QT - C++ - HTTP Request and Reply

Vildnex

I'm new to QT and I would like some help if could give it to me.

So I'm trying to create a class which will look something like this

class WeatherAPI : public QObject {
Q_OBJECT
public:
    explicit WeatherAPI(QObject *parent = nullptr);

public slots:
    void readData(QNetworkReply *reply);

private:
    QNetworkAccessManager *manager;
};

Where the constructor will be:

WeatherAPI::WeatherAPI(QObject *parent) : QObject(parent) {
    manager = new QNetworkAccessManager(this);
    QObject::connect(manager, SIGNAL(finished(QNetworkReply * )), this, SLOT(readData(QNetworkReply * )));
    QUrl url("http://dummy.restapiexample.com/api/v1/employees");
    manager->get(QNetworkRequest(url));
}

and the readData function will be:

void WeatherAPI::readData(QNetworkReply *reply) {
    if (reply->error() == QNetworkReply::NoError) {
        QStringList propertyNames;
        QStringList propertyKeys;

        QString strReply = (QString) reply->readAll();

        qDebug() << strReply;

        QJsonDocument jsonResponse = QJsonDocument::fromJson(strReply.toUtf8());

        QJsonObject jsonObject = jsonResponse.object();

        QString data = jsonObject["status"].toString();
        qDebug() << data;
    } else {
        qDebug() << "ERROR";
    }
    delete reply;
}

And the call of the WeatherAPI will be done into mainwindow.cpp like this.

MainWindow::MainWindow(QWidget *parent) : QMainWindow(parent), ui(new Ui::MainWindow) {
    ui->setupUi(this);

    WeatherAPI api(this);
}

Because I just care about that request to be done successfully for the moment at least.

Now the tricky part comes, when I'm going to run this program it will never enter into readData
function, I don't know why, so in other words, I'm NOT going to receive any reply.

But, if I will change the constructor to be like this:

WeatherAPI::WeatherAPI(QObject *parent) : QObject(parent) {
    QEventLoop eventLoop;
    QNetworkAccessManager manager;
    QObject::connect(&manager, SIGNAL(finished(QNetworkReply * )), &eventLoop, SLOT(quit()));
    QNetworkRequest req;
    QNetworkReply *reply;
    QString url = "http://dummy.restapiexample.com/api/v1/employees";
    req.setUrl(url);
    reply = manager.get(req);
    eventLoop.exec();
    QJsonDocument jsonPageDoc = QJsonDocument::fromJson(reply->readAll());
    QJsonObject jsonPageObj = jsonPageDoc.object();
    qDebug() << jsonPageObj["status"].toString();
}

Then everything is going to work properly, except that I can't do this because there is not going to be anything asynchrony, or in other words, everything is going to run on the main thread.
Could any of you guys tell me what's wrong with my first approach and why is not working? Why my code is never going to execute the readData function?

jsulm

@Vildnex said in QT - C++ - HTTP Request and Reply:

WeatherAPI api(this);

This is a local variable and will disappear as soon as constructor terminates.
Either make it class member or allocate on the heap.

dheerendra

WeatherAPI api(this);

This object no more exist once the contractor completes.