Storing data from QnetworkReply

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 ?

LeeH

@m.sue said in Storing data from QnetworkReply:

So maybe output() is not a slot.

Hi it's always been a public slot... and i do get server reply data

LeeH

@mrjj said in Storing data from QnetworkReply:

Is line ever activated ?
is _ba.append called ?

Hi, there are no errors from server, and I always get reply.
I call _ba from main() using data::get()

mrjj

@LeeH
but is data appended?

if(!_rep->error()){
_ba.append(_rep->readAll());
qDebug() <<"size" << _ba.size();
}

have you tried with a breakpoint ?
is data::output() called?

LeeH

@mrjj

When I added:

qDebug() <<"size" << _ba.size();

i got:

size 2634

Yes data::output() is definately being called

mrjj

@LeeH
So what is not working ?
You clearly read data into _ba.

LeeH

@mrjj

but my data::get() I use to read _ba that i call from main() after downloading, is empty(""), where as if I read _ba from the slot inside the class I can see all my data

LeeH

@LeeH

You know I think It's best I just stick to saving to file, that seem's to be the only way I can be sure my data sticks around and can be used anywhere.... I thank everyone for their help, and apologize for wasting all of our time!

ambershark

@LeeH Well here's your problem:

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

You don't return anything. You should have gotten at least a compiler warning from that.

Anyway, just edit to be:

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

And your data.get() will work.

There is no reason to save the data to a file. You're just wasting resources on disk and slowing your app down for no reason.

jsulm

@LeeH said in Storing data from QnetworkReply:

Ok... so how should I use QIOdevice here

You use your QNetworkReply which is derived from QIODevice. And you cannot connect a class - you only can connect instances.
Did you read the documentation? http://doc.qt.io/qt-5/qnetworkaccessmanager.html
From there:

QNetworkRequest request;
request.setUrl(QUrl("http://qt-project.org"));
request.setRawHeader("User-Agent", "MyOwnBrowser 1.0");

QNetworkReply *reply = manager->get(request);
connect(reply, SIGNAL(readyRead()), this, SLOT(slotReadyRead())); // THIS ONE
connect(reply, SIGNAL(error(QNetworkReply::NetworkError)),
        this, SLOT(slotError(QNetworkReply::NetworkError)));
connect(reply, SIGNAL(sslErrors(QList<QSslError>)),
        this, SLOT(slotSslErrors(QList<QSslError>)));

mrjj

@LeeH said in Storing data from QnetworkReply:

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

Ahh, now i understand the confusion.
It won't stay in obj.download() until download is finished,
but return at once, as QNetwork classes are asynchronous

Then you call obj.get() but no data is there, because it was not downloaded yet.

So it do work, but not in the way you think it does :)

LeeH

@ambershark

Hi

@ambershark said in Storing data from QnetworkReply:

You don't return anything. You should have gotten at least a compiler warning from that.
Anyway, just edit to be:
QByteArray data::get(){
qDebug() << _ba;
return _ba;
}

Your right about returning _ba. I should have seen that as the function is not void... (my brains been fried working on real project lol), and I agree the compiler should have warned me about that. But that being said unfortunately has not resolved the problem. The output is still ""

However in the same function If I deliberately overwrite _ba, I get output:

QByteArray data::get(){
    _ba = "testing...";
    qDebug() << _ba;
    return _ba;
}

output: "testing..."

if I remove my call to data::get() in main() and output server data directly from the slot I get my data:

 if(!_rep->error()){
      qDebug() << _ba.append(_rep->readAll());
 }
 else{
        qDebug() << _rep->error();
 }
 _rep->deleteLater();

There is no reason to save the data to a file. You're just wasting resources on disk and slowing your app down for no reason.

Yep that was the reason for my post

mrjj

@LeeH
You did read why it dont work ?
obj.download();
obj.get();
Cannot work as download() is not a blocking call
so you will call obj.get(); BEFORE any data ever is read.

First when you get signal, its safe to use obj.get(); Not before.

J.Hilk

@LeeH according to what @mrjj said:

QObject::connect(_rep, SIGNAL(readyRead()), this, SLOT(output()));
QObject::connect(_rep, SIGNAL(finished()), this, SLOT(get()));

should do the trick.

get() will be called as soon as all data is written into the Bytearray.

LeeH

Hi
I had already modified my code in earlier post. You suggested QIODevice doc for readyRead() but I didn't realise QNetworkReply also had a readRead signal.

@jsulm said in Storing data from QnetworkReply:

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

LeeH

Hi guys

Ah at last it now works! When I did what @mrjj said:

Cannot work as download() is not a blocking call
so you will call obj.get(); BEFORE any data ever is read.

and then what @J.Hilk said after making data::get() a slot:

QObject::connect(_rep, SIGNAL(readyRead()), this, SLOT(output()));
QObject::connect(_rep, SIGNAL(finished()), this, SLOT(get()));

Success... Thanks so much to EVERYONE that helped!

Lee