ListView with QSortFilterProxyModel displays empty lines resulting to the error "Unable to assign [undefined] to QString"

mbruel

Hi,

My app is using a ListView with its model coming from C++. Everything was ok using my custom QAbstractListModel following the doc.

I now wish to add a filtering feature and thus, I've switched the model to be a QSortFilterProxyModel whose source is my QAbstractListModel.
It is working but I've an issue I'd like to remove.

Basically if my model doesn't fill the whole ListView, let's say only 7 rows where the view could display 10, then with a QSortFilterProxyModel, blank rows are displayed and selectable so I'm getting this error in the console: qrc:/Playlist.qml:54:17: Unable to assign [undefined] to QString
Any idea what I should do to remove this behaviour?

This is not happening when I'm using a QAbstractListModel. It's quite a bad user experience to be able to select blank rows. cf this snapshot
alt text

I've tried to do a Custom QSortFilterProxyModel as I'll need it anyway and try to trick the filter function to only accept valid rows but it doesn't seem to work. Here would be the code:

bool PlayListProxyModel::filterAcceptsRow(int sourceRow, const QModelIndex &sourceParent) const
{
    ClementineRemote *remote = static_cast<PlayListModel *>(sourceModel())->remote();
    if (sourceRow < remote->nbSongs())
        return true;
    else
        return false;
}

I suppose sourceRow is the index on the model. remote->nbSongs() is returning the number of elements the model is exposing.

Any idea what I could do?

Edit1: if I display the ListView.count, I'm getting 14 using the QSortFilterProxyModel, 7 as expected with a QAbstractListModel. if it is the double exactly there must be a reason no?

Edit2: no in fact it is random, if I use 8 elements in the model, I'm getting 11 rows in the view using the proxy (8 with the model)

mbruel

wow really weird I found a way to make the BUG disappear by adding a debug which display the rowCount on the proxy model before I'm modifying the data (signalling the Model....)
I didn't understand yesterday how I managed to fix the issue.
Today by removing my debugs, the bug came back. By checking my commits, I managed to find up one debug line was needed to remove the bug...
Here is my code to populate my data and Model:

void ClementineRemote::rcvPlaylistSongs(pb::remote::ResponsePlaylistSongs *songs)
{
    // HACK to resolve ListView issue (displaying empty Rows after the number of elements)
    // cf https://forum.qt.io/topic/120302/listview-with-qsortfilterproxymodel-displays-empty-lines-resulting-to-the-error-unable-to-assign-undefined-to-qstring
    qint32 proxyRows = _playlistProxyModel->rowCount();
//    qDebug() << "proxy row count before removal: " << proxyRows;

    emit preClearSongs(_songs.size() - 1);
    _songs.clear();
    emit postSongRemoved();

    emit preAddSongs(songs->songs_size() -1 );
    _songs.reserve(songs->songs_size());
    for (auto it = songs->songs().cbegin(), itEnd = songs->songs().cend();  it != itEnd; ++it)
        _songs.append(*it);
    emit postSongAppended();
}

So basically my model is connected on the _song list with those connections:

void PlayListModel::setRemote(ClementineRemote *remote)
{
    beginResetModel();

    if (_remote)
        _remote->disconnect(this);

    _remote = remote;

    if (_remote) {
        connect(_remote, &ClementineRemote::preAddSongs, this, [=](int lastSongIdx) {
            beginInsertRows(QModelIndex(), 0, lastSongIdx);
        });
        connect(_remote, &ClementineRemote::postSongAppended, this, [=]() {
            endInsertRows();
        });

        connect(_remote, &ClementineRemote::preClearSongs, this, [=](int lastSongIdx) {
            beginRemoveRows(QModelIndex(), 0, lastSongIdx);
        });
        connect(_remote, &ClementineRemote::postSongRemoved, this, [=]() {
            endRemoveRows();
        });
    }

    endResetModel();
}

So any idea what I'm doing wrong or why do I need to call this qint32 proxyRows = _playlistProxyModel->rowCount(); in order for the ListView to get the correct number of rows on the proxy once the Model is repopulated?
Is it a bug?

mbruel

The issue comes from the fact I'm updating the data from a ConnectionWorker Thread instead of the GUI one...
I've opened another thread more general to see how I could fix that.