Crash sorting QTreeView using QSortFilterProxyModel

Sriep

Hi

I have a QTreeView widget that I am has sorting implemented by clicking the headers. The sorting works ok, but the program after fiddling the program eventually crashes with

FATAL: qabstractitemmodel.cpp:643 - ASSERT failure in QPersistentModelIndex::~QPersistentModelIndex: "persistent model indexes corrupted", file itemmodels\qabstractitemmodel.cpp, line 643

A derived class
class CredentialModelFilter : public QSortFilterProxyModel
is used for the sorting. The less than function is

/
bool CredentialModelFilter::lessThan(const QModelIndex &srcLeft, const QModelIndex &srcRight) const
{
    // Get src model
    CredentialModel *pSrcModel = dynamic_cast<CredentialModel *>(sourceModel());

    TreeItem *pLeftItem = pSrcModel->getItemByIndex(srcLeft);
    TreeItem *pRightItem = pSrcModel->getItemByIndex(srcRight);

    if ((pLeftItem != nullptr) && (pRightItem != nullptr))
        return pLeftItem->name() < pRightItem->name();

    return false;
}

Taking note of http://doc.qt.io/qt-5/model-view-programming.html I tried overriding the sort function like

void CredentialModelFilter::sort(int column, Qt::SortOrder order)
{
    emit layoutAboutToBeChanged();
    QModelIndexList oldPersistantIndexes = persistentIndexList();

    QSortFilterProxyModel::sort(column, order);

    QModelIndexList newPersistantIndexes = persistentIndexList();
    changePersistentIndexList(oldPersistantIndexes, newPersistantIndexes);
    emit layoutChanged();
}

Unfortunately, that did not make any difference, it still crashes on a subsequent click in the QTreeView.. I tried various other permutations to no effect.

So any suggestions as to sort without messing everything up?

VRonin

Unfortunately it looks like it's not a problem of sorting or of the proxy. CredentialModel is probably not implemented correctly. Subclassing QAbstractItemModel is a minefield and if you don't do it correctly a lot of stuff will stop working. In your case, the persistent model indexes do not update correctly when the model changes and they become corrupt.

A good place to start is the model test. download modeltest.h and modeltest.cpp. When you create the source model (you have something like CredentialModel* myModel = new CredentialModel(this);) add a line with new ModelTest(myModel ,this); and use it as normal. it will assert if it detects something wrong

P.S.
My suggestion is always to use QStandardItemModel and switch to a custom model only if you have serious performance needs

Sriep

@VRonin Thanks for your help.

I looked at Model_Test. Some thoughts.
The usage instructions were not very good. The .pri file mentioned was probably removed years ago.
I followed the instructions about including modeltest.h in the code but with no result.
The group of 6 files make an interesting test project. With dynamictreemodel.h/cpp being a custom QAbstractItemModel object to be tested. and tst_modeltest.cpp being a test script that you need to modify to fit your own model. So it needs a bit of work to get working, and the model I was working on passed all the tests.

Sriep

The issue I have occurs in this bit of code bellow from QAbstractItemModelPrivate::removePersistentIndexData. The Q_ASSERT_X happens. This is during a mouse press and setCurrentIndex in the QTreeView.

I put in some debug code that calls QAbstractItemModel::persistentIndexList and dumps the list to debug. I put this in the virtual CredentialModel::parent function. The only time any persistent indexes appear is during a sort, and they are removed by the time the sort function is exited.

QItemSelectionModel::setCurrentIndex is called when clicking on the QTreeView GUI object. This function creates a QPeristentModelIndex called previous. The assert seems to happen when this object is deleted on leaving scope.

void QItemSelectionModel::setCurrentIndex(const QModelIndex &index, QItemSelectionModel::SelectionFlags command)
{
...
    QPersistentModelIndex previous = d->currentIndex;
    d->currentIndex = index; // set current before emitting selection changed below
    if (command != NoUpdate)
        select(d->currentIndex, command); // select item
    emit currentChanged(d->currentIndex, previous);
    if (d->currentIndex.row() != previous.row() ||
            d->currentIndex.parent() != previous.parent())
        emit currentRowChanged(d->currentIndex, previous);
    if (d->currentIndex.column() != previous.column() ||
            d->currentIndex.parent() != previous.parent())
        emit currentColumnChanged(d->currentIndex, previous);
}

This is the point of the assert

void QAbstractItemModelPrivate::removePersistentIndexData(QPersistentModelIndexData *data)
{
    if (data->index.isValid()) {
        int removed = persistent.indexes.remove(data->index);
        Q_ASSERT_X(removed == 1, "QPersistentModelIndex::~QPersistentModelIndex",
                   "persistent model indexes corrupted"); //maybe the index was somewhat invalid?
        // This assert may happen if the model use changePersistentIndex in a way that could result on two
        // QPersistentModelIndex pointing to the same index.
        Q_UNUSED(removed);
    }
...
}

VRonin

@Sriep said in Crash sorting QTreeView using QSortFilterProxyModel:

The usage instructions were not very good.

I know, that's why I included the usage instructions above

download modeltest.h and modeltest.cpp [and add them to your project]. When you create the source model (you have something like CredentialModel* myModel = new CredentialModel(this);) add a line with new ModelTest(myModel ,this);