Storing data from QnetworkReply

[LeeH]

@mrjj

Hello

@SGaist said in Storing data from QnetworkReply:

You can use a QByteArray as a buffer to keep the data in memory. Just append new data to it as they arriving.

It was a suggestion that I was trying to make sense of in my example, so Im not sure tbh

[raven-worx]

@LeeH
are you calling your function upon the reply's finished signal?!

[LeeH]

@raven-worx

No because If I do that, I will be able to read the data from the other function in that ba object but it will not be stored, so if i try to call that same function outside of the class it will be empty.

[raven-worx]

@LeeH
but thats the point.
readAll() only returns the data when it tells you that it has finished.
Encapsulate your code into a helper class (each class has it's own QByteArray buffer).

[LeeH]

@raven-worx said in Storing data from QnetworkReply:

Encapsulate your code into a helper class (each class has it's own QByteArray buffer).

So would I have to set objects from other places directly to the reply data?

[mrjj]

@LeeH
Have a look at this sample
http://www.bogotobogo.com/Qt/Qt5_Downloading_Files_QNetworkAccessManager_QNetworkRequest.php
It uses a small helper class
class Downloader : public QObject
to manage the data it downloads. It responds to the finished signal.
Here it stores to file but you can as well store in ByteArray or whatever is needed.

Also its important to understand that you should NOT call the ReadData function yourself.
Your function will be called when data is ready. Its an asynchronous API.

[LeeH]

@mrjj

Ok thanks for that, I will check it out.

[LeeH]

@mrjj

Have a look at this sample
http://www.bogotobogo.com/Qt/Qt5_Downloading_Files_QNetworkAccessManager_QNetworkRequest.php
It uses a small helper class
class Downloader : public QObject
to manage the data it downloads. It responds to the finished signal.
Here it stores to file but you can as well store in ByteArray or whatever is needed.

I already have a class doing this job - as I said in the begining I can already save my reply data to file that can be read/used from anywhere in one signal slot connection, I just want to do the same thing without using a file so it can be read/used from anywhere in a single connection. If my class data object that has been assigned (or appended to) the value of reply's byte array is always empty when called, say from outside of the class (after download), meaning I have to re-download everytime I need the same data, then the reply data is not stored to my object is it?

[mrjj]

@LeeH said in Storing data from QnetworkReply:
Hi
If you keep the instance of class Downloader around,
there is no reason you cannot keep the data for later.
Say if you append to a QByteArray variable defined as
class member in Downloader

Can you please show the actual code how you use your helper class and how you later
try to access the data?

[LeeH]

@mrjj said in Storing data from QnetworkReply:

Can you please show the actual code how you use your helper class and how you later
try to access the data?

Certainly.

header:

class data : public QObject{

    Q_OBJECT

public:
    data();
    void download();
    QByteArray get();

public slots:

    void output(QNetworkReply* rep);

private:
    QNetworkAccessManager* _qnam;
    QByteArray _ba;

};

source:

data::data(){}

void data::download(){

    _qnam = new QNetworkAccessManager(this);
    _qnam->get(QNetworkRequest(QUrl("http://www.google.com")));
    QObject::connect(_qnam, SIGNAL(finished(QNetworkReply*)), this, SLOT(output(QNetworkReply*)));
}

void data::output(QNetworkReply* rep){

        if(!rep->error()){

           _ba.append(rep->readAll());

        }
        rep->deleteLater();
    }

QByteArray data::get(){
    qDebug() << _ba;
}

main:

 data obj;
 obj.download();
 obj.get();

[jsulm]

@LeeH said in Storing data from QnetworkReply:

QNetworkReply

You should connect your output() slot to http://doc.qt.io/qt-5/qiodevice.html#readyRead signal.

[LeeH]

@jsulm said in Storing data from QnetworkReply:

You should connect your output() slot to http://doc.qt.io/qt-5/qiodevice.html#readyRead signal.

Hi

Do you mean another connection, something like this:

void data::download(){

   _qnam->get(QNetworkRequest(QUrl("http://www.google.com")));
   QObject::connect(_qnam, SIGNAL(finished(QNetworkReply*)), this, SLOT(output(QNetworkReply*)));
   QObject::connect(QIODevice, SIGNAL(readyRead()), this, SLOT(output(QNetworkReply*)));

}

I know the QIODevice usage here is wrong, but just trying to get an idea

thanks

[jsulm]

@LeeH No need for two connections, the one for readyRead() is enough

[LeeH]

@jsulm

Ok... so how should I use QIOdevice here:

QObject::connect(QIODevice, SIGNAL(readyRead()), this, SLOT(output(QNetworkReply*)));

i get error: "expecting primary expression before ',' token" and it can't be instantiated

thanks

[m.sue]

Hi @LeeH

You need the QIODevice type object not the class name there.

-Michael.

[LeeH]

@m.sue

Hi,

QIODevice is an abstract class.

[m.sue]

Hi @LeeH

then the object of the derived class that you use.

-Michael.

[LeeH]

@m.sue said in Storing data from QnetworkReply:

then the object of the derived class that you use.

I modified my code to use readRead() from QNetworkReply object and it still doesn't work:

...
void data::download(){

_rep = _qnam->get(QNetworkRequest(QUrl("http://www.google.com")));
QObject::connect(_rep, SIGNAL(readyRead()), this, SLOT(output()));

}

void data::output(){

    if(!_rep->error()){

       _ba.append(_rep->readAll());

    }
    else{
        qDebug() << _rep->error();
    }
    _rep->deleteLater();
}

[m.sue]

Hi @LeeH

I would write: connect(_rep, SIGNAL(readyRead()), SLOT(output())); But this should not be essential.

So maybe output() is not a slot.

-Michael.

[mrjj]

@LeeH said in Storing data from QnetworkReply:

qDebug() << _rep->error();

Is line ever activated ?
is _ba.append called ?