[Solved] Cannot draw checkbox in QStyledItemDelegate

cmannett85

I have a QStyledItemDelegate derived object for a QTableView derived view. I further delegate the painting and editor creation depending on the model index data type. For bools I wanted to represent the state via a checkbox - but the check box never appears.

Here is the base delegate paint function:

@void Sy_QtPropertyDelegate::paint( QPainter* painter,
const QStyleOptionViewItem& option,
const QModelIndex& index ) const
{
painter->save();

if ( index.column() == 0 ) {
    ...
} else {
    QVariant var = index.data();
    bool modified = index.data( Sy_QtPropertyModel::ModifiedRole ).toBool();

    //  If the data type is one of our delegates, then push the work onto
    //  that.
    auto it = delegateMap_.find( var.type() );
    if ( it != delegateMap_.end() ) {
        ( *it )->paint( painter, option, index );
    } else if ( var.type() != QVariant::UserType ) {
        ...
    } else {
        ...
    }
}

painter->restore();

}@

And the bool sub delegate paint function:

@void Sy_boolPD::paint( QPainter* painter,
const QStyleOptionViewItem& option,
const QModelIndex& index ) const
{
painter->save();

bool checked  = index.data().toBool();
bool modified = index.data( Sy_QtPropertyModel::ModifiedRole ).toBool();

QStyle* style = Sy_application::style();
if ( modified ) {
    QStyleOptionViewItemV4 bgOpt( option );
    bgOpt.backgroundBrush = QBrush( Sy_QtPropertyDelegate::ModifiedColour );
    style->drawControl( QStyle::CE_ItemViewItem, &bgOpt, painter );
}

QStyleOption butOpt( option );
butOpt.state = QStyle::State_Enabled;
butOpt.state |= checked ? QStyle::State_On : QStyle::State_Off;
style->drawControl( QStyle::CE_CheckBox, &butOpt, painter );

painter->restore();

}@

If I force modified to be true, the background is colour of the table is appropriately changed, and cout-ing butOpt's rect and state members show that they are correct - but no check box is shown!

I've worked with Qt's MVC framework a lot, but I cannot see where I have gone wrong here.

cmannett85

Setting

@style->drawControl( QStyle::CE_CheckBox, &butOpt, painter );@

To draw any other ControlElement type still causes nothing to render, so it's not a problem specific to check boxes.

cmannett85

All I had to do was look in the source code...

@case CE_CheckBox:
if (const QStyleOptionButton *btn = qstyleoption_cast<const QStyleOptionButton *>(option)) {
...
}@

The QStyleOption I pass to the method is cast to the type specific for drawing the control, CE_CheckBox requires a QStyleOptionButton, and if the cast fails the drawing operation silently skips.

qxoz

Thank you for sharing your experience.