Get checkbox of QStandardItem

[Neptilo]

I have a custom QComboBox using a model in which I set some QStandardItems. I made these items checkable:

item->setFlags(Qt::ItemIsUserCheckable | Qt::ItemIsEnabled);

item->setFlags(Qt::ItemIsUserCheckable | Qt::ItemIsEnabled);

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The problem is when I deploy my app for Android, the checkboxes are so small I cannot even click on them. That's why I would like to set a style for them, so my question is: how do I get the checkbox objects of a QStandardItem so I can call QWidget::setStyle() on them?

Additional issue to be taken into account: the checkboxes do not always show up depending on the OS, so I'm using one of these workarounds:

• set another style for my QComboBox, which will display the checkboxes correctly
• set a custom QStyledItemDelegate with a redefined QStyledItemDelegate::paint() method, as suggested in a Stackoverflow thread

[wysota]

There are no checkbox objects. The boxes are drawn by a delegate, so the easiest approach is to provide a custom delegate that will draw the boxes the way you want.

[Neptilo]

Thanks for your answer.

Ok then how do I find which image file Qt was using before, so I can paint it again in a bigger size? Looking into the source of QStyledItemDelegate did not provide any information about that.

How can I paint an image in a delegate? The QStyledItemDelegate doc does not seem to cover painting images.

And most importantly, how do I tell Qt that the painted image is the actual checkbox (so when I click it the item changes the value of its Qt::CheckStateRole)?

[wysota]

Have a look at QStylePainter. Regarding the second question, the delegate handles events for items in editorEvent() method, you have to implement a hit test there and update the model if you hit the checkbox.

[Neptilo]

Thanks. I'm playing around with QStylePainter right now. I'll let you know if I get to achieve what I want.

[wysota]

What you want is probably drawControl() and QStyle::CE_CheckBox.

[Neptilo]

So how to use these?

I'm not sure but I suspect this will paint the default icons in their default size, so much too small in the case of Android. Or are you thinking of a way to resize them?

Anyway I'm experimenting with the advice in your previous post now and I feel like it will do fine.

[Neptilo]

I managed to get by with the paint() method, but I'm kinda stuck with editorEvent(). Edit: I had a look at QItemDelegate source and found how to do it:

bool CheckableItemDelegate::editorEvent(QEvent *event, QAbstractItemModel *model, const QStyleOptionViewItem &option, const QModelIndex &index)
{
    Q_UNUSED(option);
    if (event->type() == QEvent::MouseButtonRelease) {
        QVariant value = index.data(Qt::CheckStateRole);
        Qt::CheckState state = (static_cast<Qt::CheckState>(value.toInt()) == Qt::Checked
                                ? Qt::Unchecked : Qt::Checked);
        return model->setData(index, state, Qt::CheckStateRole);
    } else
        return false;
}

bool CheckableItemDelegate::editorEvent(QEvent *event, QAbstractItemModel *model, const QStyleOptionViewItem &option, const QModelIndex &index)
{
    Q_UNUSED(option);
    if (event->type() == QEvent::MouseButtonRelease) {
        QVariant value = index.data(Qt::CheckStateRole);
        Qt::CheckState state = (static_cast<Qt::CheckState>(value.toInt()) == Qt::Checked
                                ? Qt::Unchecked : Qt::Checked);
        return model->setData(index, state, Qt::CheckStateRole);
    } else
        return false;
}

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This will intercept all mouse clicks on the item (and I'm ok with it).

[Neptilo]

Update:

I think I nailed it, hinted by this post.

So I subclassed QProxyStyle as AndroidStyle and reimplemented QProxyStyle::pixelMetric this way:

int AndroidStyle::pixelMetric(PixelMetric which,
                             const QStyleOption *option,
                             const QWidget *widget) const
{
    int metric = QProxyStyle::pixelMetric(which, option, widget);
    switch (which) {
    case PM_IndicatorWidth:
    case PM_IndicatorHeight:
        return 2*metric;
    default:
        return metric;
    }
}

int AndroidStyle::pixelMetric(PixelMetric which,
                             const QStyleOption *option,
                             const QWidget *widget) const
{
    int metric = QProxyStyle::pixelMetric(which, option, widget);
    switch (which) {
    case PM_IndicatorWidth:
    case PM_IndicatorHeight:
        return 2*metric;
    default:
        return metric;
    }
}

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and I set this style in the main function like this:

QApplication a(argc, argv);
a.setStyle(new AndroidStyle);

QApplication a(argc, argv);
a.setStyle(new AndroidStyle);

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