QModelIndex value for the root of a tree model

[anda_skoa]

To get the index value of a top level item, I need to send the row and column of the item and the index value of the item's parent (which technically is the root) to the index function. That obviously results in an invalid index value being returned.

Not obvious at all, this should return a valid index if the model has such a cell:

if (model->rowCount(QModelIndex()) > 0 && model->columnCount(QModelIndex()) > 0) {
    QModelIndex topLevelRow0Column0 = model->index(0, 0, QModelIndex());
    Q_ASSERT(topLevelRow0Column0.isValid());
}

if (model->rowCount(QModelIndex()) > 0 && model->columnCount(QModelIndex()) > 0) {
    QModelIndex topLevelRow0Column0 = model->index(0, 0, QModelIndex());
    Q_ASSERT(topLevelRow0Column0.isValid());
}

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If the index is not valid despite this cell being part of the model, then there must a problem with the model's index() implementation.

The index() and the parent() method are the two tricky ones when implementing a tree model, so things can go wrong there.

See https://wiki.qt.io/Model_Test for a simple standard test harness for models and also check out https://www.kdab.com/development-res...ools/gammaray/ (has a model inspector plugin)

Cheers,
_