what is QComboBox::rootModelIndex?

[scarleton]

What is QComboBox::rootModelIndex? I searched the web and cannot find anything, I even searched through the Qt source and only found one reference to it in the qfiledialog.cpp, but it makes little sense. Can anyone enlighten me?

[Lykurg]

You need it when working with a tree model. Compare:
#include <QtGui>

int main(int argc, char *argv[])
{

QApplication app(argc, argv);

QStandardItemModel model;
QStandardItem *parentItem = model.invisibleRootItem();
for (int i = 0; i < 5; ++i)
{
QStandardItem *item = new QStandardItem(QString("Root %1").arg(i));
for (int j = 0; j < 5; ++j)
{
QStandardItem *itemSub = new QStandardItem(QString("%1:%2").arg(i).arg(j));
item->appendRow(itemSub);
}
parentItem->appendRow(item);
}

QComboBox b;
b.setModel(&model);
b.show();

QComboBox b2;
b2.setModel(&model);
b2.setRootModelIndex(model.index(1,0));
b2.show();

return app.exec();
}