging into qgraphicswidget.cpp, I see that for my object, d->layout is Null. How can that be? The object is inside a grid layout, and I can see it's position is managed by the layout (I don't otherwise set the object's size and position). But because d->layout is Null, I only get the default values for size hints, instead of the minimum size I set myself.

For the sake of completeness, here is the content of my layout:

@
m_pMainLayout->addItem(m_pAnalogLegend,0,0,2,1);
m_pMainLayout->addItem(m_pDateLabel,2,0);
m_pMainLayout->addItem(m_pBinaryLegend,3,0,1,2);
m_pMainLayout->addItem(m_pValueScale,0,1);
m_pMainLayout->addItem(m_pAnalogCurveCanvas,0,2);
// This is the item I am tracing
m_pMainLayout->addItem(m_pTimeScale,1,2,2,1);
//
m_pMainLayout->addItem(m_pBinaryCurveCanvas,3,2,1,1);
m_pMainLayout->addItem(m_pButtonBar,4,0,1,3);@

Any ideas what might go wrong here?

Asperamanca · wrote on 15 Mar 2012, 10:32

Posted as bug:

https://bugreports.qt-project.org/browse/QTBUG-24805