I've subclassed QListWidgetItem like this:

class DutyCodeItem : public QListWidgetItem
{
public:
DutyCodeItem(const VagtkodeDb *kode, QListWidget *parent = 0);
~DutyCodeItem();

virtual bool operator<(const QListWidgetItem &item) const;

virtual QVariant data(int role) const;

const VagtkodeDb* getDutyCode() const;

private:
const VagtkodeDb *m_dutycode;
};

The ctor is implemented like this:

DutyCodeItem::DutyCodeItem(const VagtkodeDb *dutycode, QListWidget *parent)
: QListWidgetItem(parent, 1000)
{
assert(dutycode != NULL);
m_dutycode = dutycode;
}

If I add a new object to a QListWidget like this:

new DutyCodeItem(obj, IDLB_DUTY_CODES);

my subclassed object gets mangled and seems to be reverted to a simple QListWidgetItem. IDLB_DUTY_CODES is a QListWidget, by the way.

This can be verified in the implementation of operator<():

bool DutyCodeItem::operator<(const QListWidgetItem &item) const
{
QListWidgetItem a = const_cast<QListWidgetItem>(&item);

DutyCodeItem rhs = dynamic_cast<DutyCodeItem>(a);
return (m_dutycode < rhs->m_dutycode);
}

If the object was inserted using the ctor then the dynamic cast will return a NULL pointer.

There's a workaround by inserting a new object like this:

DutyCodeItem *item = new DutyCodeItem(obj, 0);
IDLB_DUTY_CODES->addItem(item);

I've found the bug in Qt 4.5.1 and it still seems to be there in subsequent (and probably previous) versions of Qt 4.

However