Cannot draw checkbox in QStyledItemDelegate - c++

Question

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 couting butOpt's rect and state members show that they are correct - but no check box is shown! Setting QStyle::CE_CheckBox to any other type also causes nothing to render.
I've worked with Qt's MVC framework a lot, but I cannot see where I have gone wrong here.

Answer 1

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.