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();
}

#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();
}

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