Disable specific items in QComboBox - qt

Question

In my application, I want to disable some items (i.e. not selectable, no highlights when mouse hovering above, and the texts are greyed out) in the QComboBox when certain conditions are met.
I indeed found someone did ask the same question here: Disable Item in Qt Combobox
But none of these solutions in the answers seem to actually work (including the trick).
Is there a decent and 'correct' way to implement this?
EDIT:
I found out why setting the flags wouldn't disable the items in my application: for some reasons, I had to set the style QStyle::SH_ComboBox_UseNativePopup(see https://codereview.qt-project.org/#/c/82718/). And this setting for some reasons blocked the flag setting. Does anyone have an idea why, and how to work around? A minimum test example is included (modified from the answer of #Mike):
#include <QApplication>
#include <QComboBox>
#include <QStandardItemModel>
#include <QProxyStyle>
class ComboBoxStyle : public QProxyStyle
{
public:
int styleHint ( StyleHint hint, const QStyleOption * option = 0, const QWidget * widget = 0, QStyleHintReturn * returnData = 0 ) const override
{
if ( hint == QStyle::SH_ComboBox_UseNativePopup )
{
return 1;
}
return QProxyStyle::styleHint( hint, option, widget, returnData );
}
};
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
QComboBox comboBox;
// Setting this style would block the flag settings later on.
comboBox.setStyle( new ComboBoxStyle() );
comboBox.insertItem(0, QObject::tr("item1"));
comboBox.insertItem(1, QObject::tr("item2"));
QStandardItemModel* model = qobject_cast<QStandardItemModel*>(comboBox.model());
QStandardItem* item= model->item(1);
item->setFlags(item->flags() & ~Qt::ItemIsEnabled);
comboBox.show();
return a.exec();
}

Answer 1

The answer linked in my comment above seems to be talking about an old version of Qt. I have tested on Qt5.4 and Qt5.6 and there is no need set the color yourself here, you just need to set and/or clear the Qt::ItemIsEnabled flag, here is an example:
#include <QtWidgets>
int main(int argc, char *argv[]) {
QApplication a(argc, argv);
QComboBox comboBox;
comboBox.addItem(QObject::tr("item1"));
comboBox.addItem(QObject::tr("item2"));
comboBox.addItem(QObject::tr("item3"));
QStandardItemModel *model =
qobject_cast<QStandardItemModel *>(comboBox.model());
Q_ASSERT(model != nullptr);
bool disabled = true;
QStandardItem *item = model->item(2);
item->setFlags(disabled ? item->flags() & ~Qt::ItemIsEnabled
: item->flags() | Qt::ItemIsEnabled);
comboBox.show();
return a.exec();
}

Answer 2

Here is the technique #Mike describes, wrapped up in a convenient utility function:
void SetComboBoxItemEnabled(QComboBox * comboBox, int index, bool enabled)
{
auto * model = qobject_cast<QStandardItemModel*>(comboBox->model());
assert(model);
if(!model) return;
auto * item = model->item(index);
assert(item);
if(!item) return;
item->setEnabled(enabled);
}