Read Data From URL

Ketan__Patel__0011

Hello Friends And Qt Experts

i am trying to read data from any particular URL

But between the process my application is hang or not responding

        qDebug() << "Pointer --> 1";
        QNetworkAccessManager  manager;
        qDebug() << "Pointer --> 2";
        QNetworkReply *response = manager.get(QNetworkRequest(QUrl(QString::fromStdString("MY_URL"))));
        qDebug() << "Pointer --> 3";
        QEventLoop event;
        qDebug() << "Pointer --> 4";
        QObject::connect(response, SIGNAL(finished()), &event, SLOT(quit()));
        qDebug() << "Pointer --> 5";
        event.exec(); 
        qDebug() << "Pointer --> 6";
        QString content = response->readAll();
        qDebug() << "Pointer --> 7";
        std::string readBuffer = content.toStdString();
        qDebug() << "Pointer --> 8";

When my pointer is reach At event.exec() that time my application is hang or not responding

i am not getting Next message after "Pointer --> 5"

please help to solve this problem

Thanks in Advance

JonB

@Ketan__Patel__0011
Why are you using any event.exec()? You are supposed to read from the response in the finished() slot, with no quitting. (Your response/reply/manager object should be scoped so it/they live until then.)

jsulm

@Ketan__Patel__0011 said in Read Data From URL:

When my pointer is reach At event.exec() that time my application is hang or not responding

Of course it does. exec() is a blocking call. Why do you use a local event loop?
Qt is an asynchronous framework, you should use it as such.
There are also networking examples showing how to do it properly.

Ketan__Patel__0011

@JonB

Thanks For The Reply

But when i remove the event.exec() and run the application then i didn't the response.

jsulm

@Ketan__Patel__0011 said in Read Data From URL:

and run the application then i didn't the response.

Because your QNetworkAccessManager manager; is a local variable...

JonB

@Ketan__Patel__0011
That's why I wrote

Your response/reply/manager object should be scoped so it/they live until then.

So as @jsulm is saying, you have to look at the scope/lifetime of the variables you are using.

Ketan__Patel__0011

@jsulm

So i Have to make this variable QNetworkAccessManager manager; as a class member.

jsulm

@Ketan__Patel__0011 Yes

Ketan__Patel__0011

@jsulm
I am remove this line event.exec(); from my code And make QNetworkAccessManager manager; variable as a class member
but still i didn't the the response.

jsulm

@Ketan__Patel__0011 Do you mean finished signal was not emitted?
You should add error handling to your code.
And you CAN'T read the response just after sending the request, do it in a slot connected to finished signal...

Ketan__Patel__0011

@jsulm

response->errorString() function give me this error message
Error Is : Unknown error

jsulm

@Ketan__Patel__0011 As I said: you can't read response just after sending request. This is not how asynchronous APIs work. Read response in a slot connected ti finished signal. This is also what @JonB already wrote.

Ketan__Patel__0011

@jsulm

Thanks For Reply

So Do you have any Suggestion or Any Sample Code Or Any Block Of Code For it

jsulm

@Ketan__Patel__0011 Did you read the documentation? https://doc.qt.io/qt-5/qnetworkaccessmanager.html

QNetworkAccessManager *manager = new QNetworkAccessManager(this);
connect(manager, &QNetworkAccessManager::finished,
        this, &MyClass::replyFinished);

manager->get(QNetworkRequest(QUrl("http://qt-project.org")));

In MyClass::replyFinished you read the response.

And there are many examples: https://doc.qt.io/qt-5/examples-network.html

Ketan__Patel__0011

@jsulm

Thanks for the reply

I am try all are the solution

And Create One Small QWidget Application Example For it and my problem is solved but..
i am create one library in Qt any put my same code in my Class library functions
that time i didn't get the response from my URL.

jsulm

@Ketan__Patel__0011 In what app do you use that library? Does that app have a running Qt event loop?

Ketan__Patel__0011

@jsulm

Actually i am create My Library in QT And i am export The Some Function From My Library and used in others application (DLLImport And DLLExport)

jsulm

@Ketan__Patel__0011 But does this application have a Qt event loop?

Ketan__Patel__0011

@jsulm
No that Application is not Qt Based But My Library Is Qt Based

jsulm

@Ketan__Patel__0011 said in Read Data From URL:

But My Library Is Qt Based

That is clear. But without Qt event loop Qt networking isn't going to work. You could execute networking part (from your DLL) in a thread with Qt event loop.