Qt retrieve additional data created during request when QNetworkAccessManager finished - c++

Question

I would like to create an HTTP request and retrieve in the response some variables create during the request.
However, QNetworkAccessManager reponse is asynchronous and use SIGNAL/SLOT functionality, so variable are no more accessible.
Here is an example :
void makeRequest()
{
manager = new QNetworkAccessManager(this);
connect(manager, SIGNAL(finished(QNetworkReply*)),
this, SLOT(replyFinished(QNetworkReply*)));
// here is the datas I want to get in the reply
// objectdata and objectdata2 are created just before the http request
MyClass objectdata("randomseed");
MyClass2 objectdata("randomseed") ;
QUrl websiteurl = objectdata.getUrl();
manager->get(QNetworkRequest(websiteurl));
}
void replyFinished (QNetworkReply *reply)
{
if(reply->error())
{
qDebug() << "ERROR!";
qDebug() << reply->errorString();
}
else
{
QByteArray dataHttp = reply->readAll();
// How can I get here objectdata and objectdata2 ?
// I would like to do something like that this->dataSuccess(objectdata,objectdata2,dataHttp);
}
reply->deleteLater();
}
In a synchronous system this problematic doesn't exist.
Is there a workaround to this problematic ?

Answer 1

One way to do it is to capture the locals in a lambda instead of using a separate function for the slot.
void makeRequest()
{
manager = new QNetworkAccessManager(this);
// here is the datas I want to get in the reply
// objectdata and objectdata2 are created just before the http request
MyClass objectdata("randomseed");
MyClass2 objectdata("randomseed") ;
connect(manager, &QNetworkAccessManager::finished, [this, objectdata, objectdata2](QNetworkReply *reply)
{
if(reply->error())
{
qDebug() << "ERROR!";
qDebug() << reply->errorString();
}
else
{
QByteArray dataHttp = reply->readAll();
dataSuccess(objectdata,objectdata2,dataHttp);
}
reply->deleteLater();
}
QUrl websiteurl = objectdata.getUrl();
manager->get(QNetworkRequest(websiteurl));
}
Another way is to add extra parameters as an attribute in the QNetworkRequest.
// Save off the data in the request
QNetworkRequest req(websiteurl);
req.setAttribute(QNetworkRequest::User, QVariant::fromValue<MyClass>(objectdata));
req.setAttribute(QNetworkRequest::User + 1, QVariant::fromValue<MyClass2>(objectdata2));
manager->get(req);
...
// Retrieve the data from the reply
auto data1 = reply->request().attribute(QNetworkRequest::User).value<MyClass>();
auto data2 = reply->request().attribute(QNetworkRequest::User + 1).value<MyClass2>();