lambda slots and QNetworkReply

[Mark81]

I'm doing something wrong in this code:

void Packages::download(Package_t package)
{
    _currentFilename = package.filename;
    _currentFile.setFileName(QString("/mnt/resources/packages/%1").arg(_currentFilename));
    if (!_currentFile.open(QIODevice::WriteOnly))
    {
        qWarning() << "Cannot open" << _currentFile.fileName();
        return;
    }

    QUrlQuery query;
    query.addQueryItem("filename", package.filename);

    QUrl url(API_HOST + API_DOWNLOAD);
    url.setQuery(query);

    QNetworkRequest request(url);
    _managerDownload.setTransferTimeout(10000);
    QNetworkReply *reply = _managerDownload.get(request);

    connect(reply, &QNetworkReply::downloadProgress, [reply, this](qint64 bytesReceived, qint64 bytesTotal)
    {
        _currentFile.write(reply->readAll());
        qInfo() << "progress" << bytesReceived << "/" << bytesTotal;
    });

    connect(&_managerDownload, &QNetworkAccessManager::finished, [this](QNetworkReply *reply)
    {
        reply->deleteLater();
        int status = reply->attribute(QNetworkRequest::HttpStatusCodeAttribute).toInt();
        qInfo() << "HTTP status:" << status << reply->url();
        switch (status)
        {
        case 200: qInfo() << "Download completed successfully"; break;
        case 404: qInfo() << "File not found"; break;
        default: break;
        }

        _currentFile.close();
        emit downloadFinished(status, _currentFilename);
    });

    qInfo() << "GET request" << request.url();
}

Basically it should:

1. open a local file where to store the downloaded binary data
2. create the HTTP GET request
3. bind the downloadProgress and finished signals to the two lambda functions

It works, but every time I call this function I see more and more messages, like it does not destroy the previous objects.
I don't get the mistake because:

• _managerDownload is a class member, not a pointer
• reply is deleted inside the finished slot

Can you help me to understand my fault please?

[Christian Ehrlicher]

@Mark81 said in lambda slots and QNetworkReply:

connect(reply, &QNetworkReply::downloadProgress, [reply, this](qint64 bytesReceived, qint64 bytesTotal)
{
    _currentFile.write(reply->readAll());
    qInfo() << "progress" << bytesReceived << "/" << bytesTotal;
});

You should do this once since there's no disconnect because you forgot to specify the receiver's object (third parameter): https://doc.qt.io/qt-5/qobject.html#connect-4 and https://doc.qt.io/qt-5/qobject.html#connect-5 --> set reply as context to make sure the slot gets disconnected or connect only once (which I would prefer)

[J.Hilk]

@Mark81 said in lambda slots and QNetworkReply:

change this

connect(&_managerDownload, &QNetworkAccessManager::finished, [this](QNetworkReply *reply)

to

connect(&_managerDownload, &QNetworkAccessManager::finished, reply, [this](QNetworkReply *reply)

the reply object in 3rd place should guarantee, that this connect is dissolved once reply is deleted