Qt subclassed QStyledItemDelegate paint method is never called

Update: my paint method was not const

I have a custom QTableView connected to a QAbstractTableModel.

I recently created a QStyledItemDelegate subclass and its paint method prints a debugging message and then it calls the parent paint and then it prints another debugging message.

I have called view->setItemDelegate and I have checked that the item delegate in my view is the one I gave it (just to be sure).

However, my program just renders things the same way it did before and never prints the debug message in paint. It does print a debug message in the delegate's constructor, so I know it should be printing if that function ever gets called.

Here is a stripped down version of my code, let me know one of these:

1. Can you see what is wrong?
2. How I can debug Qt classes like this?
3. What other relevant code I should post to diagnose this proble开发者_如何学Pythonm?
4. Is there some common solution I could try?

Thanks!

Here is the entire delegate .h and .cpp files (minus includes/namespace)

class QtCellItemDelegate : public QStyledItemDelegate
{
    Q_OBJECT;
public:
    QtCellItemDelegate( QWidget *parent = NULL );

    void paint( QPainter *painter,
                const QStyleOptionViewItem &option,
                const QModelIndex &index );

    QSize sizeHint( const QStyleOptionViewItem &option,
                    const QModelIndex & index ) const;

    virtual ~QtCellItemDelegate();
};

QtCellItemDelegate::QtCellItemDelegate( QWidget *parent ) :
    QStyledItemDelegate( parent )
{
    qDebug() << "CONSTRUCT";
}

void QtCellItemDelegate::paint( QPainter *painter,
                                const QStyleOptionViewItem &option,
                                const QModelIndex &index )
{
    painter->save();
    qDebug() << "Begin Paint";
    QStyledItemDelegate::paint( painter, option, index );

    qDebug() << "   Begin custom paint";
    // omitted...

    qDebug() << "End paint";
    painter->restore();
}

QSize QtCellItemDelegate::sizeHint( const QStyleOptionViewItem &option,
                                     const QModelIndex & index ) const 
{
    return QSize( 60, 60 );
}

QtCellItemDelegate::~QtCellItemDelegate()
{
    qDebug() << "Destroy delegate!";
}

So the debugging output tells me the constructor is called (but not the destructor...) and that I am actaully setting the same deleagate to the view as I think I am. However, the messages in paint never get printed.

I think your problem is that you are not declaring your subclass's paint method as const. As such, it's not overriding the superclass method (const and non-const methods are considered to have different signatures from each other) and that's why your paint method doesn't get called.